Quantum device and methods for imaging or measuring a physical property

Abstract

The invention refers to a quantum device (10) for imaging and / or measuring a physical property of a sample (12), wherein a controller (24) is configured to control the microwave source (20) to simultaneously generate a microwave radiation having a first frequency and a microwave radiation having a second frequency, the first frequency being in a first frequency range in which the first energy level resonates with the microwave radiation, and the second frequency being in the first frequency range or a second frequency range in which the second energy level resonates with the microwave radiation, and control the microwave source (20) to modulate – using one or more modulation frequencies - the amplitudes of the microwave radiation having the first frequency and the microwave radiation having the second frequency.

Description

[0001] Mewburn Reference: 008912990 Quantum Device and Methods for Imaging or Measuring a Physical Property

[0002] FIELD OF THE INVENTION

[0003] The invention relates to a quantum device for imaging and / or measuring a physical property, optionally a physical property of a sample. The quantum sensor device comprises a quantum sensor device and an excitation light source. The quantum sensor device includes colour centres in a sensor area. The quantum sensor device is configured to be arranged to be subjected to the physical property. The excitation light source is configured to generate excitation light directed to the quantum sensor device for exciting the colour centres to emit fluorescent light.

[0004] The invention further relates to a method for imaging and / or measuring a physical property, optionally a physical property of a sample, comprising the steps of (a) arranging a quantum sensor device including colour centres in a sensor area adjacent to the sample to be subjected to the physical property, the being configured to emit fluorescent light depending on the physical property, and (b) generating, by an excitation light source, excitation light directed to the quantum sensor device for exciting the colour centres to emit the fluorescent light.

[0005] Furthermore, the invention relates to a method for determining a quality of a sample.

[0006] The invention also refers to a controller for a quantum device for imaging and / or measuring a physical property, optionally a physical property of a sample, for example as used with the quantum device.

[0007] The invention relates to a computer-implemented method for imaging and / or measuring a physical property, a computer program, and a computer-readable storage medium.

[0008] BACKGROUND

[0009] Point defects in synthetic diamond material, particularly quantum spin defects and / or optically active defects, have been proposed for various use cases, such as in sensing, detecting, and quantum processing applications including: magnetometers; spin resonance devices such as nuclear magnetic resonance (NMR) and electron spin resonance (ESR) devices; spin resonance imaging devices for magnetic resonance imaging (MRI); and quantum information processing devices such as for quantum computing.

[0010] Many point defects have been studied in synthetic diamond material including: silicon containing defects such as silicon-vacancy defects (Si-V), silicon di-vacancy defects (Si-V2), silicon-vacancy-hydrogen defects (Si-V:H), silicon di-vacancy hydrogen defects (S-V2:H); nickel containing defect; chromium containing defects; and nitrogen containing defects such asMewburn Reference: 008912990 nitrogen-vacancy defects (N-V), di-nitrogen vacancy defects (N-V-N), and nitrogen-vacancy-hydrogen defects (N-V-H). These defects are typically found in a neutral charge state or in a negative charge state. These point defects extend over more than one crystal lattice point. The term point defect as used herein is intended to encompass such defects but not include larger cluster defects, such as those extending over ten or more lattice points, or extended defects such as dislocations which may extend over many lattice points.

[0011] The negatively charged nitrogen-vacancy (NV) defect in synthetic diamond material has attracted a lot of interest as a useful quantum spin defect because it has several desirable features including:

[0012] The electron spin states of the NV- centres can be coherently manipulated with high fidelity owing to a long coherence time (which may be quantified and compared using the transverse relaxation time or spin-spin relaxation time T2);

[0013] The electronic structure of the NV- centres allows the defect to be optically pumped into its electronic ground state allowing such defects to be placed into a specific electronic spin state even at non-cryogenic temperatures. This can negate the requirement for expensive and bulky cryogenic cooling apparatus for certain applications where miniaturization is desired.

[0014] Furthermore, the defect can function as a source of photons which all have the same spin state.

[0015] The electronic structure of the NV- centres comprises emissive and non-emissive electron spin states which allows the electron spin state of the defect to be read out through photons. This is convenient for reading out information from synthetic diamond material used in sensing applications such as magnetometry, spin resonance spectroscopy and imaging. Furthermore, it is a key ingredient towards using the NV- defects as qubits for long-distance quantum communications and scalable quantum computation. Such results make the NV- defect a competitive candidate for solid-state quantum information processing (QIP).

[0016] NV- centres are excellent magnetic field sensors and have been used for AC as well as DC magnetic field detection in various experiments. A significant parameter of each magnetometry setup is its sensitivity to external magnetic fields. A smaller sensitivity, in units T / ^Hz, is favourable, measuring the ability to detect a smaller magnetic field in a shorter amount of time

[0017] SUMMARY

[0018] An object of the invention is to provide improvements for a quantum device, a controller, and method for providing improved imaging and / or measuring of physical property, optionally a physical property of a sample.Mewburn Reference: 008912990 At its most general, the invention refers to optically exciting the colour centres and imaging and / or measuring a physical property using the light emitted by the colour centres. For imaging and / or measuring a physical property, optionally a physical property of a sample, the colour centres are subjected to microwave radiation which influences the fluorescence of the colour centres. The fluorescence response of the colour centres caused by the physical property to be measured and the microwave radiation is detected at or close to one or more energy transitions or energy levels of the colour centres. The microwave radiation includes two or more frequencies which simultaneously interact with the one or more energy transitions or energy levels. The two or more frequencies of the microwave radiation are amplitude-modulated such that the fluorescence response of the colour centres can be extracted for each of the two or more frequencies from the fluorescence response of the colour centres. For example, a change in the fluorescence response may be indicative of a change in the physical property.

[0019] According to a first aspect, there is provided a quantum device for imaging and / or measuring a physical property, optionally a physical property of and / or from a sample. The quantum sensor device comprises a quantum sensor device, an excitation light source, a microwave source, and magnetic source, and / or a controller. The quantum sensor device includes colour centres in a sensor area. The quantum sensor device is configured to be subjected to the physical property, optionally the quantum sensor device is configured to be arranged adjacent to the sample to be subjected to the physical property, such as an electromagnetic field. The colour centres are configured to emit fluorescent light depending on the physical property. The excitation light source is configured to generate excitation light directed to the quantum sensor device for exciting the colour centres to emit fluorescent light. The microwave source includes a microwave antenna for emitting microwave radiation towards the sensor area. The microwave source is configured to generate microwave radiation including at least two different frequencies (e.g. at least having a first frequency and a second frequency) and to modulate an amplitude of the generated microwave radiation. The magnetic source is provided for generating a device magnetic field in the sensor area. The device magnetic field induces a split of an energy level of the colour centres into at least a first energy level and a second energy level. The controller is in data-communication with the microwave source. The controller is configured to (i) control the microwave source to simultaneously generate a microwave radiation having a first frequency and a microwave radiation having a second frequency, the first frequency being in a first frequency range in which the first energy level resonates with the microwave radiation, and the second frequency being in the first frequency range or a second frequency range in which the second energy level resonate with the microwave radiation having the second frequency, and (ii) control the microwave source to modulate - using one or more modulation frequencies - the amplitudes of the microwave radiation having the first frequency and the microwave radiation having the second frequency.Mewburn Reference: 008912990 In some examples, the quantum sensor device further comprises an optical sensor and optics. Optionally, the optical sensor includes one or more pixels and is configured to generate electronic signals indicative of an intensity of the light emitted by the colour centres. The controller may be in data-communication with the optical sensor. Further optionally, the optics are regarded as optics and / or are configured to project the colour centres onto the optical sensor. In some embodiments, the controller may be further configured to (iii) record - for each pixel - the electronic signals received from the optical sensor for the modulated amplitudes of the microwave radiation having the first frequency and / or the microwave radiation having the second frequency, (iv) extract - for each pixel and using the one or more modulation frequencies - data corresponding to the first frequency and the second frequency from the electronic signals, and / or (v) calculate the physical property, optionally the physical property of the sample, using the extracted data corresponding to the first frequency and the second frequency.

[0020] According to a second aspect, there is provided a method for imaging and / or measuring an physical property, optionally a physical property from and / or of a sample, comprising the steps of (a) arranging a quantum sensor device including colour centres in a sensor area to be subjected to the physical property, optionally adjacent to the sample to be subjected to the physical property of the sample, the colour centres being configured to emit fluorescence light depending on the physical property, (b) generating, by an excitation light source, excitation light directed to the quantum sensor device for exciting the colour centres to emit the fluorescence light, (d) generating, by a magnetic source, a device magnetic field in the sensor area, the device magnetic field inducing a split of an energy level of the colour centres into at least a first energy level and a second energy level, (e) controlling a microwave source for simultaneously generating a microwave radiation having a first frequency and a microwave radiation having a second frequency, the first frequency being in a first frequency range in which the first energy level resonates with the microwave radiation, and the second frequency being in the first frequency range or a second frequency range in which the second energy level resonates with the microwave radiation, and (f) modulating - using one or more modulation frequencies - the amplitudes of the microwave radiation having the first frequency and the microwave radiation having the second frequency, recording - for each pixel of the optical sensor - the electronic signals received from the optical sensor for the modulated amplitudes of the microwave radiation having the first frequency and / or the microwave radiation having the second frequency.

[0021] In some examples, the method includes the steps of (c) projecting, by optics, the colour centres onto the optical sensor, (g) extracting - for each pixel and using the one or more modulation frequencies - data corresponding to the first frequency and the second frequency from the electronic signals, and / or (h) calculating the physical property, optionally the physical property ofMewburn Reference: 008912990 the sample, using the extracted data corresponding to the first frequency and the second frequency.

[0022] Steps (a) to (h) may be executed in alphabetical order. However, it is also possible that the ordering of one or more steps may be changed, two or more steps are simultaneously executed, one or more steps are omitted, and / or one or more steps are repeated twice or more for the method described herein.

[0023] According to a third aspect, there is provided a controller for a quantum device for imaging and / or measuring a physical property, optionally a physical property from and / or of a sample. The quantum device may be configured as described herein and / or comprises a quantum sensor device and / or a magnetic source. The quantum sensor device includes colour centres in a sensor area. The quantum sensor device is configured to be subjected to the physical property, optionally configured to be arranged adjacent to the sample to be subjected to the physical property. The colour centres are configured to emit fluorescent light depending on the physical property. The magnetic source is provided for generating a device magnetic field in the sensor area. The device magnetic field induces a split of an energy level of the colour centres into at least a first energy level and a second energy level. The controller comprises a first output port and a second output port. The first output port is configured to be connected to an excitation light source. The excitation light source is configured to generate excitation light directed to the quantum sensor device for exciting the colour centres to emit the fluorescent light. The second output port is configured to be connected to a microwave source including a microwave antenna for emitting microwave radiation towards the sensor area. The input port is configured to be connected to an optical sensor including one or more pixels. The optical sensor is configured to generate electronic signals indicative of an intensity of the light emitted by the colour centres. The controller is configured to (i) control the microwave source to simultaneously generate a microwave radiation having a first frequency and a microwave radiation having a second frequency, the first frequency being in a first frequency range in which the first energy level resonates with the microwave radiation, and the second frequency being in the first frequency range or a second frequency range in which the second energy level resonates with the microwave radiation, and (ii) control the microwave source to modulate - using one or more modulation frequencies - the amplitudes of the microwave radiation having the first frequency and the microwave radiation having the second frequency.

[0024] In some examples, the controller includes an input port configured to be connected to an optical sensor including one or more pixels, the optical sensor being configured to generate electronic signals indicative of an intensity of the light emitted by the colour centres. Optionally, the controller is further configured to (iii) record - for each pixel - the electronic signals received from the optical sensor for the modulated amplitudes of the microwave radiation having the firstMewburn Reference: 008912990 frequency and / or the microwave radiation having the second frequency, (iv) extract - for each pixel and using the one or more modulation frequencies - data corresponding to the first frequency and the second frequency from the electronic signals, and / or (v) calculate the physical property, optionally the physical property of the sample, using the extracted data corresponding to the first frequency and the second frequency.

[0025] According to a fourth aspect, there is provided a computer-implemented method for imaging and / or measuring a physical property, optionally a physical property from and / or of a sample. The quantum device may be configured as described herein and / or comprises a quantum sensor device and / or a magnetic source. The quantum sensor device includes colour centres in a sensor area. The quantum sensor device is configured to be subjected to the physical property and / or is configured to be arranged adjacent to the sample to be subjected to the physical property. The colour centres are configured to emit fluorescent light depending on the physical property. The magnetic source is provided for generating a device magnetic field in the sensor area. The device magnetic field induces a split of an energy level of the colour centres into at least a first energy level and a second energy level. The method comprises the steps of (A) generating control signals to be sent to an excitation light source such that the excitation light source generates excitation light directed to the quantum sensor device for exciting the colour centres to emit the fluorescent light, and / or (B) generating control signals to be sent to a microwave source for simultaneously generating microwave radiation having a first frequency and a microwave radiation having a second frequency, the first frequency being in a first frequency range in which the first energy level resonates with the microwave radiation, and the second frequency being in the first frequency range or a second frequency range in which the second energy level resonates with the microwave radiation.

[0026] In some examples, the method further includes the following steps: (C) receiving electronic signals indicative of an intensity of the light emitted by the colour centres from an optical sensor including a one or more pixels, (D) recording - for each pixel - the electronic signals received from the optical sensor for the modulated amplitudes of the microwave radiation having the first frequency and / or the microwave radiation having the second frequency, (E) extracting - for each pixel and using the one or more modulation frequencies - data corresponding to the first frequency and the second frequency from the electronic signals, and / or (F) calculating the physical property, optionally the physical property of the sample, using the extracted data corresponding to the first frequency and the second frequency.

[0027] Steps (A) to (F) may be executed in alphabetical order. However, it is also possible that the ordering of one or more steps may be changed, two or more steps are simultaneously executed, one or more steps are omitted, and / or one or more steps are repeated twice or more for the method described herein.Mewburn Reference: 008912990

[0028] According to a fifth aspect, there is provided a computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the steps of the method as described herein.

[0029] According to a sixth aspect, there is provided a computer-readable storage medium comprising instructions which, when executed by a computer, cause the computer to carry out the steps of the method as described herein.

[0030] According to a seventh aspect, there is provided a method for controlling a quality of a sample comprising the steps of (a) imaging and / or measuring a physical property of the sample using the method as described herein, optionally in real-time, and / or (b) determining the quality of the sample based on the imaged and / or measured physical property of the sample, optionally in real-time.

[0031] With known quantum devices and methods for imaging and / or measuring electromagnetic field, the frequency of the microwave radiation is sequentially varied / swept for determining changes in the fluorescence of the colour centres which can be indicative of the physical property of the sample and interacting with the colour centres. The sequential measurements of the fluorescence increase the time that is required for determining the physical property of the sample. The inventors have discovered that two or more frequencies can be simultaneously emitted by the microwaves source for imaging and / or measuring the physical property, e.g. the physical property of the sample. This can be done by modulating the amplitude of the microwave radiation having one or more frequencies.

[0032] The fluorescence response of the colour centres based on the excitation of the microwave radiation including two or more frequencies is a mixture of the fluorescence responses of the colour centres based on the first frequency, the second frequency, et cetera of the one or more frequencies simultaneously emitted by the microwave source. To extract the frequencydependent fluorescence response of the colour centres, the amplitude modulation can be used to extract the frequency dependent fluorescence response. For example, the fluorescence response of the colour centres corresponding to the first frequency exhibits the amplitude modulation of the first frequency. Similarly, the fluorescence response of the colour centres corresponding to the second frequency exhibits the amplitude modulation of the second frequency. In this way, the fluorescence response of the colour centres responding to the first frequency can be distinguished from the fluorescence response of the colour centres corresponding to the second frequency. In other words, the information imprinted by the amplitude modulation can be used to extract the fluorescence behaviour of the colour centres as excited by the microwave radiation having the first frequency and the microwave radiation having the second frequency.Mewburn Reference: 008912990

[0033] In this way, the measurement time can be reduced, for example by the number of frequencies that are simultaneously emitted by the microwave source. For example, if two frequencies are simultaneously emitted, the measurement time can be halved. If 10 frequencies are simultaneously emitted, the measurement time can be reduced to a tenth. It is immediately apparent that the solution provided by this invention can significantly reduce the overall time for imaging and / or measuring a physical property, e.g. the physical property of the sample. This may provide for real-time measurements of the physical property of the sample. For example, a typical measurement time of quantum devices of the prior art is approximately 1.5 hours. If 10 frequencies are simultaneously measured, this can be reduced to 9 minutes. Of course, if more frequencies are simultaneously generated, the measurement time can be reduced even further.

[0034] The quantum device can be provided for measuring a physical property that is present in the sample, altered by the sample, and / or generated by the sample. In some examples, the physical property is an electromagnetic field from and / or of the sample, such as an electromagnetic field that is present in the sample, altered by the sample, and / or generated by the sample. For example, the sample interacts with an external electromagnetic field and the quantum device is provided for measuring and / or analysing the interaction of the sample with the electromagnetic field. An example for this type of measurement are commonly known NMR measurements using the quantum device for measuring the NMR response.

[0035] Further, the physical property may additionally or alternatively include a temperature of the sample (e.g. temperature changes) and / or strain / stress within the sample which may change the interaction of the sample with an external electromagnetic field. Thus, the measured electromagnetic field may be used to determine the temperature of the sample, temperature changes in the sample, and / or stain / stress inside the sample. Temperature changes in the sample and / or stain / stress inside the sample may also generate an electromagnetic field that can be measured using the devices and methods described herein.

[0036] In some examples, the quantum device can be provided for directly measuring a temperature of the sample (e.g. temperature changes) and / or strain / stress within the sample. Changes in the temperature and / or strain / stress in the sample may result in changes in the temperature and / or strain / stress, respectively, in the quantum sensor device which in turn affect the fluorescence behaviour of the colour centres. For example, changes in the temperature may be transmitted to the quantum sensor device by thermal radiation, thermal convection, and / or thermal conduction.

[0037] In other examples, the quantum device can be provided for directly measuring a temperature (e.g. temperature changes) and / or strain / stress, such as the temperature and / or the strain / stress in the quantum sensor device. Changes in the temperature and / or strain / stress in the quantum sensor device may result in changes in the fluorescence behaviour of the colourMewburn Reference: 008912990 centres. The measurement of the temperature, strain / stress, and / or electromagnetic field may be simultaneously executed as the effect of the electromagnetic field on the colour centres may be independent from the effect of the temperature and / or strain / stress on the colour centres.

[0038] The electromagnetic field may refer to a magnetic field that is generated by and / or interacts with the sample. The electromagnetic field may also refer to microwave radiation that is reflected by the sample and / or that interacts with the sample (e.g. is absorbed by the sample and / or reflected by the sample). In some examples, the microwave radiation interacting with the sample may be generated by the microwave source.

[0039] The quantum device can also be provided for non-destructively probing the sample, for example the presence (or absence) of, e.g., metallic structures in optically non-transmissible material (such as deep metallization layers in a semiconductor circuitry). Thus, the quantum device may allow probing samples that cannot be analysed using optical imaging techniques. Further, nonionising radiation is used reducing the risk of the destruction of the sample as present with X-ray imaging techniques.

[0040] The colour centres may be provided only in the sensor area of the quantum sensor device. The quantum device is optionally configured to project the sensor area onto the optical sensor. The sensor area may cover the entire sample or a substantial portion thereof. In this way, sample probing is a fast process, for example compared to known scanning techniques, because the entire sample or substantial parts thereof can be measured in a single measurement. This may facilitate probing the sample in-line and / or a high throughput in fingerprinting samples.

[0041] Optionally, the speed of data generation (e.g. measuring the fluorescence response) as described herein can match the speed of the data analysis. Thus, a fast method for imaging and / or measuring a physical property is provided. Optionally, the invention allows widefield imaging of the sensor area.

[0042] The sample may include any material that interacts with electromagnetic radiation and / or is configured to generate electromagnetic radiation. The term “interacting” relates to changes in the intensity / amplitude (e.g. caused by reflection and / or absorption of the microwave radiation), changes in the polarisation, changes in the phase, and / or changes in the direction (e.g. refraction) of the electromagnetic radiation. In other words, the sample, e.g. the interaction of the sample with the incident electromagnetic radiation, changes a parameter of the incident electromagnetic radiation.

[0043] The microwave radiation may include two or more frequencies. This may mean that the microwave radiation that is emitted by the microwave source shows, when analysed with regard to its frequency spectrum, two or more frequencies. For example, a microwave electromagnetic wave having a first frequency and microwave electromagnetic wave having a second frequencyMewburn Reference: 008912990 are combined or multiplexed prior to being emitted by the microwave antenna. The emitted microwave radiation includes the first frequency and the second frequency. Commonly known techniques for generating microwave radiation having two or more frequencies can be used.

[0044] Such an emitted microwave radiation may interact with the colour centres as a microwave radiation having a first frequency and as a microwave radiation having a second frequency. Consequently, the terms microwave radiation including a first frequency and a second frequency may be interchangeable used as microwave energy having the first frequency and microwave energy having a second frequency.

[0045] The controller generates control signals that can be sent to the microwave source which generates the microwave radiation having the two or more frequencies as set by the controller.

[0046] The microwave source may include a microwave generator for generating the microwave radiation having a first frequency and the second frequency (optionally, a third, fourth, fifth, sixth, et cetera frequencies). The microwave generator may be configured to generate the microwave radiation having constant first, second, etc. frequencies during a single measurement.

[0047] The microwave source may include a first microwave generator generating the microwave radiation having the first frequency, a second microwave generator generating the microwave radiation having the second frequency, etc. The microwave source may further include a multiplexer which is coupled between the microwave antenna and the first, second, etc. microwave generators for multiplexing the first, second, etc frequencies for being emitted by the microwave antenna.

[0048] The microwave source may further include an amplitude modulator which is configured to modulate the amplitude of the microwave radiation generated by the microwave generator. Commonly used amplitude modulators can be used. The amplitude modulator may be configured to modulate the microwave radiation having the first frequency with a first modulation frequency and to modulate the microwave radiation having the second frequency with a second modulation frequency. The amplitude modulator may be configured to vary the amplitude of the microwave radiation during a measurement. Optionally, each of the first, second, etc microwave generators is associated with a respective amplitude modulator. The amplitude modulated frequencies can be then multiplexed by the multiplexer.

[0049] A measurement may refer to recording of the electronic signals for a specific first and / or second frequency of the microwave radiation and / or a specific configuration of the device magnetic field over a time period over which the microwave radiation of the first and / or second frequencies isMewburn Reference: 008912990 modulated. This means that, for a measurement and for each pixel, a plurality of electronic signals is recorded, namely for each modulation of the amplitude of the microwave radiation of the first and / or second frequencies and / or over a predetermined time period of the modulation of the microwave radiation of the first and / or second frequencies. In some examples, the plurality of electronic signals is recorded one after the other (in the time domain). This is done because the data can only be extracted from electronic signal of a single recording (i.e. with a given frequency and a given amplitude modulation).

[0050] For example, the electronic signals are recorded for the microwave radiation having the first and / or the second frequencies and for a first amplitude of the microwave radiation having the first and / or second frequencies. This measurement is repeated for the microwave radiation having the first and / or the second frequencies and for a second amplitude of the microwave radiation having the first and / or second frequencies. The first and second amplitudes are modulated amplitudes of the microwave radiation. For example, the first and second amplitudes are steps or values of the modulated amplitude.

[0051] In an optional embodiment, the controller is configured to control the microwave source to modulate the microwave radiation such that the amplitudes of the microwave radiation having the first frequency and the microwave radiation having the second frequency remains constant during the recording of the electronic signals and are changed between recording of the electronic signals.

[0052] In this way, the recording of the electronic signals reflects the fluorescence response of the colour centres for a given frequency and amplitude of the microwave radiation. This may increase the sensitivity and / or contrast of the measurement.

[0053] During the recording of the electronic signals, the amplitude of the microwave radiation having a first and / or the second frequency is not changed and remains at the current amplitude from the plurality of amplitudes that are generated during the amplitude modulation. For example, the amplitude of the microwave radiation having the first and / or second frequencies is stepwise changed by the amplitude modulation. For example, the amplitude is incrementally increased from zero amplitude or incrementally decreased from a maximal amplitude. For example, the amplitude is increased by 0.1 %, 0.5 %, 1 %, 5%, 10 %, 20 %, 25 % or 50 % of the maximum amplitude in each step of the amplitude modulation. It is also possible that the step size is varied between steps, i.e. to provide a non-uniform change in the amplitude within a measurement.

[0054] For example, the electronic signals are recorded for a predetermined period of time during which the microwave radiation is held at the first and / or second frequencies and has a constantMewburn Reference: 008912990 amplitude. This predetermined period of time or recording the electronic signals may correspond to a frame of the optical sensor, e.g. the time period during which the optical sensor is subjected to the fluorescent light emitted by the colour centres and / or generates the electronic signals. For example, predetermined period of time or recording the electronic signals may correspond to a frame of a camera (if the imaging sensor is part of a camera, e.g. CCD-camera).

[0055] The microwave radiation may also be generated before the electronic signals are recorded. For example, the recording of electronic signal is a readout phase before or during which the colour centres are excited by the excitation light and simultaneously manipulated using the microwave radiation. In some examples, the colour centres are excited by the excitation light source, manipulated by the microwave radiation, again excited by the excitation light, and as a last step, the fluorescence response of the colour centres is read out using the optical sensor (i.e. the electronic signals are generated). During all these steps, the frequencies and / or the amplitudes of the microwave radiation can be held constant. Once this step sequence is complete, the amplitude and / or the frequency may be changed and the same step sequence is repeated.

[0056] Alternatively, the amplitude of the microwave radiation can be continuously (non-stepwise) changed and / or may not be constant during the recording of the electronic signals (and / or during the above-described steps prior to the read-out phase). In this case, the amplitude of the microwave radiation is varied during the recording of the electronic signals and / or during the above-described steps prior to the read-out phase). Depending on the rate of change in the amplitude modulation and / or the time period for recording electronic signals (and / or during the above-described steps prior to the read-out phase), the change in the amplitude may be less than 0.1 %, 0.5 %, 1 %, 5%, 10 %, or 20 % of the maximum amplitude. In this case, the change in the amplitude during the recording of electronic signals (and / or during the above-described steps prior to the read-out phase) may not significantly affect and / or change the electronic signals (compared to the effect of the electromagnetic field to be detected) such that the electromagnetic field can still be detected with a high contrast and / or sensitivity.

[0057] The temporal behaviour of the amplitude modulation may be periodic and / or the amplitude modulation has a sinusoidal, cosinusoidal, triangular, or squared shape or other types of waveforms.

[0058] A measurement may refer to the multiple recordings of the electronic signals (frames) wherein each recording of the electronic signal refers to a different amplitude (in case the amplitude is held constant during the recording of the electronic signals) or (small) amplitude range (in case the amplitude is varied during the recording of electronic signals) of the amplitude modulation. For example, one or more periods of the amplitude modulation may be recorded for oneMewburn Reference: 008912990 measurement. For example, a measurement includes 10, 20, 50, 75, 100, 125, 150, 200, 300, or 500 recording of the electronic signals.

[0059] Including two or more periods of the amplitude modulation for a measurement can increase the sensitivity and / or the contrast of the determination of the electromagnetic field. However, it increases the time of measurement because more recordings of the electronic signals need to be conducted for a single measurement.

[0060] The recording of the electronic signals and / or the above-described steps prior to the recording of the electronic signals may require between 0.1 ps to 1000 ms, optionally between 1 ps to 500 ms, further optionally between 10 ps to 250 ms. The recordings for an amplitude modulation for the same first and second frequency (e.g. the repetition of a single recording for each varied amplitude of the amplitude modulation with unchanged first and second frequencies) may require between 1 s to 100,000 s, optionally between 10 s to 50,000 s.

[0061] The frequency of the amplitude modulation may be between 1 Hz and 500 kHz, optionally between 2 Hz and 1 kHz, further optionally between 10 Hz and 100 Hz. The number of frequency changes (which may correspond to the frequency step of the frequency sweep) may between 10 and 1000, optionally between 25 to 500, further optionally between 50 to 150. A measurement may last between 1 s to 100,00 s, optionally between 10 s and 10,000s.

[0062] Each measurement may be repeated for a varied first frequency and / or a varied second frequency to measure the electromagnetic field at various frequencies. This can increase the sensitivity and / or contrast of the determination of the electromagnetic field.

[0063] The electronic signals for each measurement may exhibit a temporal change which is induced by the amplitude modulation. The electronic signals for each measurement may cover sequential time periods over which the optical sensor is read out and / or the fluorescence response of the colour centres is recorded. The electronic signals for each of these time periods may be combined to generate a sequence of electronic signals that follow the temporal change ofthe amplitude of the microwave radiation.

[0064] The above considerations relate to the interaction ofthe microwave radiation with colour centres which may include that all colour centres react in the same way to the microwave radiation emitted by the microwave source. However, the emitted microwave radiation may interact with a sample resulting in a local variation ofthe microwave radiation at the position ofthe colour centres such that different colour centres experience different microwave radiations and, therefore, exhibit different fluorescence responses. Furthermore, the electromagnetic field ofthe sample may also locally vary the fluorescence response ofthe colour centres with regard to theMewburn Reference: 008912990 emitted microwave radiation. One or both aspects can be used to measure and / or image the electromagnetic field from the sample.

[0065] The term “fluorescence response” may refer to the fluorescent light emitted by the colour centres as a result of the optical excitation of the excitation light and the interaction of the colour centres with the physical property of the sample, e.g. the electromagnetic field from the sample, and / or the microwave radiation generated by the microwave source. The fluorescence response may refer to the intensity of the fluorescent light emitted by the colour centres. For example, the electromagnetic field from the sample and / or the microwave radiation generated by the microwave source may populate or depopulate certain energy levels (e.g. depending on the frequency or energy of the microwave radiation and / or the electromagnetic field from the sample) which can result in a change in the intensity of the fluorescent light emitted by the colour centres.

[0066] After impinging on the sample, at least one parameter of the microwave radiation (e.g. the amplitude, the phase, the frequency, the direction, polarity, etc) can be changed due to the interaction with the sample. For example, the microwave radiation impinges on an interface between a metallic layer and the electric material within the sample. At this interface, the microwave radiation is reflected which is an example of the interaction of the microwave radiation with the sample. This change in one or more parameters of the microwave radiation that is introduced by the sample may result in a changed electromagnetic field from the sample that is sensed by the quantum sensor device. This change in the sensed electromagnetic field may be recorded and analysed as described herein for imaging and / or measuring the sample. In other words, the microwave radiation interacting with the colour centres is varied or changed in two ways in this example: Firstly the microwave radiation is actively changed by varying the generation of microwave radiation and secondly the microwave radiation is passively changed by the sample which can be indicative of the configuration of the sample.

[0067] The sample may include one or more materials which each may have different properties of interaction with the external electromagnetic radiation, for example an absorption coefficient, a reflection coefficient, and / or a dielectric constant. For example, the sample interacts with the external electromagnetic radiation that at least one parameter of the external electromagnetic radiation is changed by more than 10%, more than 20%, more than 30%, more than 40%, more than 50%, more than 60%, more than 70%, more than 80%, or more than 90% and / or maximally by 100% (e.g. total reflection or absorption).

[0068] The interaction of the sample with the external electromagnetic radiation may be sufficiently substantial such that changes in the external electromagnetic radiation due to the interaction with the sample have a sufficiently significant effect on the fluorescent light emitted by the colour centre, e.g. the intensity of the fluorescent light emitted by the colour centres. StatedMewburn Reference: 008912990 differently, the interaction of the external electromagnetic radiation with the sample is sufficiently high such that it can be recorded using the colour centres with a sufficient signal-to-noise ratio. Of course, this strongly depends on the external electromagnetic radiation, the material properties of the sample, and / or the colour centres used. Examples of the external electromagnetic radiation interacting with the sample are the microwave radiation generated by the microwave source and / or the device magnetic field. A change in interaction with the external electromagnetic radiation may be due to changes in the sample, for example a different sample is placed in front of the quantum sensor device and / or properties of the sample change.

[0069] The quantum device may further include a sample holder for supporting and / or holding the sample, e.g. close to the quantum sensor device and / or the sensor area. The sample holder may be any device that is configured to removably support the sample and / or to which the sample can be removably attached, e.g. using fastening means. Commonly known sample holders may be used. The sample holder defines a sample area in which the sample is located when the sample is probed. The sample area may have a circular, quadratic or rectangular cross-section. The size of the sample area can include a maximal length / diameter of 100 pm, 200 pm, 300 pm, 400 pm, 500 pm, 600 pm, 700 pm, 800 pm, 900 pm, 1 mm, 2 mm, 2.54 mm (1”), 3 mm, 4 mm, 5 mm, 5.08 mm (2”), 7.62 mm (3”), 10 mm, 10.16or 2.54 mm (1”), 12.17 mm (5”), and / or a minimal length / diameter of 10pm. The size of the sample area may be, for example, 1000 pm2, 2000 pm2, 3000 pm2, 4000 pm2, 5000 pm2, 6000 pm2, 7000 pm2, 8000 pm2, 9000 pm2, 10000 pm2, 1 mm2, 2 mm2, 4 mm2, 10 mm2, 16 mm2, 50 mm2, 100 mm2, 150 mm2, or 200 mm2.

[0070] The sample holder can be configured to support the sample in such a position that the sample is close to or in contact with the sensor area of the quantum sensor device. In this way, the colour centres of the quantum sensor device can be arranged close to or directly adjacent to the sample. Optionally, the sample holder is configured to support the sample as close as possible to or in contact with the sensor area.

[0071] The quantum sensor device may be attached to the sample holder. For example, the sample is placed on the quantum sensor device that is in turn supported by the sample holder. It is also possible that the sample and the quantum sensor device are a single or unitary component. In this case, the sample may be regarded a portion of the quantum sensor device, e.g. a temperature sensing portion of the quantum sensor device. This may be implemented if the quantum device is used for measuring stress / strain and / or temperature.

[0072] In any case, for the measurement, the sample (whose physical properties are to be measured) is close to the colour sensors such that the colour sensors are affected by the physical properties of the sample.Mewburn Reference: 008912990 The quantum sensor device is optically transparent such that the excitation light can reach the colour centres without or only minimal loss of intensity. The quantum sensor device may include a sample side and an optics side which opposes the sample side. The quantum sensor device and the sample holder are configured to be arranged such that the sample is in contact with or directly adjacent to the sample side of the quantum sensor device.

[0073] The light generated by the excitation light may impinge on the optics side and travel through the quantum sensor device to reach the sensor area. The fluorescent light emitted by colour centres may exit the quantum sensor device at the optics side. It is also possible that the excitation light enters the quantum sensor device at the sample side and the fluorescent light exits the quantum sensor device at the optics side. The optics side may face the optics and / or the sample side may face the sample.

[0074] The quantum sensor device may have a cuboid or cylinder shape. For example, the quantum sensor device may have the shape of a plate or disc. In this case, the sample side and / or the optics side may form a flat, non-curved, and / or parallel surfaces. Alternatively, the quantum sensor device may form a lens wherein optionally the sample side is a flat surface and the optics side is curved and / or shaped to optically refract the impinging and / or exiting light.

[0075] The sensor area and / or the quantum sensor device may have maximal length / diameter of 100 pm, 200 pm, 300 pm, 400 pm, 500 pm, 600 pm, 700 pm, 800 pm, 900 pm, 1 mm, 2 mm, 2.54 mm (1”), 3 mm, 4 mm, 5 mm, 5.08 mm (2”), 7.62 mm (3”), 10 mm, 10.16or 2.54 mm (1”), 12.17 mm (5”), and / or a minimal length / diameter of 10pm. The size of the sample area may be, for example, 1000 pm2, 2000 pm2, 3000 pm2, 4000 pm2, 5000 pm2, 6000 pm2, 7000 pm2, 8000 pm2, 9000 pm2, 10000 pm21 mm2, 2 mm2, 4 mm2, 10 mm2, 16 mm2, 50 mm2, 100 mm2, 150 mm2, or 200 mm2.

[0076] The colour centres correspond to those elements within the quantum sensor device which can be energetically excited by the excitation light for emitting fluorescent light. The colour centres may be solid state quantum sensors which may be defects in the crystalline material of the quantum sensor device. The colour centres may be provided in the crystallin material by doping the material and / or treating the material (e.g. using a laser). Further, the quantum sensor device may be grown by epitaxy. This process can be controlled in such a way that the colour centres are provided in the desired concentration and / or location.

[0077] The quantum sensors may be arranged in a predefined volume or layer within the quantum sensor device. For example, the quantum sensors are arranged in a layer at or close to the sample side of the quantum sensor device. The layer in which the colour centres are arranged form the sensor area. It is possible that the colour centres are arranged in patterns.Mewburn Reference: 008912990 The sensor area may extend along the entire sample side or may extend over a section of the sample side. The sensor area may cover an area of between 0.01 mm2and 20 mm2, optionally 0.2 mm2to 2mm2, further optionally between 0.5 mm2to 1 mm2. The sensor area may have a thickness between 0.01 pm to 1 nm, optionally between 0.1 pm to 100 pm, further optionally between 1 pm and 50 pm. The thickness and / or the size of the sensor area may depend on the size and / or shape of the quantum sensor device and / or the optics.

[0078] Optionally, the sensor area may have a longitudinal extension and / or a thickness such that the entire sensor area can be projected onto the optical sensor. For example, the thickness of the sensor area is sufficiently small such that a sharp image of the colour centres can be projected onto the optical sensor. A sensor area having a large thickness would result in a blurred image of the colour centres on the optical sensor. Further, if the sample area has a large thickness, the distance between an individual colour centre and the sample would substantially vary which may introduce undesired differences in the interaction of the interacting microwave radiation with the colour centres.

[0079] The quantum sensor device may be a diamond with negatively charged nitrogen vacancy (NV ) centres as colour centres. Alternatively, the quantum sensor device may be made from silicon carbide (SiC) and the colour centres correspond to bandgap point defects. Further examples for the colour centres are point defects in hexagonal boron nitride.

[0080] The quantum sensor device may be permanently or removably attached to the sample holder. Thus, upon attaching a sample to the sample holder, the sample holder may support both the quantum sensor device and the sample. For example, the sample holder is configured such that the sample can be put or lie on the sample side of the quantum sensor device.

[0081] The excitation light source may comprise one or more lasers, one or more LEDs (Light Emitting Diodes) and / or one or more light sources with a broadband emission spectrum. The light source may generate light of a wavelength or narrow wavelength range (for example 10 nm, 20 nm, 50 nm or 100 nm). Optionally the wavelength or wavelength range generated by the excitation light source includes one or more wavelengths absorbed by the colour centres (e.g. that excite the colour centres such as the first and second energy levels). The excitation light source may also include a broadband light source which generates light having wavelengths over a wavelength range, for example a white light source. The wavelength(s) generated by the excitation light source may be chosen and / or selected such that the excitation light is absorbed by colour centres for exciting the colour centres. In other words, the energy of the light generated by the excitation light source may correspond to the energy required for exciting colour centres, for example for increasing the energy state of an electron of the colour centres.Mewburn Reference: 008912990 The excitation light source may be configured to continuously emit the excitation light during the entire measurement. This is often called continuous wave (CW) measurement. Alternatively, the excitation light source may be configured to emit pulses of the excitation light. For example, the excitation light source emits a first pulse of the excitation light prior to the emission of the microwave radiation and a second pulse of the excitation light after the emission or during the emission of the microwave radiation. The optical sensor can be triggered in such a way that it only records the fluorescent light during the emission of the second excitation light pulse and / or after the emission of the second excitation light pulse. The wavelength of the excitation light may be 532 nm.

[0082] For generating pulses, the excitation light source may include a modulator (such as an acoustooptic modulator (AOM)) and a light source that generates non-pulsed or cw light, e.g. one or more lasers, one or more LEDs (Light Emitting Diodes) and / or one or more light sources with a broadband emission spectrum. The modulator may be configured to modulate the light emitted by the light source. For example, the modulator may be configured to vary the amplitude and / or phase of the light emitted by the light source. Further, the modulator may be configured to control when and / or how long light can reach the colour centres. Thus, the modulator may be configured to generate pulsed light. The controller may be in data-communication with the modulator for controlling the excitation light, e.g. the duration and / or start time of the one or more laser pulses.

[0083] The excited colour centres emit fluorescent light because the energy state eventually returns to a lower energy state after being excited by the excitation light (an example is described in the background section above). The microwave radiation having a frequency in the first frequency range and / or a frequency in the second frequency range may resonate with transitions from or to the first and second energy levels, respectively. Thus, the microwave radiation in the first frequency range and / or the second frequency range may have an energy (as defined by frequency) that is equal to or similar to an energy gap corresponding to the transition from or to the first and second energy levels, respectively.

[0084] The first frequency range may be selected and / or set such that there is at least one frequency having an energy which corresponds to the first energy level. The second frequency range may be selected and / or set such that there is at least one frequency having an energy which corresponds to the second energy level. In other words, the first frequency range may include the first energy level. However, the first frequency range is not limited to the first energy level. Similar considerations apply for the second frequency range.

[0085] The first frequency and / or the second frequency may not be in resonance with the first energy level and / or the second energy level. For example, the first frequency and / or the second frequency are slightly off-resonance or significantly off-resonance with the first energy levelMewburn Reference: 008912990 and / or the second energy level. For example, the first frequency and / or the second frequency refer to a baseline of the first energy level and / or the second energy level. In other examples, the first frequency and the second frequency are on either side of the first or second energy level. A plurality of varied first frequencies and / or varied second frequencies may be measured, wherein at least one of the plurality of varied first frequencies and / or varied second frequencies is in resonance or close to resonance, i.e. corresponds to or is similar to, the first energy level and / or the second energy level.

[0086] The excitation of the colour centres can be induced by phonons. The energy gaps can be the same for both energy levels. Usually, the energy gap between the excited state and the lower energy state is lower than the energy of the excitation light such that the fluorescent light has a higher wavelength compared to the wavelength of the excitation light. For example, the excitation light of the NV- centres may be green and the fluorescent light may be red.

[0087] The excitation light source, the optical sensor, and the optics may form a wide-field microscope for exciting and / or imaging the colour centres. The beam path of the wide-field microscope may not have an aperture (also known as a pinhole), which is used to select a layer along the z-axis or optical axis of the optical path, as is common in confocal microscopy. In this way, the setup of the present invention can be simplified and / or the light yield increased.

[0088] The colour centres (which may be considered to be colour sensors or quantum sensors) may be exclusively located in the sensor area and the remainder of the quantum sensor device may be essentially free of colour centres. This enables the use of wide-field microscopy because there is no superposition of signals from the sensor area with signals from the remainder of the quantum sensor. The arrangement of the colour centres in a layer (and the thickness thereof) can be controlled during the manufacturing process of the quantum sensor device.

[0089] The magnification of the wide-field microscope could be 1x, 10x, 20x, 50x, 100x, 200x or400x. The magnification can be adjusted, for example, by the magnification of the optics. The imaging can be adjusted by varying the parameters magnification, number of pixels, and size of the optical sensor.

[0090] The optical sensor may be a device for recording two-dimensional images from light by electric or electronic means. Semiconductor-based optical sensors that can record light up to the midinfrared range can be used. Examples of optical sensors in the visible and near infrared range are CCD sensors or CMOS (Complementary metal-oxide-semiconductor) sensors which may have fast readout times, e.g. faster compared to CCD sensors. The optical sensor can convert an incident light into electrical or electronic signals, with the electrical and electronic signals indicating the intensity of the incident light and / or the wavelength of the incident light, optionally with spatial resolution. For example, the optical sensor has a plurality of pixels, each of whichMewburn Reference: 008912990 generates electrical or electronic signals. The electrical and electronic signals indicate the intensity of the incident light and / or the wavelength of the incident light. The plurality of electrical and electronic signals generated by the pixels could be converted into a two-dimensional image. However, as outlined in the following, the electronic signals are processed before an image is generated as outlined in the following.

[0091] The image sensor may have a number of pixels of 50x50 pixels; 250x250 pixels; 1000x1000 pixels; 2000x2000 pixels, 4000x4000 pixels or 8192x8192 pixels. The image sensor may be non-square and have one of the above values for the number of pixels along one direction. The size of the image sensor is optionally 1x1 pm2, 2.5x2.5 pm2, 5x5 pm2, 10x10 pm2, 25x25 pm2or 50x50 pm2. As mentioned, the image sensor can also be non-square and then have an edge length with the values mentioned.

[0092] It is also possible that the optical sensor includes a single pixel, for example a single optical detector such as a photodiode or avalanche photodiode (APD). Such a configuration of the optical sensor may be helpful for providing highly sensitive measurements of the emitted fluorescent light.

[0093] The optics may refer to an assembly of optical components and / or include one or more optical elements that are configured to provide optical paths for the excitation light and / or the fluorescent light emitted by the colour centres. For example, the one or more optical elements include an objective, lenses, a beam splitter, an optical filter, a mirror, and / or a dichroic mirror.

[0094] An optical path for exciting the colour centres may start from the excitation light source over a dichroic mirror, through an objective to the colour centres. An optical path for the fluorescent light may start from the colour centres through the objective and the dichroic mirror onto the optical sensor. Thus, there might be a common optical path through the objective. The dichroic mirror may be used to couple in the excitation light in the common optical path or couple out the fluorescent light from the common optical path. Those optical setups are known in the prior art.

[0095] The optics is configured to project the colour centres onto the optical sensor. The fluorescent light emitted by a group of colour centres may be projected onto a single pixel. In other words, the electronic signals generated by each pixel of the optical sensor may correspond to the intensity and / or wavelength of a corresponding group of colour centres. Stated differently, the optics projects a sub-volume of the sensor area onto a respective pixel. The fluorescent light emitted by the colour centres in this sub-volume is recorded by the respective pixel.

[0096] The microwave source may include a generator for generating microwave electromagnetic energy and a microwave antenna that is electrically coupled to the generator. The microwave antenna is configured to emit the microwave electromagnetic energy that is generated by theMewburn Reference: 008912990 generator. Thus, the microwave radiation is emitted at the microwave antenna. The microwave radiation may have a wavelength between 1 mm to 1 m or a frequency of between 300 GHz -300 MHz. The microwave source may be also configured to generate radiofrequency (RF) radiation which is usually considered to fall within a portion of the electromagnetic spectrum with frequencies ranging from 3 kHz to 300 GHz.

[0097] The generator of the microwave source may be configured to generate the microwave electromagnetic energy in wavelength ranges having respective energy ranges that correspond to first and second energy levels of the colour centres. In other words, the energy of the microwave radiation may be set to such an energy (as defined by the frequency) of the microwave radiation corresponds to an energy gap of the colour centres. Thus, the microwave radiation can be used to excite the colour centres and / or depopulate excited energy states of the colour centres. For example, the microwave radiation may be used to initiate a population transfer from an energy level to another energy level of the colour centres.

[0098] The microwave antenna may be a monopolar antenna or dipole antenna. The microwave antenna may include a ring structure, have the shape of a loop, and / or include one or more elongated structures (e.g. a rod) for emitting the microwave radiation. For example, the microwave antenna at least partially extends around the quantum sensor device. The microwave antenna may be shaped and / or located such that the electric field generated by the microwave radiation is approximately homogeneous over the sensor area and / or the sample area.

[0099] In some examples, the microwave radiation is used to manipulate the colour centres in such a way that it affects the fluorescence response of the colour centres upon excitation by the excitation light source. For example, the microwave radiation is provided for increasing the intensity of the fluorescent light emitted by the colour centres. This may be done by exciting the colour centres to an energy level at which the colour centres can absorb the excitation light.

[0100] Alternatively, the microwave radiation is provided for decreasing the intensity of the fluorescent light emitted by the colour centres. This may be done by depopulating energy states that are excited by the excitation light. Thus, the microwave radiation that is emitted by the microwave antenna and directly interacting with the colour centres influences the intensity of the fluorescent light emitted by the colour centres. For example, the microwave radiation may have a frequency (e.g. the first and / or the second frequency) that is in resonance with the colour centres or is off resonance in the first frequency range and the second frequency range. Thus, the application of the microwave radiation (directly from the antenna) varies the fluorescence response of the colour centres.Mewburn Reference: 008912990 The presence of the sample and / or an external electromagnetic field changes the variation of the fluorescence response of the colour centres as induced by the microwave radiation. Thus, the quantum device is based on determining deviations in the fluorescence response (around a resonance with the microwave radiation) which is caused by the sample and / or an external electromagnetic field.

[0101] The quantum device may include a magnetic source which optionally includes a permanent magnet and / or one or more coils that are configured to generate the device magnetic field. The magnetic source may also be configured to vary a configuration of the device magnetic field. The configuration of the device magnetic field may refer to the orientation and / or strength of the device magnetic field. The device magnetic field of a first configuration may differ in the orientation and / or strength from the device magnetic field of a second configuration. For example, the device magnetic field of the first configuration may have the same orientation as the device magnetic field of the second configuration and differs in the strength of the respective device magnetic field. The configuration of the device magnetic field (e.g. the strength of the device magnetic field) may be tuned such that the gradient of change in the electronic signals (e.g. a change in the absorption and / or emission of the light by the colour centres) is maximal.

[0102] The device magnetic field generated by the magnetic source may be constant for the time over which the electronic signals, the microwave radiation, and / or the excitation light are generated. In other words, the device magnetic field generated by the magnetic source may be constant for the time of one measurement. The device magnetic field generated by the magnetic source is at least present in the sample area and / or the sensor area. Due to the proximity of the sample area and the sensor area, the device magnetic field generated by the magnetic source may also be present in both the sensor area and the sample area. The device magnetic field generated by the magnetic source may be configured to be constant and / or homogeneous throughout the sample area and / or the sensor area.

[0103] The magnetic source may be provided for inducing a split of an energy level, such as a Zeeman split as described in the background section above which ultimately results in the Hyperfine states that are measured in some embodiments. In the absence of the device magnetic field, the colour centres include at least one energy level which is involved in the generation of the fluorescent light. For example, this energy level may correspond to the excited state or the ground state of the colour centres. The device magnetic field splits this energy level into two energy levels that are separated by a predefined energy gap. For example, the energy gap may be proportional to the strength of the device magnetic field.

[0104] The first energy level and the second energy level are also involved in the generation of the fluorescent light. Thus, a graph or curve of the detected fluorescent light shows two extrema (e.g. a peak or dip) of the intensity of the fluorescent light over a wavelength of the fluorescentMewburn Reference: 008912990 light. These two extrema may correspond to first energy level and the second energy level. These two extrema may be split into three (two for other isotopes of N) individual Hyperfine states for NV- centres.

[0105] The controller can be implemented by a computer and / or can implement the data-processing steps of the methods described herein. The controller can read out the electrical or electronic signals generated by the optical sensor, convert them into a digital image and / or calculate an image of the physical quantity from the digital image and / or the electronic signals. The controller may include a processor and a memory which stores programs, algorithms, and / or software that are executed by the processor.

[0106] The data-communication of the controller with the excitation light source, the optical sensor, the microwave source, and / or the magnetic source may be provided by a wired connection or by a wireless connection. The controller may receive the electronic signals from the optical sensor and / or can control the excitation light source, the microwave light source, and / or the magnetic source. For example, the controller may control the wavelength and / or the intensity of the excitation light, the parameter of the microwave radiation, and / or the configuration of the device magnetic field.

[0107] The microwave radiation may be specified by a parameter set which refers to all parameters that can be used to characterise the physical properties of the microwave radiation. The parameter set may include the frequency, the intensity, the amplitude, polarisation, the phase of the microwave radiation, a duration of a microwave pulse, and / or a time delay between two microwave pulses. The parameter “amplitude” may include parameters for defining amplitude modulation (AM) of the microwave radiation. The amplitude modulation may be a (periodic) switch between amplitude zero and a predetermined value (e.g. microwave radiation on or off which may correspond to an amplitude modulation having a squared waveform).

[0108] As described above, for generating the image and / or for measuring the physical property of the sample, e.g. the electromagnetic field from the sample, a plurality of measurements is made whereby the first and / or the second frequency may be varied in various steps (e.g. for sweeping the frequency). Increasing the number of measurements can provide a reduction of an error in the generation of the image and / or in the measurement of the electromagnetic field.

[0109] The first and / or the second frequency can be varied within the first and / or second frequency ranges such that at least one or more of the varied frequencies interact and / or resonate with the energy levels as induced by the device magnetic field (as discussed, this may refer to transitions from or to the respective energy level). For example, the first frequency range refers to a variation of the generated microwave radiation in such a way that at least one of the varied first frequencies of the microwave radiation resonates with a transition from or to the first energyMewburn Reference: 008912990 level. Similarly, the second frequency range refers to a variation of the frequency of the generated microwave radiation in such a way that at least one of the varied second frequencies of the microwave radiations resonates with the second energy level (as discussed, this may refer to transitions from or to the respective energy level). For example, the microwave radiation is varied in a range around a frequency of the microwave radiation that corresponds to an energy gap associated with the first energy level or the second energy level.

[0110] The second frequency may be in the first frequency range or the second frequency range. If the second frequency is in the first frequency range, this may provide additional information on the fluorescence response of the colour centres in the first frequency range. In other words, the first and second frequencies provide two data points of the fluorescence response in the first frequency range. If the second frequencies are in the second frequency range, the simultaneous measurement in the first frequency range and a second frequency range may provide information on the fluorescence response of the colour centres at two different energy levels of the colour centres.

[0111] For example, the first and / or the second frequencies are varied over a frequency range that corresponds to a deviation of 1%, 5%, 10%, 15%, 20%, 25%, 30%, 40%, or 50% of the energy level of the first energy level or the second energy level. In some embodiments, the first frequency range and / or the second frequency range are chosen in that the recorded fluorescent light shows the entire peak or dip over the varied frequency. In other words, the recorded fluorescent light exhibits a baseline. Stated differently, the first frequency range and / or the second frequency range are chosen such that the fluorescent light is recorded in resonance with the first or second energy levels and off reference of the respective energy levels.

[0112] Optionally discrete values of the frequency in the first frequency range and / or the second frequency range may be used. For example, the first frequency range and / or the second parameter frequency may be divided into 10, 20, 50, 100, 200, 500, or 1000 (equally) spaced apart values of the frequency. Consequently, 10, 20, 50, 100, 200, 500, or 1000 measurements for the first frequency range and / or 10, 20, 50, 100, 200, 500, or 1000 measurements for the second frequency range are made. The number of measurements made in the first frequency range and / or the second frequency range may correspond to the sampling frequency in the first parameter range and / or the second parameter range.

[0113] If the second frequency is in the second frequency range, the overall number of measurements for sampling frequency in the first and second frequency range can be halved because the first frequency and the second frequency are simultaneously recorded. If the secondary frequency is in the first frequency range, the overall number of measurements is halved because two frequencies are simultaneously recorded in the first frequency range (i.e. the first frequency and the second frequency). The measurements for the first frequency range can be repeated for theMewburn Reference: 008912990 second frequency range in order to determine peaks or dips in the free fluorescence response in both the first frequency range and the second frequency range.

[0114] It is also possible that the individual values of the frequency in the first frequency range and / or the second frequency range may not be equally spaced apart from each other. Rather, more measurements are made close to the expected extremum in the first frequency range and / or the second frequency range compared to values of the frequency of expected to be further away from the expected extremum.

[0115] The first frequency range may not overlap with the frequency range. For example, the first frequency range is offset from the second frequency range. It is also possible that the first frequency range and the second frequency range are chosen to be so broad that they overlap.

[0116] The first frequency range and the second frequency range may each cover an energy level of the quantum sensors that is involved in the generation of the fluorescence light. For example, the first frequency range and the second frequency range correspond to different energy levels of the Hyperfine splitting and / or Zeeman splitting of the quantum sensors.

[0117] The first frequency may be offset from the second frequency to such a degree that the fluorescence light generated by the quantum sensor based on the interaction with the microwave radiation of the first frequency is not influenced by the interaction with the microwave radiation of the second frequency (and vice versa). In other words, the first frequency and the second frequency may be selected to provide independent readings of the quantum sensors. For example, the first frequency may not overlap with the second frequency and / or the first frequency may be offset from the second frequency by at least 1%, 2%, 3 %, 4%, 5 %, 7 % or 10 % of the first frequency or the second frequency.

[0118] The first frequency range, the second frequency range, the first frequency, and the second frequency may be predetermined or set before the measurement and / or may be selected with regard to the energy levels of the colour centres. For example, the first frequency range, the second frequency range, the first frequency, and the second frequency may be set after calibration of the quantum device. The first frequency range, the second frequency range, the first frequency, and the second frequency may be set with regard to the known energy levels.

[0119] The generation of the first frequency and the second frequency and the subsequent or simultaneous recording of the electronic signals may be executed during the measurement, i.e. for imaging and / or measuring a physical property. This means in some examples that the generation of the first frequency and the second frequency and the subsequent or simultaneous recording of the electronic signals are not executed for the calibration of the quantum device. Rather, the generation of the first frequency and the second frequency and the subsequent orMewburn Reference: 008912990 simultaneous recording of the electronic signals may be part of the measurement of the physical property.

[0120] Optionally, the calculation of the physical property is based on and / or uses the electronic signals that are recorded when the microwave radiation having the first frequency and the second frequency are generated. This can be understood that the generation of the microwave radiation having the first frequency and the second frequency is part of the determination and / or calculation of the physical property. The controller may be configured to record absolute values of the electronic signals for determining and / or calculating the physical property. This may mean that the quantum device is calibrated before the measurement (e.g. before the generation of the microwave radiation having the first frequency and the second frequency).

[0121] For each measurement and / or each recording of the electronic signals, the electrical signals received from each pixel are recorded. In other words, when a measurement is made using the first and second frequencies and / or during the recording of the electronic signals over the duration of the amplitude modulation, the electronic signals of all pixels are recorded, e.g. simultaneously recorded. Subsequently, a further measurement of the colour centres can be recorded using a different value of the first and / or second frequencies. Thus, for every value of the first and / or second frequencies of the microwave radiation, the intensities of the fluorescent light of the colour centres are (simultaneously) recorded over the duration of the amplitude modulation. It is to be noted that these measurements may not be displayed. Rather, the electronic signals of each measurement and for each pixel is further processed as described below.

[0122] The electronic signals for each pixel and / or each measurement include information on fluorescence response of the colour centres as induced by the first frequency and the second frequency. However, there is a single electronic signal for each pixel. In other words, the information on fluorescence response of the colour centres as induced by the first frequency and a second frequency needs to be extracted from the electronic signal. To this end, the information embedded by the amplitude modulation can be used to assign the fluorescence response of the colour centres with regard to the first frequency and the second frequency.

[0123] For example, each electronic signal or the electronic signals of one measurement can be analysed to attribute the obtained values to the fluorescence response induced by the first frequency and to the fluorescence response induced by the second frequency. For example, the electronic signals can be analysed with regard to the modulated amplitude of the microwave radiation having the first frequency and the modulated amplitude of the microwave radiation having the second frequency. Commonly known techniques for extracting amplitude information from a signal can be used.Mewburn Reference: 008912990 For example, each electronic signal or the electronic signals of one measurement can be Fourier-transformed and the peaks corresponding to the frequency of the amplitude modulation for the modulation of the first frequency and the frequency of the amplitude modulation for the modulation of the second frequency can be used as the extracted data (or data points) corresponding to the first frequency and the second frequency.

[0124] The extraction step may correspond to obtaining data from the electronic signals which indicate the fluorescence responses as induced by the microwave radiation having the first frequency and the microwave radiation having the second frequency. In this way, although the colour centres are simultaneously excited by two different frequencies of the microwave radiation, the fluorescence response can be deconvoluted or extracted from a single signal (the electronic signals) to obtain data indicating the fluorescence response of colour centres as manipulated using the first frequency and using the second frequency. In other words, after the extraction step, information or data is available as if two measurements were made sequentially, namely using the first frequency and then using a second frequency. In this way, the overall time for measuring the physical property of the sample can be reduced.

[0125] The extracted data can be used to identify changes in the fluorescence responses by the colour centres as induced by the first frequency and the second frequency. In one example, the extracted data corresponding to the first frequency is compared to the extracted data corresponding to the second frequency for identifying changes therein, for example the value of the extracted data points which may correspond to the intensity of the emitted fluorescent light. These changes may be used for determining the electromagnetic field from the sample, e.g. a direction and / or amplitude of the electromagnetic field. To this end, commonly known physical models of the colour centres and their interaction with the microwave radiation can be used.

[0126] In some examples, a plurality of measurements can be made in the first frequency range and in the second frequency range. For calculating the physical property, e.g. electromagnetic field, from the extracted data, the data points corresponding to the first frequency range can be compared to the data points corresponding to the second frequency range.

[0127] For example, changes in the extracted data points between the first frequency range and the second frequency range are determined. This means that the extracted data points over the first frequency range are compared to the extracted data points over the second frequency range. The comparison can be done by cross-correlating the extracted data points over the first frequency range with the corresponding extracted data points over the second frequency range. This process is repeated for every pixel. Thus, at the end of this process, changes in electronic signal for each pixel are determined. It is possible to generate an image and / or calculate the physical property of the sample, e.g. electromagnetic field from the sample, based on the changes of the electronic signals in each pixel.Mewburn Reference: 008912990

[0128] The determination of the changes in the extracted data points for each pixel may correspond to determining (frequency and / or amplitude) shifts between the extrema in first frequency range and the second frequency range. These shifts between the extrema in the first frequency range and the second frequency range can be detected by cross-correlating the extracted data points for the first frequency range with extracted data points for the second frequency range. In other words, the quantum device and the methods described herein may not refer to determining an absolute position of an extremum in the first frequency range and / or the second frequency range. Rather, the quantum device and the method described herein determine a shift in the extrema between the first frequency range and the second frequency range. This approach can be less error prone because no absolute position is determined. Rather a relative change is detected.

[0129] It is also possible to record for each pixel graphs, diagrams, and / or plots of the extracted data points (e.g. corresponding to the intensity of the fluorescent light emitted by the colour centres at the respective frequency of the microwave radiation) over the first frequency range and the second frequency range. The determination of the changes in the extracted data points may then cross-correlating the graphs, diagrams, and / or plots.

[0130] An extremum (e.g. a peak or dip) in the calculated cross-correlation may correspond to a difference, shift, or lag between two extrema of the first frequency range and the second frequency range. This difference, shift, or lag may be proportional to a strength of the electromagnetic field. However, other values of the calculated cross-correlation can be used for calculating the physical property, e.g. the electromagnetic field, as the Zeeman effect causing the split in the energy level depends on the strength of the physical property, e.g. the electromagnetic field, interacting with the colour centres.

[0131] The cross-correlation or certain values of the calculated cross-correlation may be connected to a value of the electromagnetic field. For example, shifts in the minimum or the maximum of the extracted data points (corresponding to the intensity of the fluorescent light) can thereby be attributed to particular interactions of the microwave radiation and / or the physical property, such as the electromagnetic field, with the sample. In other words, these changes in the values of the extracted data points correspond to changes in the interaction of the microwave radiation and / or the device magnetic field with the sample.

[0132] The plurality of simultaneous variations of the first frequency and the second frequency may correspond to the number of measurements over the first and / or second frequency ranges as outlined above. This means, each variation of the first frequency and the second frequency corresponds to changing the first frequency and the second frequency and taking a measurement, e.g. recording the intensity of the fluorescent light emitted by the colour centres.Mewburn Reference: 008912990 Then, the first frequency and the second frequency are again varied, for example by incrementally increasing the value of the frequency and the same measurement is repeated until all variations of the frequency within the first frequency range and the second frequency range are taken.

[0133] The first frequency and the second frequency may be varied or changed by the same amount, optionally for each measurement. However it is possible that the first frequency is changed differently compared to the second frequency. For example, a step size for the variation of the first frequency may be larger than a step size for the variation of the second frequency between two measurements. This may be helpful if there are differences in the range of the first frequency range and the second frequency range and an equal number of measurements are intended to be made within the first frequency range and the second frequency range.

[0134] It is possible that the electrical signals of all pixels for a single recording of the electronic signals are recorded in a format of a matrix. In this case, the calculation of the cross-correlation may include matrix multiplication or other types of calculation methods relating to matrices. In other words, the calculation of the cross-correlation is simultaneously done for all pixels. However, the electrical signals or extracted data points recorded by an individual pixel are only compared to electronic signals or extracted data points, respectively, of the same pixel. This means that the method described herein does not compare electronic signals or extracted data points from different pixels. As outlined above, the form or shape of the electrical signals or extracted data points over the varied frequency may differ from pixel to pixel due to the complex interaction of the colour centres with the external magnetic field and / or the generated microwave radiation. As such, a cross-correlation between electrical signals or extracted data points generated by different pixels may not result in useful information from the cross-correlation.

[0135] The cross-correlation is a non-parametric method. This means that the cross-correlation may be agnostic to the shape of the extracted data points over the frequency ranges. Thus, the crosscorrelation is capable of providing reliable results although the shape of the extracted data points over the frequency ranges can vary significantly between two pixels. It is assumed that the shape of the extracted data points over the frequency ranges between the first and second frequency ranges is similar or identical because the extracted data points are based on the same group of colour centres (i.e. from the same location and, therefore, subjected to the same electromagnetic field).

[0136] The cross-correlation function may be a discrete cross-correlation. An exemplary formula is given belowMewburn Reference: 008912990

[0137]

[0138] Thereby, f are the discrete extracted data points over the first frequency range, g are the discrete extracted data points over the second frequency range, n and m are the number of the varied frequencies, and N corresponds to the number of variations over the first frequency range and the second frequency range. Optionally, the number of variations in the first frequency range and the second parameter frequency is the same.

[0139] All measurements over the first frequency range and the second frequency range may be considered as corresponding to an optically detected magnetic resonance (ODMR) measurement. Further exemplary measuring techniques that can be used are coherently averaged synchronized readout (CASR) measurements or AERIS (Amplitude-Encoded Radio Induced Signal) method.

[0140] It is apparent from the above exemplary measuring techniques that not only the frequency of the microwave radiation is varied. Other parameters of the microwave radiation may be simultaneously and / or additionally varied or changed within the same measurements.

[0141] It is also possible that each recording of the electronic signal and / or each measurement is not only made in the first frequency range and the second frequency range. Rather, further frequency ranges may be measured wherein each frequency range can correspond to an energy level of the colour centres. For example, the first and second frequency ranges correspond to the energy levels of the colour centres that are induced by the component of an external magnetic field that extends in the x-direction. Third and fourth frequency ranges correspond to the energy levels of the colour centres that are induced by the component of an external magnetic field that extends in the y-direction. Fifth and sixth frequency ranges correspond to the energy levels of the colour centres that are induced by the component of an external magnetic field that extends in the z-direction.

[0142] A third frequency, e.g. in the third frequency range, may be simultaneously generated by the microwave source as the first and second frequencies. A fourth frequency, e.g. in the fourth frequency range, may be simultaneously generated by the microwave source as the first and second frequencies. A fifth frequency, e.g. in the fifth frequency range, may be simultaneously generated by the microwave source as the first and second frequencies. A sixth frequency, e.g. in the sixth frequency range, may be simultaneously generated by the microwave source as the first and second frequencies.Mewburn Reference: 008912990 In this example, it is possible to calculate the external magnetic field in each dimension in single measurement or a series of measurements by calculating the cross-section of corresponding frequency ranges. Further, a vector of the external magnetic field can be calculated from the calculated x-, y-, and z-components of the external magnetic field.

[0143] In this example, the six frequency ranges can be simultaneously measured by generating and amplitude-modulating the first to sixth frequencies. In this case, the overall measurement time can be reduced to a sixth. Of course, it is possible to simultaneously generate and amplitude-modulated more or less than the sixth frequencies as outlined above. For example, two, three or n frequencies (e.g. in the first to n-th frequency ranges) can be generated and amplitude-modulated resulting in a total of n simultaneously generated frequencies. In this case, the overall measurement time can be reduced by 1 / (n*6).

[0144] The axes of the colour centres may not be orthogonal to each other (for example, the axes of the NV centres are oriented tetrahedrally). In this case, the x-, y-, and z-components of the external magnetic field may be projections onto the non-orthogonal axes of the colour centres. Thus, the vector of the magnetic field is calculated by taking into account that the axes of the colour centres are not orthogonal to each other.

[0145] It is also possible that the first frequency range and / or the second frequency range cover two or more energy levels of the colour centres. In this case, the curve of the fluorescent light over the varied frequency includes two or more extrema (which each may include the Hyperfine states).

[0146] In an optional embodiment, the controller is configured to calculate the physical property of the sample by determining an extremum of the cross-correlation.

[0147] The extremum may be a peak (maximum) or a dip (minimum) of the cross-correlation. For example, the position of the peak in the cross-correlation corresponds to a frequency difference between extrema in the first frequency range and the second frequency range. For example, the curve or plot of the fluorescent intensity in each frequency range may include 1 , 2, 3 or more local maxima or minima (e.g. a triplet of peaks or dips corresponding to the Hyperfine states) . The maximum of the cross-correlation describes the frequency shift which is required to map the curve or plot of the first frequency range onto the curve or plot of the second frequency range. As outlined above, this difference in the frequency of corresponding extrema can be proportional to the external electromagnetic field. Hence, the difference in the frequency of corresponding extrema in the first frequency range and the second frequency range can be used to calculate a strength of an external electromagnetic field.Mewburn Reference: 008912990 The extremum in the cross-correlation can be determined by determining the maximum or minimum value in the entire range of the cross-correlation or in subsections thereof. In the latter case, a local extremum in the cross-correlation can be determined.

[0148] In some examples, the controller is configured to determine an extremum of the extracted data points in the first frequency range and an extremum of the extracted data point and the second frequency range. Optionally, the controller is configured to use the frequency corresponding to the determined extremum in the first frequency range and the determined extremum in the second frequency range for calculating the electromagnetic field. For example, as described in connection with the cross-correlation, the changes in the frequency of the extrema and / or the amplitude of the extrema may be indicative of the electromagnetic field.

[0149] In optional embodiment, the controller is configured to fit a curve to the extracted data points or the cross-correlation. Optionally, the controller is further configured to determine the extremum of the cross-correlation as the extremum of the fitted curve or the extremum of the extracted data points as the extremum of the extracted data points.

[0150] This approach may provide more reliable results for determining the extremum in the crosscorrelation and / or the extracted data points. For example, outliers that may have been identified as an extremum are not considered when determining an extremum of the fitted curve. The fitting of the curve with the cross-correlation and / or the extracted data points may be more reliable compared to fitting a curved to the extracted data points over the first frequency range and the second frequency range because less deviation from the expected shape or form of the curve is expected with cross-correlation compared to electronic signals. When fitting a curve to the cross-correlation, only a single curve needs to be fitted compared to fitting curves to the extracted data points with which two curves are fitted, namely the curves over the first frequency range and the second frequency range. The fitting of the curve to the crosscorrelation and / or the extracted data points may be done as known in the prior art.

[0151] In an optional embodiment, the quantum sensor device includes a diamond having negatively charged nitrogen vacancy (NV ) centres as colour centres and the first energy level and the second energy level correspond to a Zeeman shift induced by the device magnetic field.

[0152] As discussed above, NV centres are known to have good physical characteristics for generating fluorescent light depending on an external electromagnetic field. Further, reliable methods for manufacturing NV centres in diamonds are known.

[0153] The NV- defect in diamond consists of a substitutional nitrogen atom adjacent to a carbon vacancy. Its two unpaired electrons form a spin triplet in the electronic ground state (3A), the degenerate ms= ± 1 sublevels being separated from the ms= 0 level by 2.87 GHz at roomMewburn Reference: 008912990 temperature. The ms= 0 sublevel exhibits a high fluorescence rate when optically pumped. In contrast, when the defect is excited in the ms= ± 1 levels, it exhibits a higher probability to cross over to the non-radiative singlet state (1A) followed by a subsequent relaxation into ms= 0. As a result, the spin state can be optically read out, the ms= 0 state being “bright” and the ms= ± 1 states being dark. When an external magnetic field is applied, the degeneracy of the spin sublevels ms= ± 1 is broken via Zeeman splitting. This causes the resonance lines to split depending on the applied device magnetic field magnitude and its direction. This dependency can be used for vector magnetometry as the resonant spin transitions can be probed by sweeping the microwave (MW) frequency resulting in characteristic dips in the optically detected magnetic resonance (ODMR) spectrum. As described above, the magnetic source may also be configured to vary a configuration of the device magnetic field. This may be used for the vector magnetometry.

[0154] In an optional embodiment, the controller is further configured to use a discrete Fourier-transformation, optionally a Fast-Fourier-transformation ora Nonuniform Fast-Fourier-transformation, for calculating the cross-correlation and / or for extracting the data from the electronic signals.

[0155] For example, the Fast-Fourier-transformation uses the Cooley-Tukey algorithm. The calculation of the cross-correlation may make use of the cross-correlation theorem which states that the cross-correlation between two signals is equal to the product of Fourier transformation of one signal multiplied by complex conjugate of Fourier transformation of another signal. Thus, in one embodiment, the cross-correlation is calculated by Fourier-transform the electronic signals from the first frequency range and multiply the Fourier-transformed signals with the complex conjugate of the Fourier-transformation of the electronic signals from the second frequency range. To this end, fast Fourier transformation as outlined above can be used. This allows to further reduce the computing resources and / or the computing time.

[0156] In an optional embodiment, the controller is configured to control the microwave source to modulate the microwave radiation having the first frequency with a first modulation frequency and to modulate the microwave radiation having the second frequency with a second modulation frequency which is different to the first modulation frequency.

[0157] In this way, the amplitude modulation of the first frequency can be distinguished from the amplitude modulation of the second frequency. Optionally, the ratio of the first modulation frequency to the second modulation frequency is greater than 10 %, 20%, 25%, 50 %, 75 %, 100 %, 150 %, or 200 % when the second modulation frequency is higher than the first modulation frequency. Generally, the larger the difference between the first modulation frequency and the second modulation frequency is, the easier it gets to extract the data points corresponding to the first frequency and the data points corresponding to the second frequencyMewburn Reference: 008912990 from the electronic signals. For example, peaks in the Fourier-transformation of the electronic signals are clearly separate from each other.

[0158] In some examples, only one of the microwave radiation having the first frequency and the microwave radiation having the second frequency is amplitude-modulated. The amplitude-modulated microwave radiation is extracted as described above. The non-modulated microwave radiation can be extracted by subtracting the extracted data corresponding to the amplitude-modulated microwave radiation from the electronic signals as received from the optical sensor.

[0159] In an optional embodiment, a first modulation ratio of the first modulation frequency to the first frequency is a prime number and / or a second modulation ratio of the second modulation frequency to the second frequency is a prime number.

[0160] If the first ratio and / or the second ratio are prime numbers, crosstalk between the amplitude modulation of the first frequency and the amplitude modulation of the second frequency can be reduced or avoided entirely because the amplitude modulation of the first frequency is not a multiple or a factor of the amplitude modulation of the second frequency and / or of the Alias signals beyond the Nyquist frequency, for example if there is a non-linear response of the colour centres. In this case, a Fourier analysis of the electronic signals does not include peaks that belong to electronic signals corresponding to the first frequency and the second frequency.

[0161] In an optional embodiment, the controller is configured to vary the first frequency and the second frequency for sweeping the first frequency in the first frequency range and the second frequency in the first frequency range or the second frequency range. Optionally, the controller is further configured to repeat items (i) to (iv) for each varied first frequency and second frequency. Further optionally, with item (v), the controller is configured to determine an extremum in the data corresponding to the first frequencies and an extremum in the data corresponding to the second frequencies, and calculate the physical property of the sample using the extrema.

[0162] A measurement may correspond to items (i) to (iii) i.e. that the controller is configured to control the microwave source to simultaneously generate microwave radiation having the first frequency and microwave radiation having a second frequency, control the microwave source to modulate the amplitude of the microwave oration having a first frequency and the map microwave radiation and the second frequency, and record, for each pixel, the electronic signals received from the optical sensor for the modulated amplitude of the microwave radiation having a first frequency and microwave radiation having a second frequency, optionally for each variation of amplitude of the microwave radiation. In item (iii), a plurality of electronic signals isMewburn Reference: 008912990 recorded, wherein each electronic signal (for each pixel) corresponds to a step in the amplitude modulation or an amplitude range in the amplitude modulation.

[0163] Item (iv) may correspond to a data analysis step or data processing step in which data corresponding to the first frequency and the second frequency is extracted from the electronic signals for each pixel and using the one or more modulation frequencies. Item (iv) may be executed after each measurement or when all measurements are completed.

[0164] As outlined above, the measurement as outlined above is repeated with a varied first frequency and a varied second frequency for sweeping the first frequency range and / or the second frequency range. In other words, with this example, the fluorescence response of the colour centres is measured depending on the frequency.

[0165] The calculation of the physical property is based on the extracted data. For example, each measurement includes a data point corresponding to the first frequency and a data point corresponding to the second frequency. The data points are analysed as outlined above for determining or calculating the physical property, e.g. the electromagnetic field.

[0166] In an optional embodiment, the controller is configured to simultaneously generate a plurality of first frequencies in the first frequency range and a plurality of second frequencies in the first frequency range and / or the second frequency range. Optionally, with item (iv), the controller is configured to extract - for each pixel and using the one or more modulation frequencies - data corresponding to each one of the first frequencies and to each one of the second frequencies from the electronic signals. Further optionally, with item (v), the controller is configured to determine an extremum in the data corresponding to the plurality of the first frequencies and an extremum in the data corresponding to the plurality of the second frequencies, and calculate the physical property using the extrema.

[0167] With this example, the multiple measurements for sweeping the first frequency range and / or the second frequency range can be replaced by a single measurement in which a plurality of (first) frequencies in the first frequency range and a plurality of (second) frequencies in the second frequency range are simultaneously generated. Each frequency of the plurality of first and second frequencies can be modulated with a modulation frequency wherein each modulation frequency is different to any other modulation frequency.

[0168] For example, if hundred measurements are made for sweeping the first frequency range and the second frequency range (i.e. the first frequency and a second frequency are varied hundred times), this can be replaced by hundred first frequencies and second frequency that are simultaneously generated and modulated. This significantly reduces the measurement timeMewburn Reference: 008912990 compared to 200 measurements (100 for the first frequency range and 100 for the second frequency range) that would need to be made with commonly known methods.

[0169] In some examples, the first frequency and / or the second frequency is not varied (swept).

[0170] Rather, a plurality of the first frequencies and a plurality of the second frequencies are simultaneously generated and modulated as described above. Of course, it is also possible to simultaneously generate and modulate a plurality of the first frequencies and the plurality of the second frequencies as a first measurement and vary the plurality of first frequencies and the plurality of second frequencies in one or more subsequent measurements.

[0171] In an optional embodiment, the controller is configured to (I) control the microwave source to simultaneously generate a microwave radiation having a first frequency set and a microwave radiation having a second frequency set, the first frequency set being in the first frequency range and including the first frequency and one or more additional first frequencies, and the second frequency set being in the first frequency range or the second frequency range and including the second frequency and one or more second additional frequencies, (II) control the microwave source to modulate - using the one or more modulation frequencies - the amplitudes of the microwave radiation having the first frequency set and the microwave radiation having the second frequency set, (III) record - for each pixel - the electronic signals received from the optical sensor for the modulated amplitudes of the microwave radiation having the first frequency set and the microwave radiation having the second frequency set, (IV) extract - for each pixel and using the one or more modulation frequencies - data corresponding to the first frequency set and the second frequency set from the electronic signals, and / or (V) calculate the physical property using the extracted data corresponding to the first frequency set and the second frequency set.

[0172] In an optional embodiment, the controller is configured to vary the first frequency set and the second frequency set for sweeping the first frequency set in the first frequency range and the second frequency set in the first frequency range or the second frequency range. Optionally, the controller is further configured to repeat items (I) to (IV) for each varied first frequency set and second frequency set. Further optionally, with item (V), the controller is configured to determine an extremum in the data corresponding to the first frequencies and an extremum in the data corresponding to the second frequencies, and / or calculate the physical property using the extrema.

[0173] The first frequency set may include two, three, four, or more first frequencies and / or the second frequency set may include two, three, four, or more second frequencies. The first frequency set and / or the second frequency set may be considered a frequency comb. The first frequency set and the first second frequency set can be swept over the first frequency range and / or the second frequency range, respectively. This means that all first frequencies of the first frequencyMewburn Reference: 008912990 set are varied between measurements and / or all frequencies of the second frequency set are varied between measurements (similar to the variation of the first frequency and the second frequency as outlined above).

[0174] Sweeping the first frequency set over a triplet of energy states may result in a recorded curve over the first frequency range that exhibits five extrema. This is because the recorded curve over the first frequency range is a convolution of the first frequency set over the triplet of energy states.

[0175] Optionally, the difference between the first frequencies of the first frequency set may correspond to the difference in the frequencies of the triplet in the first frequency range.

[0176] Similarly, the difference between the second frequencies of the second frequency set may correspond to the difference in the frequencies of the triplet in the second frequency range. If so, the greatest peak or dip (the greatest extremum) may have a larger amplitude compared to a situation where a single first frequency and / or a single second frequency is swept over the triplet in the first frequency range and / or the second frequency range, respectively. Thus, using a first frequency set and / or second frequency set can increase the contrast of the calculated electromagnetic field.

[0177] It is to be noted that the first frequencies of the first frequency set and / or the second frequencies of the second frequency set do not need to be modulated for calculating the electromagnetic field. Rather, the electronic signals can be deconvoluted because the electronic signals are a convolution of the first frequency set with the triplet in the first frequency range and / or a convolution of the second frequency set with the triplet in the second frequency range.

[0178] The calculation of the physical property, e.g. the electromagnetic field, when using a first frequency set and / or the first second frequency set can be done similarly to the calculation of the physical property, e.g. the electromagnetic field, when using the first frequency and / or second frequency. In other words, cross correlations can be calculated between the data points over the first frequency range and the second frequency range and / or curves can be fitted to the data points over the first frequency range and / or the second frequency range for determining extrema in the curves over the first frequency range and / or the second frequency range. The position (frequency) and / or the amplitude of the extrema can be used to calculate the physical property, e.g. the electromagnetic field, as commonly known.

[0179] In some examples, the first frequencies in the first frequency range have the same first modulation frequency of the amplitude modulation and / or the second frequencies in a second frequency range have the same second modulation frequency of the amplitude modulation. In this way, the number of different frequencies for the amplitude modulation can be reduced whileMewburn Reference: 008912990 still allowing to extract the data points from the electronic signals, e.g. calculating the physical property from the electronic signals.

[0180] Optionally, frequency differences between the first frequencies of the first frequency set are constant when varying the frequency of the first frequencies of the first frequency set. In other words, a difference between two frequencies of the first frequency set does not change when the first frequencies of the first frequency set are varied between measurements. Similarly, frequency differences between the second frequencies of the second frequency set can be constant when varying the frequency of the second frequencies of the second frequency set.

[0181] In an optional embodiment, for providing a reference of the noise of the excitation light source, the controller is configured to control the microwave source not to emit microwave radiation and to record - for each pixel - reference electronic signals received from the optical sensor.

[0182] Optionally, the controller is configured to - for each pixel - calculate a ratio of the recorded electronic signals and the reference electronic signals. Further optionally, with item (iv), the controller is configured to extract - for each pixel and using the one or more modulation frequencies - data corresponding to the first frequency and the second frequency using the calculated ratio.

[0183] In this embodiment, the electronic signals are recorded without microwave radiation being emitted onto the colour centres. The excitation light source emits the excitation light for recording the fluorescence response of the colour centres without being excited and / or manipulated by the microwave radiation. The electronic signals recorded without the emission of the microwave radiation can be regarded as reference electronic signals which can be indicative of noise (e.g. laser noise), drift (e.g. a thermal drift within the quantum device), and / or other sources of measurement artefacts.

[0184] The reference electronic signals can be used for referencing the noise within the electronic signals. The electronic signals include the reference electronic signals and fluorescence response of the colour centres. By referencing the electronic signals with the reference electronic signals, the share and / or proportion of noise within the electronic signals can be reduced and / or eliminated. For example, the electronic signals are divided by the reference electronic signals. Of course, other means for referencing the electronic signals to the reference electronic signals can be used. For example, the logarithm of the reference electronic signals can be subtracted from the logarithm of the electronic signals and the result is input in an exponential function.

[0185] The referencing of the electronic signals is done for each pixel and / or pixel-wise. For example, the electronic signal from a particular pixel is divided by the reference electronic singles from the same pixel. This can be done for all pixels or for a subset of pixels which are consideredMewburn Reference: 008912990 relevant for the measurement. Further, each electronic signal can be referenced to an average reference electronic signal or a particular subset of reference electronic signals.

[0186] The electronic signals that have been referenced to the reference electronic signals for reducing the noise in the electronic signals are then used for extracting the data corresponding to the first frequency and the second frequency. This means that the referencing is executed prior to the extraction of the data from the electronic signals.

[0187] The microwave source may be configured to stop generating the microwave radiation during the recording of the reference electronic signals. Alternatively or additionally, the microwave source includes a switch between the microwave antenna and the microwave generator which is configured to disconnect the microwave antenna from the microwave generator during the recording of the reference electronic signals. This means that the microwave generator continuously generates the microwave radiation irrespective of a reference measurement or a measurement for recording the electronic signals.

[0188] The reference electronic signal can be generated for each recording of the electronic signals and / or for each measurement. For example, the reference recording (i.e. recording the reference electronic signals) may alternate with a recording of the electronic signals. Optionally, the reference recording can be executed before or after a recording of the electronic signals. Of course other patterns are possible. For example, the reference recording is executed every second, third, fourth, etc recording of the electronic signals. It is also possible to record the reference electronic signals between two measurements (e.g. when the frequency is varied).

[0189] Reducing the number of reference recordings reduces the overall time for recording the electronic signals required for calculating the electronic signals. On the other hand, increasing reference recordings can reduce the noise and / or increase the contrast of the calculation of the physical property because external factors such as laser noise can be reduced.

[0190] In an optional embodiment, for providing a reference of the noise of the excitation light source, the controller is configured to - for each pixel - calculate a reference ratio of the electronic signal corresponding to the first frequency and the electronic signal corresponding to microwave radiation having the first frequency and the second frequency and the electronic signal corresponding to microwave radiation having the varied first frequency and the varied second frequency and / or a varied amplitude. Optionally, with item (iv), the controller is configured to extract - for each pixel and using the one or more modulation frequencies - data corresponding to the first frequency and the second frequency using the reference ratio.

[0191] With this embodiment, the referencing is not executed with regard to a reference recording as outlined above. Rather, the referencing is done between two recordings of the electronicMewburn Reference: 008912990 signals. Both embodiments can be combined or used alternatively as necessary. For example, every fourth, fifth, sixth, etc recording, a reference recording is inserted and all other recordings are referenced to the previous or subsequent recording.

[0192] The referencing between two recordings can be done by referencing the electronic signals for a particular pixel with the electronic signal for the same pixel, whereby the electronic signals are recorded for two different values of the first frequency and / or the second frequency. For example, if the first frequency and / or the second frequency is swept over the first frequency range and / or the second frequency range, respectively, two subsequent recordings include the electronic signals for two different first frequencies and / or second frequencies.

[0193] Alternatively or additionally, the referencing between two recordings can be done by referencing the electronic signals for a particular pixel with the electronic signal for the same pixel, whereby the electronic signals are recorded for two different values of the amplitude modulation. For example, two subsequent recordings of the amplitude modulation include the electronic signals for two different values of the amplitude as outlined above.

[0194] Similar to the reference recordings, the electronic signals of the first recording can be divided by the electronic signals of a second subsequent recording. Again, this may reduce or eliminate the share and / or proportion of the noise within the electronic signals. Further, since reference recordings can be avoided, the number of overall recordings can be reduced which reduces the overall time for obtaining the electronic signals necessary for calculating the electromagnetic field.

[0195] Similar to the reference recording, the data is extracted from the referenced electronic signals, e.g. the reference ratio. The reference ratio may be calculated by dividing - for each pixel - the electronic signal from a particular pixel obtained during the generation of the first / second frequency and / or a first value of the amplitude modulation by the electronic signal from the same pixel obtained during the generation of a varied first / second frequency (e.g. the frequencies are in the first / second frequency ranges and different to the first / second frequencies, for example larger or smaller) and / or for different values of the amplitude modulation.

[0196] In an optional embodiment, the controller is configured to calculate baselines of the electronic signals in the first frequency range and the second frequency range. Optionally, the controller is further configured to subtract the respective calculated baseline from electronic signals in the first frequency range and the second frequency range prior to calculating the cross-correlation.

[0197] The baseline of the electronic signals in the first frequency range and the second frequency range may correspond to values of the recorded intensity of the fluorescent light at which theMewburn Reference: 008912990 varied parameter is off resonance with the first energy level and the second energy level, respectively. Thus, the baseline may correspond to a range of values of the varied parameter at which the interaction of the microwave radiation does not resonate with the first energy level and / or the second energy.

[0198] The calculation of baselines in a curve, plot, or dataset is commonly known and can be appropriately used for calculating the baseline in the first frequency range and / or the second frequency range. A value of the calculated baseline may be subtracted from all electronic signals in the first frequency range and / or the second frequency range. This may correspond to a normalisation of the electronic signals in the first frequency range and / or the second frequency range. This provides better comparison (e.g. for the cross-correlation) between the electronic signals from the first frequency range and the second frequency range because they do not differ in their respective baselines.

[0199] In an optional embodiment, the controller is configured to smooth and / or upsample the electronic signals in the first frequency range and / or the second frequency range prior to calculating the cross-correlation.

[0200] The smoothing or upsampling of the electronic signals may be done prior to calculating the cross-correlation and / or for increasing the reliability and / or sensitivity of the cross calculation and, therefore, of the calculation of the electromagnetic field.

[0201] The smoothing of the signals in the first frequency range and / or the second frequency range may be implemented by using derivative filters and / or boxcar mean filters. Examples of these filters are Savitzky-Golay or Norris filters / derivatives. These filters can dampen the noise in the electronic signals from the first frequency range and / or the second frequency range. As a result, the noise in the cross calculation can also be reduced.

[0202] The upsampling is done to increase the number of data points in the first frequency range and / or the second frequency range. Upsampling may also be implemented to adjust a sampling frequency in the first frequency range to the sampling frequency in a second frequency range or vice versa. The upsampling may be implemented by interpolating the electronic signals in the first frequency range and / or the second frequency range. Commonly known upsampling techniques and / or methods can be used.

[0203] In an optional embodiment, the controller is configured to execute a neural network which is trained to enhance extrema and / or remove noise in the electronic signals in the first frequency range and / or the second frequency range prior to calculating the cross-correlation.Mewburn Reference: 008912990 Commonly known neural networks can be used. The neural networks can be trained with data that is obtained by running measurements similar to the ones described herein. For example, the neural network is fed with data in which the frequency is varied in the first frequency range and the second frequency range, for example using the same sampling frequency. In this case, the neural network may be configured to enhance the extrema in the first frequency range and / or the second frequency range and / or remove the noise in electronic signals. Of course, other parameters of the microwave radiation may be varied and used fortraining the neural network.

[0204] The use of the neural network may optimise the signal-to-noise ratio which increases the sensitivity and / or accuracy of the cross-correlation, and therefore, the sensitivity and accuracy of the calculated electromagnetic field.

[0205] In an optional embodiment, the controller is a field-programmable gate array (FPGA) or an application-specific integrated circuit (ASIC).

[0206] The use of the FPGA or the ASIC can be possible because no curves are fitted to the electronic signals in the first frequency range and / or the second frequency range which often requires long algorithms and / or high computing power. These conditions may not be provided by the FPGA or the ASIC. However, with the controller and / or the method described herein, cross-correlation is used which requires shorter algorithms and less computing power compared to the commonly known techniques. These calculations can be implemented with the FPGA or the ASIC.

[0207] The use of FPGA or the ASIC may require less space compared to a regular computer which may provide the possibility to arrange the controller in line with the manufacturing line. For example, the method described herein can be used to image metallic structures in optically non-transmissible material (such as deep metallization layers in semiconductor circuitry). The semiconductor circuitry may be imaged in line, e.g. in a production line. If so, this may require implementing the controller as an FPGA or ASIC.

[0208] FPGA or the ASIC can be used for the controller when the controller and / or the quantum device are used in a production line, for example a production line for manufacturing chips and / or other types of semiconductor circuitries.

[0209] Chips, microchips, computer chips, integrated circuits (IC), or other types of semiconductor circuitries are examples of the sample whose manufacturing process can be controlled using the method described herein. Thus, the semiconductor circuitries are examples for the sample whose electromagnetic field can be imaged and / or measured using the quantum device and / or the methods described herein.Mewburn Reference: 008912990 In an optional embodiment, the method of imaging and / or measuring a physical property, optionally the physical property of the sample, is executed in real-time. Optionally, one or more of the following steps are executed in real-time: controlling a microwave source for simultaneously generating a microwave radiation having a first frequency and a microwave radiation having a second frequency, the first frequency being in a first frequency range in which the first energy level resonates with the microwave radiation, and the second frequency being in the first frequency range or a second frequency range in which the second energy level resonates with the microwave radiation, modulating - using one or more modulation frequencies - the amplitudes of the microwave radiation having the first frequency and the microwave radiation having the second frequency, recording - for each pixel of the optical sensor - the electronic signals received from the optical sensor for the modulated amplitudes of the microwave radiation having the first frequency and / or the microwave radiation having the second frequency, extracting - for each pixel and using the one or more modulation frequencies - data corresponding to the first frequency and the second frequency from the electronic signals, and calculating the physical property of the sample using the extracted data corresponding to the first frequency and the second frequency which may include determining -for each pixel - changes in the electronic signals by cross-correlating the electronic signals generated over first frequency range with the electronic signals generated over the second frequency range, calculating the physical property of the sample based on the cross-correlation.

[0210] Realtime calculations of the physical property, e.g. the electromagnetic field, may be possible by using the cross-correlation as described above and / or reducing the number of measurements by simultaneously generating microwave radiation including two or more frequencies as outlined above.

[0211] The term “real-time” may refer to a maximum duration for imaging and / or measuring the physical property (e.g. including recording electronic signals and analysing the recorded electronic signals for calculating the physical property), optionally the one or more steps outlined above, of 1 s, 5 s, 10 s or 100 s. Thereby, the time for calculating the physical property may be 0.1 s, 0.5 s, 1 s, 5 s, 10 s or 100 s.

[0212] Alternatively or additionally, the term “real-time” may refer to the speed of imaging and / or measuring a physical property of the sample, optionally as outlined above, such that it is possible to generate the image and / or the measurement of the physical property of the sample for inline measurements. This can mean that the sample is imaged and / or measured without removing the sample from a production line. Thus, the time for imaging and / or measuring the sample needs to be sufficiently short such that the manufacturing process of the sample is not halted, stopped, or paused for imaging and / or measuring the physical property of the sample.Mewburn Reference: 008912990 The imaged and / or measured physical property of the sample can be used to determine the quality of the sample which can be quantified using one or more quality parameters. The quality parameter may refer to the strength and / or orientation of the electromagnetic field, optionally depending on the respective location. The one or more quality parameter may indicate if the analysed sample includes sections of sufficient size, thickness, orientation, and / or location which generate and / or interact with an external electromagnetic field. These sections may correspond to metallization layers. Thus, the quality or quality parameter may provide a measure for assessing the correct manufacturing of the metallization layers inside the sample. Of course, the method is not limited thereto. Imaging and / or measuring the physical property of the sample can be used to determine different types of structures within the sample.

[0213] The sample may be considered fulfilling the desired quality if the one or more quality parameters are within respective one or more predetermined ranges. For example, if the quality parameter is below a certain lower threshold and / or above a certain upper threshold, this may be considered fulfilling the quality. The quality parameter may be determined for the entire sample, for predetermined sections of the sample, or for each pixel. In other words, there may be a plurality of quality parameters with associated predetermined range for assessing the quality of the sample, each quality parameter or set of quality parameters can be used to assess the quality of the sample in a respective zone of interest.

[0214] The determination of the quality may be executed in real-time as well. The entire method for determining a quality of a sample may be executed in real-time.

[0215] In an optional embodiment, the method for determining a quality of a sample may further include the step on executing a further step based on the determined quality of the sample. For example, the further step is automatically executed after the quality of the sample has been determined. Examples of the further step are described in the following.

[0216] If the quality of the sample is acceptable (e.g. if one, more, or all quality parameters are within their respective predetermined ranges), the controller may be configured to generate an acceptance signal. The acceptance signal may be associated with the respective sample and / or stored in the memory. The acceptance signal indicates that the respective sample fulfils the desired quality.

[0217] In an optional embodiment, the method further comprises rejecting the sample if the sample does not conform to the determined quality and / or generating a feedback signal based on the determined quality for changing the manufacturing process of the sample.

[0218] This optional embodiment may also be provided by the quantum device and / or the controller.Mewburn Reference: 008912990 A rejection signal may be generated if the quality of the sample is not acceptable (e.g. if one, more, or all quality parameters are outside their respective predetermined ranges). The rejection signal may be supplied to the manufacturing line and / or to associated machinery. For example, the receipt of the rejection signal by a control component may prompt the control component to remove the respective sample from the production line.

[0219] Alternatively or additionally, a feedback signal may be generated if the quality of the sample is not acceptable (e.g. if one, more, or all quality parameters are outside their respective predetermined ranges). The feedback signal may be supplied to the manufacturing line and / or the associated machinery. The feedback signal may be used to adjust and / or change certain process parameters of the production line and / or the manufacturing process.

[0220] The acceptance signal, the rejection signal, and / or the feedback signal may be generated by a neural network which is trained to determine the respective signals and / or the quality of the sample. For example, the neural network is part of the controller and / or the quantum device. The neural network may be configured to assess the imaged and / or measured physical property of the sample based on the trained / learned imaged and / or measured electromagnetic fields of the samples. For example, the neural network or the controller can compare the imaged and / or measured sample with a validated sample for assessing the quality and / or determining the quality parameter.

[0221] The method, quantum device, and / or controller described herein can be used to control errors in a manufacturing process. Optionally, this can be done inline due to the high speed of measuring and / or calculating the physical property of the sample.

[0222] The sample may be a certain type of cell (e.g. a cancerous cell), of bacteria, and / or of virus. In this case, the quality or quality parameter may refer to features of the respective biological material which indicates the type of the biological material. For example, the quality or quality parameter may distinguish a cancerous cell from a non-cancerous cell. Thus, the method, quantum device, and / or controller described herein can be used to (automatically) quantify and / or determine biological material, e.g. in a solution.

[0223] An example of the invention is described in the following:

[0224] The methods and devices described herein refer to the reduction of the overall measurement time by combining two or more measurements of different frequencies in a single measurement. For determining the electromagnetic field with known instruments, all frequency ranges (optionally six - corresponding to the three pairs of triplets for each direction) are scanned one by one. If it takes X time to measure one frequency range, the total time for known instrumentsMewburn Reference: 008912990 is 6*X (a fourth domain may also be present in which cash the total time is 8*X; the four domains may relate to the 4 orientations of the NV- centres). This implies that if the known instruments exhibit drifts (or, more generally, changes) in the time-domain (e.g. thermal heating / expansion) that impact the spectral appearance of the measurement, systematic errors to the obtained ESR spectrum would be introduced which may further extend the overall measurement time.

[0225] By applying frequencies from multiple frequency ranges at once, i.e. multiplexing them, it is possible to speed up the measurement by a factor of six (or, more generally, the number of multiplexed frequencies), reducing the total measurement time to X. The information from various multiplexed frequencies is separated by modulating the amplitude of each of the frequencies at a different modulation frequency over several (e.g. 100) images / frames and then extracting the individual data points in the frequency domain.

[0226] This method of measuring, for which an amplitude-modulated signal that is a sum of sine functions is recorded, enables the removal of the reference recordings that usually take place every other recording with known instruments. Due to the optional sinusoidal behaviour of the amplitude modulation, it is possible to reference neighbouring frames, effectively creating a derivative of the actual sinusoidal signal. This will now be a cosine instead of a sine, but will contain all the information and with the noise removed. In addition, it is possible to drop every second recording, which is commonly used with known instruments and contains a reference without actual information of the sample. This will speed up the overall measurement time by a factor of two.

[0227] In addition, it is possible to use a similar technique to increase the contrast (and therefore the sensitivity, i.e. “information gained per time”) by a factor of three. Each NV-state contains three (two for other isotopes of N) individual Hyperfine states. When a single frequency is swept over one of these ranges, each Hyperfine state will be visible with a contrast C. By using three multiplexed frequencies with the correct relative position and sweeping those instead, a maximum contrast of 3*C can be theoretically achieved when in perfect resonance.

[0228] With these optional aspects of the invention, it is possible to drastically speed up the measurement time. A measurement speedup 6*32*2 = 108 is possible (6 is one example; theoretically any number > 1 is feasible). This means if 1.5 h were necessary for a dataset with a known instrument, the same data having the same quality can be obtained in 50 seconds.

[0229] In addition, artefacts produced by long measurement times can be removed or reduced. One example of such an artefact would be caused by temperature drift. The information is usually obtained from the relative distances of pairs of resonances, a magnetic field leads to a relativeMewburn Reference: 008912990 shift of a pair, whereas temperature changes lead to a common mode shift. When measuring all resonances sequentially, a temperature drift can occur during the measurement of the first resonance of a pair and the second resonance of a pair. This would then change the relative distance of the two and therefore be detected as a change in the magnetic field.

[0230] The following lists optional features of the invention:

[0231] • Multiple frequencies applied to the NV-centres at the same time

[0232] • with a relative spacing such that all hyperfine resonances are hit under optimal conditions (~3 MHz)

[0233] • With relative frequencies, that all +-1 quantum states of all or a subset of NV directions can be addressed under ideal conditions

[0234] • amplitude modulating all or a subset of frequencies at different modulation frequencies • Sweeping this modulation scheme once, simultaneously over all frequency ranges • Extracting the amplitudes of the modulations for each step, e.g. using a Fast Fourier- Transformation

[0235] • OR, use a complete multiplexing scheme that does not perform sweeps but measures all microwave frequencies in parallel

[0236] • The modulation can be piecewise constant (during the frame of a camera)

[0237] • It is possible to remove the reference measurement and remove the laser noise by referencing neighbouring data points.

[0238] • It is possible to increase the number of frequencies to an arbitrary amount (at some point engineering becomes challenging) speeding up the measurement accordingly.

[0239] BRIEF DESCRIPTION OF THE DRAWINGS

[0240] The invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which:

[0241] Fig. 1 shows a schematic view of a quantum device;

[0242] Fig. 2 shows a block diagram for a method for determining a quality of a sample which includes a method for measuring an electromagnetic field from a sample using the quantum device of Fig. 1 ;

[0243] Fig. 3 shows a block diagram for a method for operating a controller of the quantum device of Fig. 1 for measuring an electromagnetic field from a sample and for determining a quality parameter of the sample;

[0244] Fig. 4 shows an exemplary graph of electronic signals recorded by the quantum device of Fig.

[0245] 1 when a frequency set of three frequencies is swept over a triplet of Hyperfine states;Mewburn Reference: 008912990

[0246] Fig. 5 shows a graph corresponding to extracted data points from electronic signals recorded by quantum device of Fig. 1 when six frequency sets each including three frequencies are simultaneously generated, amplitude modulated, and swept over a triplet of Hyperfine states; and

[0247] Fig. 6 shows an upper diagram depicting the temporal behaviour of exemplary amplitudes of six modulated frequencies (whereby a reference recording is made between the variation of the amplitudes wherein no microwave is emitted) and a lower diagram depicting the temporal behaviour of exemplary amplitudes of six modulated frequencies (whereby no reference recordings are made).

[0248] The figures are not drawn to scale. Throughout the description, similar parts have been assigned the same reference numerals, and a detailed description is omitted for brevity.

[0249] DETAILED DESCRIPTION

[0250] Fig. 1 shows an embodiment of a quantum device 10 for imaging a sample 12 and / or measuring a physical property of the sample 12, such as an electromagnetic field from or inside the sample 12. The magnetic field from the sample 12 may be the response of the sample 12 to an external electromagnetic field and / or to external stimulation. For example, the electromagnetic field from the sample 12 can be measured using the quantum device 10 may include NMR signals.

[0251] The quantum device 10 comprises a sample holder 16, a quantum sensor device 18, a microwave source 20, a magnetic source 22, a controller 24, optics 28, an excitation light source 30, and / or an optical sensor 32. The sample holder 16 is configured to support the sample 12. Further, in this example, the sample holder 16 further supports the quantum sensor device 18 such that the sample 12 is in direct contact with the quantum sensor device 18.

[0252] The sample 12 may be an integrated circuit, a printed circuit board, an electric device and / or material interface. These types of samples 12 may be imaged using the quantum device 10. For example, metallic structures may be imaged by detecting the magnetic field emitted or manipulated by the metallic structures. Alternatively, the sample 12 includes particles interacting with an external magnetic field. The variation in the external magnetic field caused by the particles in the sample 12 may be detected using the quantum device 10.

[0253] The optics 28, the excitation light source 30, and / or the optical sensor 32 may provide a wide-field microscope 14 which may additionally comprise a beam splitter 26.

[0254] The quantum sensor device 18 includes a substrate made of single-crystal diamond which contains a plurality of negatively charged nitrogen-vacancy (NV-) centres (examples of quantum sensors). The NV- centres can be projected onto the optical sensor 32 by the optics 28 whichMewburn Reference: 008912990 may include an objective. In other words, the wide-field microscope 14 allows the NV- centres to be projected onto the optical sensor 32 by means of wide-field imaging. The optical sensor 32 converts incident light into spatially resolved electrical or electronic signals which may be used when imaging the sample 12. For example, the optical sensor 32 comprises a plurality of pixels, each pixel generating an electrical or electronic signal indicative of an intensity and / or a wavelength of the light impinging on the respective pixel. The plurality of electrical or electronic signals for each pixel can thus be used to image the sample 12. This can be done by the controller 24, which is in data communication with the optical sensor 32, for example to trigger the electrical or electronic signals of the optical sensor 32 and / or to drive the optical sensor 32. Alternatively, the electrical or electronic signals of all pixels may be analysed to determine the magnetic field inside the sample 12, e.g. an averaged magnetic field of the sample 12.

[0255] The controller 24 includes, for example, a processor 24a and a memory 24b (an example of a computer-readable storage medium). The memory 24b may store one or more (computer) programs and / or algorithms that are executed by the processor 24a. The controller 24 can be a field-programmable gate array (FPGA) or an application-specific integrated circuit (ASIC).

[0256] The controller 24 may be in data-communication with the excitation light source 30 to control the excitation light source 30. The excitation light source 30 may include one or more lasers or other devices for generating light. The light generated by the excitation light source 30 may be in the visible wavelength range, the infrared wavelength range, or the ultraviolet wavelength range. The excitation light source 30 may be configured to selectively generate light in a selected wavelength range, for example in a wavelength range that is absorbed by the NV- centres.

[0257] The light generated by the excitation light source 30 is coupled into the wide-field microscope 14 via the beam splitter 26 and directed to the objective of the optics 28. The objective focuses the incident light onto the NV- centres in the quantum sensor device 18. The light emitted by the NV- centres is projected by the optics 28 onto the optical sensor 32. The light beams in the beam paths described here do not have to be parallel, as shown in Fig. 1.

[0258] The excitation light source 30 may continuously emit excitation light which may result in so-called CW (continuous wave) measurements. Alternatively, the excitation light generated by the excitation light source 30 may be pulsed. For example, a first pulse of excitation light is emitted prior to the generation of the microwave radiation and a second pulse of excitation light is emitted after or during the generation of the microwave radiation. In this case, the emitted fluorescent light may only be imaged during the excitation of the second pulse.Mewburn Reference: 008912990 The beam splitter 26 may be a semi-transparent mirror and / or a dichroic mirror. The choice of the type of beam splitter 26 depends on the light generated by the excitation light source 30 and which light is emitted and / or absorbed by the NV- centres.

[0259] The quantum sensor device 18 can be supported by the sample holder 16. For example, the sample holder 16 has a hole in which the quantum sensor device 18 is embedded. A surface of the sample holder 16 may form a plane with a sample side of the quantum sensor device 18. The sample 12 can be placed on the quantum sensor device 18 and / or the sample holder 16. The area where the sample 12 can be placed on the sample holder 16 and / or supported by the sample holder 16 may be regarded as a sample area.

[0260] The quantum sensor device 18 may have a cuboid shape. The NV- centres may be arranged in a layer that is located on the side of the quantum sensor device 18 that contacts the sample 12. The layer of NV- centres may have a thickness sufficiently low so that the NV- centres can be imaged or projected onto the optical sensor 32. The quantum sensor device 18 may be entirely made from diamond. The area over which the NV- centres are provided within the quantum sensor device 18 may be considered a sensor area. The sensor area may be in direct contact with the sample 12.

[0261] The sample 12 is arranged close to or in contact with the NV- centres in the quantum sensor device 18. In one example, the NV- centres of the quantum sensor device 18 are in the nearfield of the microwave radiation that is interacting with the sample 12. The near-field can be defined as a fraction of the wavelength. As the wavelength of the microwave radiation is between 1 mm and 1 m, the distance between the sample 12 and the NV- centres in the quantum sensor device 18 may be between 1 pm and 1 mm, optionally between 10 pm and 100 pm.

[0262] The microwave source 20 may include a generator (not shown in the figures) and a microwave antenna. The microwave antenna may be arranged on the side of the sample holder 16 that faces the optics 28. In other words, the microwave antenna and the optics 28 are arranged on the same side of the sample holder 16 and / or the sample area which is the area where the sample 12 can be placed on the sample holder 16. In the embodiment of Fig. 1 , the microwave antenna 20 is arranged in the space between the objective of the optics 28 and the sample holder 16.

[0263] The microwave antenna may have a ring shape or a loop shape and / or may at least partially surround the quantum sensor device 18 such that microwave radiation emitted from the antenna penetrates the quantum sensor device 18, optionally from all sides, and, optionally, is reflected back from the sample 12 to the quantum sensor device 18. In this way, the NV- centres of the quantum sensor device 18 are subjected to the microwave radiation reflected byMewburn Reference: 008912990 the sample as well as the microwave radiation directly emitted by the antenna of the microwave source 20.

[0264] The microwave source 20 can be controlled by the controller 24 and / or is in data communication with the controller 24. The microwave radiation generated by the microwave source 20 may be used to decrease and / or increase the absorption and / or emission of light by the NV- centres of the quantum sensor device 18. In an example for imaging the sample 12, the microwave radiation directly emitted by the antenna of the microwave source 20 may induce a population transfer in the excited states of the NV- centres because the energy of the microwave radiation corresponds to a gap in between two energy levels of the NV- centres. This may lead to a reduction of the emitted fluorescent light. The dips in the intensity of the fluorescent light or local extrema may correspond to the different orientations of the NV- centres relative to the microwave radiation which results in different energy levels.

[0265] The microwave radiation reflected from the sample 12 and interacting with the NV- centres of the quantum sensor device 18 may increase this population transfer, for example because the microwave radiation locally reflected an interface in the material (e.g. a conductive layer in a dielectric material) locally increases the intensity of the microwave radiation at the NV- centres. This may result in a local decrease in the intensity of the fluorescent light. This change in the intensity of the fluorescent light may be spatially resolved and / or mirrors the structure within the sample 12 that reflects the microwave radiation. This is due to the fact that the NV- centres of the quantum sensor device 18 are in the near-field of the microwave radiation that is reflected by the sample 12. In this case, sub-wavelength resolution is possible compared to the far-field. Thus, it is possible to image structures within the sample 12 that reflect the microwave radiation.

[0266] The microwave radiation may be reflected by electrical conductors within the dielectric material of the sample 12. More generally, the microwave radiation may be reflected at interfaces between two different types of material, for example at the metal-dielectric interface. In this way, it is possible to image electrical conductors within an optically non-transparent material, such as semiconductor material. The differences in the intensity of the fluorescent light emitted by the NV- centres can be displayed in image.

[0267] The scale of fluorescence measurement can be corrected by a baseline at which no or little microwave radiation is reflected back. This may correspond to the dip or decrease in the microwave radiation.

[0268] Alternatively, the microwave source 20 can be used to emit microwave pulses for Rabi measurements, Ramsey measurements, CW-ODMR, pulsed ODMR, Hahn echo measurements, and / or dynamical decoupling for AC magnetometry.Mewburn Reference: 008912990 The magnetic source 22 may include a permanent magnet that generates a constant and / or homogeneous device magnetic field within the sensor area. The permanent magnet may induce a Zeeman split in the energy levels of the NV- centres.

[0269] In an alternative embodiment, the magnetic source 22 may alternatively or additionally include a generator (not shown in figures) and a coil for generating the device magnetic field. Again, the device magnetic field may be constant and / or homogeneous, for example within the sample 12 and / or the sensor area. The controller 24 may be configured to vary the orientation and / or the strength of the device magnetic field between measurements. This means that, for a particular measurement, the device magnetic field is constant and may be changed for the next measurement. A measurement may be considered as imaging the fluorescent light emitted by the NV- centres. The magnetic source 22 may generate the device magnetic field for generating a magnetic response by the sample 12 that is measured using the quantum sensor device 18.

[0270] A method for determining a quality of a sample which includes a method of imaging and / or measuring a physical property of the sample 12, such as an electromagnetic field from the sample 12, is described in connection with the block diagram of Fig. 2.

[0271] In step S1 , the sample 12, which can be an integrated circuit, is placed in contact to or adjacent to the sensor area of the quantum sensor device 18. This may include laying the sample 12 on the sample holder 16, optionally on the quantum sensor device 18. Step S1 may further include fixing the sample 12 to the sample holder 16, for example using a removable fastening means. In this way, the quantum sensor device 18 is arranged adjacent to the sample 12 such that the colour centres (e.g. the NV- centres) inside the quantum sensor device 18 are subjected to electromagnetic field from the sample 12. In this way, the intensity of the fluorescent light emitted by the colour centres changes in accordance with changes in the electromagnetic field from the sample 12.

[0272] In step S2, the device magnetic field is generated by the magnetic source 22. The device magnetic field may be continuously generated over the next steps S3 to S6. The device magnetic field may be generated for inducing a Zeemann-split in the energy levels of the NV- centres. The device magnetic field splits an energy level of the colour centres in at least a first energy level and a second energy level, each energy level may show three Hyperfine states. In this example, the device magnetic field has a first configuration which describes the orientation and / or the strength of the device magnetic field.

[0273] In step S3, excitation light is emitted by the excitation light source 30 and directed onto the colour centres in the quantum sensor device 18 using the optics 28, for example using the beam splitter 26 and the objective of the optics 28. The excitation light may be continuouslyMewburn Reference: 008912990 emitted. Alternatively, one or more pulses of the excitation light are generated for exciting the colour centres.

[0274] In step S4, microwave radiation is emitted by the microwave source 20. The microwave source 20 simultaneously generates microwave radiation of at least two frequencies (e.g. a first frequency and a second frequency) and modulates the amplitude of the microwave radiation having the first frequency and of the microwave radiation having the second frequency. The first frequency is within a first frequency range and the second first frequency is within the first frequency range or a second frequency range. The first frequency range covers a value of the frequency in which the generated microwave radiation is in resonance with the colour centres wherein the microwave radiation resonates with the first energy level induced by the device magnetic field generated in step S2. The second frequency range covers a value of the frequency in which the generated microwave radiation is in resonance with the colour centres wherein the microwave radiation resonates with the second energy level induced by the device magnetic field generated in step S2.The first value of the first frequency and / or the second frequency may correspond to microwave radiation that is off resonance with the first energy level of the colour centres such that the received fluorescent light corresponds to a base level.

[0275] The microwave radiation may be simultaneously emitted with the emission of the excitation light as for example used with cw-ODMR measurements. Alternatively, a pulse of the microwave radiation is emitted after the pulse of the excitation light. In this case, a further pulse of the excitation light can be emitted during or after the pulse of the microwave radiation as for example used with pulsed ODMR measurements.

[0276] In step S5, the fluorescent light emitted by the colour centres is recorded. To this end, the fluorescent light emitted by the colour centres is projected onto the optical sensor 32. The optical sensor 32 converts the received fluorescent light into electronic signals wherein the value of the electronic signals corresponds to the intensity and / or the wavelength of the received resonance light. This process is made for each pixel of the colour centres 32. For example, if the optical sensor 32 includes 1032x1032 pixels, 1032x1032 electronic signals are generated. Each electronic signal may correspond to the fluorescent light emitted by the colour centres located in the area corresponding to each pixel on the optical sensor 32.

[0277] Steps S3 and S5 are repeated for various values of the modulated amplitude of the microwave radiation having the first frequency and the second frequency. For example, the amplitude is held constant during the time the electronic signals are recorded. Thereafter, the amplitude is increased or decreased by a certain amount and the changed amplitude is held constant during the time the electronic signals are recorded. This is repeated several times (e.g. 50 or 100 times) to record the temporal behaviour of the electronic signals with regard to the modulated amplitude. In other words, it is possible to extract from the time series of the electronic signals aMewburn Reference: 008912990 change in the values of the electronic signals which corresponds to the amplitude modulation of the microwave radiation having the first frequency and the microwave radiation having the second frequency.

[0278] Fig. 6 shows two examples of a stepwise modulation of the amplitude of six frequencies that are simultaneously generated. Each measurement is depicted by the six horizontal lines wherein each horizontal line depicts the amplitude of the microwave radiation having a respective frequency for a particular time period during which the electronic signals are recorded. The ratio between a modulation frequency (a frequency of the modulation of the amplitude) to the respective frequency of the microwave radiation can be a prime number for reducing crosstalk between the different frequencies. This is apparent from Fig. 6 in that, for each recording of the electronic signals, the amplitudes of the respective frequency are set to different levels. For example, a change in the amplitude of the first frequency is different to a change of the amplitude of the second frequency between different time periods for recording the electronic signals.

[0279] In step S6, steps S3 to S5 are repeated many times whereby, each time, the frequency of the microwave radiation has a value different to the value of the frequency that is used in any other repetition of steps S3 to step S5. In other words, each frequency of the microwave radiation is changed with each repetition. In this way, the intensity of the fluorescent light is recorded for all selected values of the frequency in the first frequency range and / or in the second frequency range. This applies to both the first frequency and the second frequency.

[0280] Prior to step S6, the sampling frequency of the first frequency range and / or the second frequency range can be set. This corresponds to the number of repetitions that are made in step S6. Optionally, the chosen values of the frequency in the first frequency range and / or the second frequency range as well as the breadth of the first frequency range and / or the second frequency range are chosen to detect extrema in the electronic signals.

[0281] The first frequency range and / or the second frequency range may be located around the first energy level and the second energy level such that extrema induced by the first energy level and the second energy level can be recorded in step S6.

[0282] As an example of step S6, the frequency of the microwave radiation is swept in the first frequency range and, simultaneously, in the second frequency range because the first frequency and the second frequency are simultaneously generated. As apparent from Fig. 5, six frequencies are swept across the various extrema in the intensity of the emitted fluorescent light or, in other words, over various resonances of the colour centres. In this example, the device magnetic field is held constant. Please note that Figs. 4 and 5 do not show the recorded electronic signals. Rather, the curves show lines corresponding to extracted data points whichMewburn Reference: 008912990 indicate the fluorescence response of the colour centres for each frequency. The extraction step of the data points from the electronic signals is described in the step S8. Fig. 5 shows the lines for six frequencies that are simultaneously generated and recorded.

[0283] In optional step S7, reference recordings are taken between the time periods for recording the electronic signals. This is shown in the upper diagram of Fig. 6. During the reference recordings, no microwave is generated and the fluorescence response of the colour centres is recorded, i.e. the colour centres are not manipulated or excited by the microwave radiation. As apparent from Fig. 6, the reference recordings can be taken between each time period for recording the electronic signals.

[0284] The electronic signals recorded for a particular value of the amplitude modulation are referenced to a previous or subsequent reference recording. For example, the electronic signals recorded for a particular value of amplitude modulation are divided by the electronic signals recorded during the reference recording. This may reduce or eliminate noise such as laser noise from the electronic signals. This process is repeated for each pixel and each pair of reference recording and recording of the electronic signals during a particular value of the amplitude modulation.

[0285] Alternatively, as shown in the lower diagram of Fig. 6, the reference recordings may be omitted in optional step 7. Optionally, the electronic signals recorded for a particular value of the amplitude modulation are referenced to the electronic signals recorded for previous or subsequent value of the amplitude modulation. In this case, the reference measurements can be omitted which reduces (halves) the time required for a measurement is readily apparent from Fig. 6.

[0286] For referencing subsequently recorded electronic signals, the value of the electronic signal for a particular pixel can be divided by the value of the electronic signal for the same pixel for the recording of the electronic signals with a different value of the amplitude modulation. For example, this may be done by calculating a reference ratio, which is the electronic signal recorded for a particular value of the amplitude modulation is divided by the electronic signal recorded for previous or subsequent value of the amplitude modulation.

[0287] In step S8, data points corresponding to the fluorescence response of the colour centres as excited by the first frequency and data points corresponding to the fluorescence response of the colour centres as excited by the second frequency are extracted from the recorded electronic signals of Step S6 or from the referenced recorded electronic signals of step S7. The extraction of the data points may include Fourier transforming the (referenced) electronic signals or the reference ratios for each pixel, for example using a fast Fourier transformation a lock-in discreteMewburn Reference: 008912990 Fourier transformation (DFT) since the phase is known with which the system is driven. As the amplitudes of the first frequency and the second frequency were modulated with different frequencies, the Fourier transformation of the electronic signals include information on the fluorescence response of the colour centres as excited by the first frequency and the second frequency. In this way, after multiplexing the first and second frequencies into the microwave radiation emitted to the colour centres, the information can be deplexed from the electronic signals. In this way it is possible to generate two sets of data points from a single set of electronic signals. In other words, the extracted data points show the frequency-dependent fluorescence response of the colour centres for two different frequencies that would have been generated with known instruments by two subsequent measurements. In this way, the measurement time can be halved and, if six frequencies are simultaneously generated, six series of data points can be generated reducing the measurement time to a sixth of the measurement time required for known instruments.

[0288] In step S9, the electromagnetic field of the sample 12 is calculated for each pixel based on the data points extracted in step S8. For example, curves can be fitted to the data points for the first frequency range and the second frequency range. Extrema in the curves can be determined. Changes in the position and / or the amplitude of the extrema between the first and second frequency ranges can be used to calculate the electromagnetic field of the sample 12.

[0289] Alternatively, the extracted data points for the first frequency range and the second frequency range are cross-correlated - for each pixel. Optionally, the cross-correlation is calculated using a discrete Fast-Fourier transformation as known in the prior art. Then, an extremum of the cross-correlation is determined. This may be done by fitting a curve to the cross-correlation and determining the extremum of the curve. The position of the extremum corresponds to a shift of the parameter, such as a frequency lag, between the first frequency range and the second frequency range (e.g. between extrema in the first frequency range and the second frequency range). This shift of the frequency may be used to calculate the electromagnetic field. For example, the calculated frequency shift may be proportional to the electromagnetic field from the sample 12. This process is done for each pixel such that an image of the electromagnetic field (such as a vector field of the sample 12) can be generated. The image may show the variation of the intensity and / or orientation of the electromagnetic field over the many pixels.

[0290] Step S9 or steps S1 to S9 can be executed in real-time. For example, the total time for executing step S9 or steps S1 to S9 can be less than 0.1 s, 1 s, or 10 s. Steps S1 to S9 may be considered corresponding to the method of imaging and / or measuring an electromagnetic field from the sample 12.

[0291] In Step S10, a quality of the sample 12 is determined based on the calculated electromagnetic field of the sample as done in step S9. The quality of the sample 12 may be determined byMewburn Reference: 008912990 generating one or more quality parameters of the sample 12. For example, the quality parameter refers to a value indicating the strength and / or orientation of the electromagnetic field. A quality parameter can be generated for different locations of the sample 12, e.g. for each pixel or zone of interest. The generated quality parameter can be compared with a predetermined parameter range. If one, more, or all quality parameters are within their respective parameter ranges, the sample 12 fulfils the quality assessment. For example, if the sample 12 is a manufactured semiconductor circuit, this may indicate that the semiconductor circuit was correctly manufactured. Alternatively, if the sample is a cell, fulfilling the quality may indicate that the cell is a cancerous cell or a certain type of cell.

[0292] Step S10 optionally includes generating a rejection signal and / or a feedback signal. The rejection signal and / or the feedback signal may be generated if the sample 12 does not fulfil the desired quality, e.g. if one, more, or all quality parameters are outside their respective parameter ranges. The rejection signal may be used for removing the semiconductor circuit from the manufacturing line. The feedback signal may be used for adjusting or changing the manufacturing process.

[0293] A computer-implemented method of imaging and / or measuring an electromagnetic field from the sample 12 and for determining a quality parameter of the sample 12 is described in connection with the block the diagram of Fig. 3. The method may be executed on the controller 24. The algorithm or computer program comprises instructions which, when the algorithm or computer program is executed by the controller 24, causes the controller 24 to carry out the steps of this method. The algorithm or computer program may be stored on the memory 24b of the controller 24 or on an external computer-readable storage medium in data-communication with the controller 24.

[0294] In optional step S11 , the controller 24 may request confirmation by the user that the sample 12 is placed in contact to or adjacent to the sensor area of the quantum sensor device 18. The user may place the sample 12 as described in connection with above step S1.

[0295] In optional step S12, the controller 24 may generate control signals to be sent to the magnetic source 22 (e.g. instructions in a data format readable by the magnetic source 22). The control signals prompt the magnetic source 22 to start generating the device magnetic field. The device magnetic field may be continuously generated over the next steps S12 to S15. As described in connection with step S2, the device magnetic field may be generated for inducing a Zeemann-split in the energy levels of the colour centres.

[0296] In step S13, the controller 24 may generate control signals to be sent to the excitation light source 30 (e.g. instructions in a data format readable by the excitation light source 30). The control signals prompt the excitation light source 30 to start generating the excitation lightMewburn Reference: 008912990 directed onto the colour centres in the quantum sensor device 18. As described in connection with step S3, the control signals of step S13 may include point of time and / or the duration of the excitation light to be generated.

[0297] In step S14, the controller 24 may generate control signals to be sent to the microwave source 20 (e.g. instructions in a data format readable by the microwave source 20). The control signals prompt the microwave source 20 to start generating microwave radiation. The control signals may specify the value of the first and second frequencies (or any additional frequency) as described in connection with above step S4.

[0298] In step S15, the controller 24 receives the electronic signals from the optical sensor 32. As described in connection with step S5, the electronic signals are indicative of the fluorescent light emitted by the colour centres.

[0299] In step S16, the controller 24 records the electronic signals received in step S15. This step may include storing the electronic signals received in step S15 on the memory 24b of the controller 24.

[0300] In step S17, steps S13 to S16 are repeated many times whereby, each time, the control signals to be sent to the microwave source 20 is varied in the value of the amplitude and the frequency as described in connection with steps S3 to S6.

[0301] In step S18, the controller 24 extracts the data points from the electronic signals recorded in the previous steps as described in connection with step S8. Alternatively, the controller 24 references the electronic signals as described in step S7 and extracts the data points from the referenced electronic signals or the reference ratios as described in step S8.

[0302] In step S19, the controller 24 determines changes in the extracted data points as extracted in step S17. This may include cross-correlating - for each pixel - the extracted data points in the first frequency range with the extracted data points in the second frequency range. Optionally, the cross-correlation is calculated using a discrete Fast-Fourier transformation as known in the prior art. These steps may be similar or identical to the step S8 described above.

[0303] In step S20, the controller 24 calculates the electromagnetic field of the sample 12 for each pixel based on cross-correlation obtained in step S19. This may be done similar or identical to step S9 described above.

[0304] In step S21 , the controller 24 determines a quality parameter of the sample 12. This may be done similar or identical to step S10 described above.Mewburn Reference: 008912990 An alternative to steps S4 to S6 includes generating microwave radiation having a first frequency set and a second frequency set. The first frequency set includes the first frequency and two or more frequencies in the first frequency range. The difference between the frequencies of the first frequency set is not varied over the various measurements and may correspond to a frequency difference between two energy levels in the first frequency range. For example, the first frequency set includes three frequencies whose difference corresponds to the frequency difference of the triplet of NV centres (corresponding to three individual Hyperfine states of the NV centres). Similarly, the second frequency set includes the second frequency and two or more frequencies in the second frequency range. The difference between the frequencies of the second frequency set is not varied over the various measurements and may correspond to a frequency difference between two energy levels in the first frequency range. For example, the second frequency set includes three frequencies whose difference corresponds to the frequency difference of another triplet of NV centres (corresponding to another three individual Hyperfine states of the NV centres).

[0305] If the first and second frequency sets are swept over the respective triplet, the received electronic signals exhibit a convolution of the frequency set with the triplet as shown in Fig. 4. Thereby, five extrema are generated. As the individual frequencies of the first or second frequency sets are chosen with respect to the respective triplets, the amplitude of the middle extremum is (three times) greater than the amplitude of the two outer extrema (which would correspond the amplitude of the electronic signal if a single frequency was swept over the triplet). In this way, the contrast of the electronic signals and, therefore, the calculation of the electromagnetic field can be improved.

[0306] The electronic signals from the first and / or second frequency sets need not to be amplitude-modulated when the first frequency set and the second frequency set are measured after another because it is possible to deconvolute the electronic signals. However, similar to step S4, the first frequency set and second frequency set are simultaneously generated whereby the frequencies of the first frequency set are modulated by the same first modulation frequency and the frequencies of the second frequency set are modulated by the same second modulation frequency different to the first modulation frequency. Thereafter, the first frequency set and the second frequency set can be swept over the first frequency range and the second frequency range, respectively, as described above.

[0307] After the data points corresponding to the first frequency set and the second frequency set have been extracted from the recorded electronic signals, the electromagnetic field can be generated. Fig. 5 shows curves of the extracted data points corresponding to six frequencies of the first frequency set.Mewburn Reference: 008912990 In a further alternative, a plurality of frequencies is simultaneously generated and modulated in step S4. The number of frequencies may be chosen to provide a good distribution over the first frequency range and / or the second frequency range such that the electromagnetic field can be calculated from the extracted data points. In this alternative, the frequencies are not swept. Rather, the high number of simultaneously generated frequencies allows sampling the first and / or second frequency ranges.

[0308] While this invention has been particularly shown and described with reference to embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the scope of the invention as defined by the appended claims.

Claims

Mewburn Reference: 008912990CLAIMS:1 . A quantum device for imaging and / or measuring a physical property, comprisinga quantum sensor device (18) including colour centres in a sensor area, the quantum sensor device (18) being configured to be subjected to the physical property, the colour centres being configured to emit fluorescence light depending on the physical property,an excitation light source (30) configured to generate excitation light directed to the quantum sensor device (18) for exciting the colour centres to emit the fluorescence light, an optical sensor (32) including one or more pixels and configured to generate electronic signals indicative of an intensity of the light emitted by the colour centres,optics (28) configured to project the colour centres onto the optical sensor (32), a microwave source (20) including a microwave antenna for emitting microwave radiation towards the sensor area, the microwave source (20) being configured to generate microwave radiation including at least two different frequencies and to modulate an amplitude of the generated microwave radiation,a magnetic source (22) for generating a device magnetic field in the sensor area, the device magnetic field inducing a split of an energy level of the colour centres into at least a first energy level and a second energy level, anda controller (24) in data-communication with the microwave source (20) and the optical sensor (32),wherein the controller (24) is configured to(i) control the microwave source (20) to simultaneously generate a microwave radiation having a first frequency and a microwave radiation having a second frequency, the first frequency being in a first frequency range in which the first energy level resonates with the microwave radiation, and the second frequency being in the first frequency range or a second frequency range in which the second energy level resonates with the microwave radiation, (ii) control the microwave source (20) to modulate - using one or more modulation frequencies - the amplitudes of the microwave radiation having the first frequency and the microwave radiation having the second frequency,(iii) record - for each pixel - the electronic signals received from the optical sensor (32) for the modulated amplitudes of the microwave radiation having the first frequency and / or the microwave radiation having the second frequency,(iv) extract - for each pixel and using the one or more modulation frequencies -data corresponding to the first frequency and the second frequency from the electronic signals, and(v) calculate the physical property using the extracted data corresponding to the first frequency and the second frequency.Mewburn Reference: 008912990 2. The quantum device of claim 1 , wherein the controller is configured to control the microwave source (20) to modulate the microwave radiation having the first frequency with a first modulation frequency and to modulate the microwave radiation having the second frequency with a second modulation frequency which is different to the first modulation frequency.

3. The quantum device of claim 2, wherein a first modulation ratio of the first modulation frequency to the first frequency is a prime number and / or a second modulation ratio of the second modulation frequency to the second frequency is a prime number.

4. The quantum device of claim 2 or 3, wherein the controller (24) is configured to control the microwave source (20) to modulate the microwave radiation such that the amplitudes of the microwave radiation having the first frequency and the microwave radiation having the second frequency remain constant during the recording of the electronic signals and are changed between recording of the electronic signals.

5. The quantum device of any preceding claim, wherein the controller (24) is configured to vary the first frequency and the second frequency for sweeping the first frequency in the first frequency range and the second frequency in the first frequency range or the second frequency range,wherein the controller (24) is further configured repeat items (i) to (iv) for each varied first frequency and second frequency,wherein - with item (v) - the controller (24) is configured todetermine an extremum in the extracted data corresponding to the first frequencies and an extremum in the extracted data corresponding to the second frequencies, andcalculate the physical property using the extrema.

6. The quantum device of any preceding claim, wherein the controller (24) is configured to simultaneously generate a plurality of first frequencies in the first frequency range and a plurality of second frequencies in the first frequency range and / or the second frequency range, wherein - with item (iv) - the controller (24) is configured to extract - for each pixel and using the modulation frequencies - data corresponding to each one of the first frequencies and to each one of the second frequencies from the electronic signals, andwherein - with item (v) - the controller (24) is configured todetermine an extremum in the extracted data corresponding to the plurality of the first frequencies and an extremum in the extracted data corresponding to the plurality of the second frequencies, andcalculate the physical property using the extrema.

7. The quantum device of any preceding claim, wherein the controller (24) is configured toMewburn Reference: 008912990 (I) control the microwave source (20) to simultaneously generate a microwave radiation having a first frequency set and a microwave radiation having a second frequency set, the first frequency set being in the first frequency range and including the first frequency and one or more additional first frequencies, and the second frequency set being in the first frequency range or the second frequency range and including the second frequency and one or more additional second frequencies,(II) control the microwave source (20) to modulate - using the one or more modulation frequencies - the amplitudes of the microwave radiation having the first frequency set and the microwave radiation having the second frequency set,(III) record - for each pixel - the electronic signals received from the optical sensor (32) for the modulated amplitudes of the microwave radiation having the first frequency set and the microwave radiation having the second frequency set,(IV) extract - for each pixel and using the one or more modulation frequencies -data corresponding to the first frequency set and the second frequency set from the electronic signals, and(V) calculate the physical property using the extracted data corresponding to the first frequency set and the second frequency set.

8. The quantum device of claim 7, wherein the controller (24) is configured to vary the first frequency set and the second frequency set for sweeping the first frequency set in the first frequency range and the second frequency set in the first frequency range or the second frequency range,wherein the controller (24) is further configured repeat items (I) to (IV) for each varied first frequency set and second frequency set,wherein - with item (V) - the controller (24) is configured todetermine an extremum in the extracted data corresponding to the first frequencies and an extremum in the extracted data corresponding to the second frequencies, andcalculate the physical property using the extrema.

9. The quantum device of any preceding claim, wherein, for providing a reference of the noise of the excitation light source (30), the controller (24) is configured to control the microwave source (20) not to emit microwave radiation and to record - for each pixel - reference electronic signals received from the optical sensor (32),wherein the controller (24) is configured to - for each pixel - calculate a ratio of the recorded electronic signals and the reference electronic signals, andwherein - with item (iv) - the controller (24) is configured to extract - for each pixel and using the one or more modulation frequencies - data corresponding to the first frequency and the second frequency using the calculated ratio.Mewburn Reference: 008912990 10. The quantum device of any one of the claims 5 to 9, wherein, for providing a reference of the noise of the excitation light source (30), the controller (24) is configured to - for each pixel -calculate a reference ratio of the electronic signal corresponding to the microwave radiation having the first frequency and the second frequency and the electronic signal corresponding to microwave radiation having the varied first frequency and the varied second frequency and / or a varied amplitude, andwherein - with item (iv) - the controller (24) is configured to extract - for each pixel and using the one or more modulation frequencies - data corresponding to the first frequency and the second frequency using the reference ratio.

11. The quantum device of any preceding claim, wherein the quantum sensor device (18) includes a diamond having negatively charged nitrogen vacancy (NV ) centres as colour centres and the first energy level and the second energy level correspond to a Zeeman shift induced by the device magnetic field.

12. A method for imaging and / or measuring a physical property, comprising the steps of arranging a quantum sensor device (18) including colour centres in a sensor area to be subjected to the physical property, the colour centres being configured to emit fluorescence light depending on the electromagnetic field,generating, by an excitation light source (30), excitation light directed to the quantum sensor device (18) for exciting the colour centres to emit the fluorescence light, projecting, by optics (28), the colour centres onto the optical sensor (32), generating, by a magnetic source (22), a device magnetic field in the sensor area, the device magnetic field inducing a split of an energy level of the colour centres into at least a first energy level and a second energy level,controlling a microwave source (20) for simultaneously generating a microwave radiation having a first frequency and a microwave radiation having a second frequency, the first frequency being in a first frequency range in which the first energy level resonates with the microwave radiation, and the second frequency being in the first frequency range or a second frequency range in which the second energy level resonates with the microwave radiation, modulating - using one or more modulation frequencies - the amplitudes of the microwave radiation having the first frequency and the microwave radiation having the second frequency,recording - for each pixel of the optical sensor (32) - the electronic signals received from the optical sensor (32) for the modulated amplitudes of the microwave radiation having the first frequency and / or the microwave radiation having the second frequency,extracting - for each pixel and using the one or more modulation frequencies - data corresponding to the first frequency and the second frequency from the electronic signals, and calculating the physical property using the extracted data corresponding to the first frequency and the second frequency.Mewburn Reference: 00891299013. A method for determining a quality of a sample (12), comprising the steps of imaging and / or measuring a physical property of the sample (12) using the method of claim 12 in real-time,determining the quality of the sample (12) based on the imaged and / or measured physical property of the sample (12).

14. The method of claim 13, further comprising rejecting the sample (12) if the sample (12) does not conform to the determined quality and / or generating a feedback signal based on the determined quality for changing the manufacturing process of the sample (12).

15. A controller for a quantum device for imaging and / or measuring a physical property, the quantum device (10) comprisinga quantum sensor device (18) including colour centres in a sensor area, the quantum sensor device (18) being configured to be subjected to the physical property, the colour centres being configured to emit fluorescence light depending on the electromagnetic field, and a magnetic source (22) for generating a device magnetic field in the sensor area, the device magnetic field inducing a split of an energy level of the colour centres into at least a first energy level and a second energy level,wherein the controller (24) comprisesa first output port configured to be connected to an excitation light source (30), the excitation light source (30) configured to generate excitation light directed to the quantum sensor device (18) for exciting the colour centres to emit the fluorescence light,a second output port configured to be connected to a microwave source (20) including a microwave antenna for emitting microwave radiation towards the sensor area, the microwave source (20) being configured to generate microwave radiation including at least two different frequencies and to modulate an amplitude of the generated microwave radiation, and an input port configured to be connected to an optical sensor (32) including one or more pixels, the optical sensor (32) being configured to generate electronic signals indicative of an intensity of the light emitted by the colour centres, andwherein the controller (24) is configured to(i) control the microwave source (20) to simultaneously generate a microwave radiation having a first frequency and a microwave radiation having a second frequency, the first frequency being in a first frequency range in which the first energy level resonates with the microwave radiation, and the second frequency being in the first frequency range or a second frequency range in which the second energy level resonates with the microwave radiation, (ii) control the microwave source (20) to modulate - using one or more modulation frequencies - the amplitudes of the microwave radiation having the first frequency and the microwave radiation having the second frequency,Mewburn Reference: 008912990 (iii) record - for each pixel - the electronic signals received from the optical sensor (32) for the modulated amplitudes of the microwave radiation having the first frequency and / or the microwave radiation having the second frequency,(iv) extract - for each pixel and using the one or more modulation frequencies -data corresponding to the first frequency and the second frequency from the electronic signals, and(v) calculate the physical property using the extracted data corresponding to the first frequency and the second frequency.

16. The controller of claim 15, wherein the controller (24) is a field-programmable gate array (FPGA) or an application-specific integrated circuit (ASIC).

17. A computer-implemented method for imaging and / or measuring a physical property, the quantum device (10) comprisinga quantum sensor device (18) including colour centres in a sensor area, the quantum sensor device (18) being configured to subjected to the physical property, the colour centres being configured to emit fluorescence light depending on the physical property, and a magnetic source (22) for generating a device magnetic field in the sensor area, the device magnetic field inducing a split of an energy level of the colour centres into at least a first energy level and a second energy level,wherein the method comprises the steps ofgenerating control signals to be sent to an excitation light source (30) such that the excitation light source (30) generates excitation light directed to the quantum sensor device (18) for exciting the colour centres to emit the fluorescence light,generating control signals to be sent to a microwave source (20) for simultaneously generating microwave radiation having a first frequency and a microwave radiation having a second frequency, the first frequency being in a first frequency range in which the first energy level resonates with the microwave radiation, and the second frequency being in the first frequency range or a second frequency range in which the second energy level resonates with the microwave radiation,receiving electronic signals indicative of an intensity of the light emitted by the colour centres from an optical sensor (32) including a one or more pixels,recording - for each pixel - the electronic signals received from the optical sensor (32) for the modulated amplitudes of the microwave radiation having the first frequency and / or the microwave radiation having the second frequency,extracting - for each pixel and using the one or more modulation frequencies -data corresponding to the first frequency and the second frequency from the electronic signals, andcalculating the physical property using the extracted data corresponding to the first frequency and the second frequency.Mewburn Reference: 00891299018. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the steps of the method of claim 17.

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