Quantum device and methods for imaging or measuring an electromagnetic field from a sample

Abstract

The invention refers to a quantum device for imaging and / or measuring an electromagnetic field from a sample (12), wherein a controller (24) is configured to control the microwave source (20) for varying at least one parameter of the plurality of parameters in a first parameter range in which the first energy level resonates with the microwave radiation and a second parameter range in which the second energy level resonates with the microwave radiation, record - for each pixel - the electronic signals received from the optical sensor (32) for a plurality of variations of the parameter in the first parameter range and the second parameter range, determine - for each pixel - changes in the electronic signals by cross-correlating the electronic signals generated over first parameter range with the electronic signals generated over second parameter range, and calculate the electromagnetic field of the sample (12) based on the cross-correlation.

Description

[0001] 008866436

[0002] Quantum Device and Methods for Imaging or Measuring an Electromagnetic Field from a Sample

[0003] FIELD OF THE INVENTION

[0004] The invention relates to a quantum device for imaging and / or measuring an electromagnetic field from a sample. The quantum sensor device comprises a quantum sensor device, an excitation light source, an optical sensor, and imaging optics. The quantum sensor device includes colour centres in a sensor area. The quantum sensor device is configured to be arranged adjacent to the sample to be subjected to the electromagnetic field. 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 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 imaging optics are configured to project the colour centres onto the optical sensor.

[0005] The invention further relates to a method for imaging and / or measuring an electromagnetic field from 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 electromagnetic field, the being configured to emit fluorescent light depending on the electromagnetic field, (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, and (c) projecting, by imaging optics, the colour centres onto the optical sensor.

[0006] Furthermore, the invention relates to a method for determining a quality of a sample.

[0007] The invention also refers to a controller for a quantum device for imaging and / or measuring an electromagnetic field from a sample, for example as used with the quantum device.

[0008] The invention relates to a computer-implemented method for imaging and / or measuring an electromagnetic field from a sample, a computer program, and a computer-readable storage medium.

[0009] BACKGROUND

[0010] Point defects in synthetic diamond material, particularly quantum spin defects and / or optically active defects, have been proposed for use in various 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. 008866436

[0011] 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 as 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.

[0012] 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:

[0013] 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);

[0014] 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. 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. 008866436

[0017] SUMMARY

[0018] An object of the invention is to provide a quantum device, a controller, and method for providing improved imaging and / or measuring of an electromagnetic field from a sample.

[0019] At its most general, the invention refers to optically exciting the colour centres and measuring the fluorescent light emitted by the colour centres. For imaging and / or measuring an electromagnetic field from a sample, the colour centres are subjected to microwave radiation having a parameter which changes the fluorescence of the colour centres. The fluorescence response of the colour centres is detected at two energy transitions or levels of the colour centres. The respective fluorescence responses at the two energy levels are cross correlated for detecting variations in the respective fluorescence responses. The cross-correlation is used to determine the electromagnetic field from the sample. For example, a change in the crosscorrelation may be indicative of a change in the electromagnetic field from the sample.

[0020] According to a first aspect, there is provided a quantum device for imaging and / or measuring an electromagnetic field from a sample. The quantum sensor device comprises a quantum sensor device, an excitation light source, an optical sensor, imaging optics, 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 arranged adjacent to the sample to be subjected to the electromagnetic field. The colour centres are configured to emit fluorescent light depending on the electromagnetic field. 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 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 imaging optics are configured to project the colour centres onto the optical sensor. The microwave source includes a microwave antenna for emitting microwave radiation towards the sensor area. The microwave radiation can be characterized by a plurality of parameters. 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 and the optical sensor. The controller is configured to (i) control the microwave source for varying at least one parameter of the plurality of parameters in a first parameter range in which the first energy level, optionally a transition to or from the first energy level, resonates with the microwave radiation and a second parameter range in which the second energy level, optionally a transition to or from the second energy level, resonates with the microwave radiation, (ii) record - for each pixel - the electronic signals received from the optical sensor for a plurality of variations of the parameter in the first parameter range and the second parameter range, (iii) determine - for each pixel - changes in the electronic signals by cross-correlating the electronic signals generated over first parameter range with the electronic 008866436 signals generated over second parameter range, and (iv) calculate the electromagnetic field of the sample based on the cross-correlation.

[0021] According to a second aspect, there is provided a method for imaging and / or measuring an electromagnetic field from 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 electromagnetic field, the colour centres being configured to emit parameter frequency of a microwave radiation to be emitted towards the sensor area over a first parameter range in which the first energy level, optionally a transition to or from the first energy level, resonates with the microwave radiation and a second parameter range in which the second energy level, optionally a transition to or from the second energy level, resonates with the microwave radiation, the microwave radiation being characterized by a plurality of parameters, (f) recording - for each pixel of an optical sensor - electronic signals for a plurality of variations of the parameter in the first parameter range and the second parameter range, the electronic signals being indicative of an intensity of the light emitted by the colour centres, (g) determining - for each pixel - changes in the electronic signals by cross-correlating fluorescent light depending on the electromagnetic field, (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, (c) projecting, by imaging optics, the colour centres onto the optical sensor, (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 varying at least one the electronic signals generated over first parameter range with the electronic signals generated over second parameter range, and / or (h) calculating the electromagnetic field of the sample based on cross-correlation.

[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, 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 an electromagnetic field from 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 arranged adjacent to the sample to be subjected to the electromagnetic field. The colour centres are configured to emit fluorescent light depending on the electromagnetic field. 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, a second output port, and / or an input port. The first output port is 008866436 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 excitation light source for exciting the colour centres, (ii) control the microwave source for varying a parameter of the microwave radiation over a first parameter range in which the first energy level, optionally a transition to or from the first energy level, resonates with the microwave radiation and a second parameter range in which the second energy level, optionally a transition to or from the second energy level, resonates with the microwave radiation, the microwave radiation being characterized by a plurality of parameters, (iii) record - for each pixel - the electronic signals received from the optical sensor for a plurality of variations of the parameter in the first parameter range and the second parameter range, (iv) determine - for each pixel - changes in the electronic signals by cross-correlating the electronic signals generated over first parameter range with the electronic signals generated over second parameter range, and (v) calculate the electromagnetic field of the sample based on the crosscorrelation.

[0024] According to a fourth aspect, there is provided a computer-implemented method for imaging and / or measuring an electromagnetic field from 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 arranged adjacent to the sample to be subjected to the electromagnetic field. The colour centres are configured to emit fluorescent light depending on the electromagnetic field. 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, (B) generating control signals to be sent to a microwave source for varying a parameter of the microwave radiation emitted by the microwave source over a first parameter range in which the first energy level, optionally a transition to or from the first energy level, optically excitable and a second parameter range in which the second energy level, optionally a transition to or from the second energy level, is optically excitable, the microwave radiation being characterized by a plurality of parameters, (C) receiving electronic signals indicative of an intensity of the light emitted by the colour centres from an optical sensor including one or more pixels, (D) recording - for each pixel - the electronic signals received from the optical sensor for a plurality of variations of the parameter in 008866436 the first parameter range and the second parameter range, (D) determining - for each pixel - changes in the electronic signals by cross-correlating the electronic signals generated over first parameter range with the electronic signals generated over second parameter range, and (E) calculating the magnetic field of the sample based on the cross-correlation.

[0025] Steps (A) to (E) 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, and / or one or more steps are repeated twice or more for the method described herein.

[0026] 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.

[0027] 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.

[0028] 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 an electromagnetic field 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 electromagnetic field of the sample, optionally in real-time.

[0029] The devices and methods described herein are based on the discovery of the inventors that the recorded fluorescence of the colour centres has the same shape or form over the varied parameter of the microwave radiation in both energy levels for each pixel. The same shape or form can be used for detecting changes between the respective energy levels using the crosscorrelation. The shape or form of the recorded fluorescence over the varied parameter of the microwave radiation at a different location of the quantum sensor device (which may correspond to a different pixel) can vary significantly. In this case, a cross-correlation may not achieve the desired results. However, comparison of different energy levels using a cross-correlation is possible due to the almost identical shape or form of the recorded fluorescence over the varied parameter. Using a cross-correlation reduces the required time for calculating changes in the detected fluorescence response. The changes in the fluorescence response can be used to determine the electromagnetic field from the sample.

[0030] Further, with known techniques, peaks or dips in the detected fluorescence response of the samples are calculated by fitting a curve to the detected fluorescence response varied over the parameter of the microwave radiation. This often requires making assumptions on the shape or 008866436 form of the curve. If however the detected curve deviates from the assumed shape form of the curve, this technique may produce errors. For example, a parametric model shape is set in advance with respect to the expected shape of the intensity of the fluorescent light over the varied parameter. However, if the actual / recorded intensity of the fluorescent light over the varied parameter varies from the preset shape, this approach provides large errors. This can be particularly relevant in cases of inhomogeneous microwave delivery or coupling. In these cases, it is possible that different parts of the sensor area (e.g. spatially offset colour centres) have vastly different profiles of the recorded intensity of the fluorescence light such that the respective profiles cannot be described by a single set of analytical functions (e.g., three separate Lorentzians per resonance / energy level in case of a natural abundance Nitrogen doped14N diamond with hyperfine-splitting .

[0031] Furthermore, fitting curves to a dataset is time-consuming and requires high computing resources, especially if many parameters of the model are varied for addressing changing shapes (as outlined above). Cross relation can be calculated faster and requires less computing power. Thus, the devices and methods described herein may provide faster analysis of an electromagnetic field from the sample compared to prior art solutions, especially if the optical sensor includes many pixels requiring a multitude of calculations of respective changes in the detected fluorescence. This may reduce the time required for calculating the electromagnetic fields from 5 to 10 hours (with commonly known techniques) to several seconds (assuming the same number of pixels).

[0032] The quantum device can be provided for measuring an electromagnetic field that is present in 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.

[0033] Further, temperature changes and / or strain / stress within the sample 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.

[0034] 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 008866436 reflected by the sample). In some examples, the microwave radiation interacting with the sample may be generated by the microwave source.

[0035] 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 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.

[0036] The colour centres may be provided only in the sensor area of the quantum sensor device. The quantum device optionally allows 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. This may allow to probe the sample in-line and / or a high throughput in fingerprinting samples. In this way, the data analysis as described herein can match the speed of data generation. Thus, a fast method for imaging and / or measuring an electromagnetic field from a sample is provided. Optionally, the invention allows widefield imaging of the sensor area.

[0037] 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 otherwords, the sample, e.g. the interaction of the sample with the incident electromagnetic radiation, changes a parameter of the incident electromagnetic radiation.

[0038] The parameter of the microwave radiation may refer to the frequency, the phase, the intensity / amplitude, the polarisation (e.g. clockwise or anti-clockwise), the direction of travel of the microwave radiation, the duration of application of the microwave radiation (e.g. a length of a microwave pulse), and / or a time delay between subsequent microwave pulses. The parameter of the microwave radiation can be set using the controller. The microwave radiation may be fully described by a set of parameters. This means that the characteristics of the microwave radiation can be specified by the set of parameters. The plurality of parameters may refer to the set of parameters or a sub-set of parameters.

[0039] The controller generates control signals that can be sent to the microwave source which generates the microwave radiation having the parameters as set by the controller. For example, all or many parameters of the microwave radiation are set and only one, two or more parameters are varied when recording the fluorescent light. In otherwords, all other parameters 008866436 of the microwave radiation are held constant while only one, two or more parameters are varied. In some examples, a single parameter is varied while all other parameters are held constant. As an example, the frequency of the microwave radiation is varied in a first frequency range and a second frequency range whereas all other parameters such as the amplitude, the phase, the polarisation, et cetera are held constant.

[0040] After impinging on the sample, at least one parameter of the microwave radiation 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 changed 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 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.

[0041] 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%.

[0042] 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. Stated 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. 008866436

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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 imaging optics and / or the sample side may face the sample.

[0048] 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 008866436 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.

[0049] 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.

[0050] 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 crystallin 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.

[0051] 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.

[0052] 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 imaging optics.

[0053] 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. 008866436

[0054] 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.

[0055] 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.

[0056] 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.

[0057] The excitation light source may be configured to continuously emit the excitation light during the entire measurement and / or the entire recording. 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.

[0058] 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 008866436 modulator for controlling the excitation light, e.g. the duration and / or start time of the one or more laser pulses.

[0059] 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 in the first parameter range and / or the second parameter range may resonate with transitions from or to the first and second energy levels, respectively. Thus, the microwave radiation in the first parameter range and / or the second parameter range may have an energy (as defined by the set of parameters) that is equal to or similar to an energy gap corresponding to the transition from or to the first and second energy levels, respectively.

[0060] 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.

[0061] The excitation light source, the optical sensor, and the imaging 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.

[0062] The colour centres 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.

[0063] The magnification of the wide-field microscope could be 1x, 10x, 20x, 50x, 100x, 200x or 400x. The magnification can be adjusted, for example, by the magnification of the imaging optics. The imaging can be adjusted by varying the parameters magnification, number of pixels, and size of the optical sensor.

[0064] The optical sensor may be a device for recording two-dimensional images from light by electrical or electronical means. Semiconductor-based optical sensors that can record light up to the mid-infrared range can be used. Examples of optical sensors in the visible and near infrared range are CCD sensors or CMOS (Complementary metal-oxide-semiconductor) 008866436 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 which 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.

[0065] 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.

[0066] 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.

[0067] The imaging optics may 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.

[0068] 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.

[0069] The imaging optics project the colour centres onto the optical sensor. The fluorescent light emitted by a group of colour centres may therefore 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 imaging optics projects a sub-volume of the sensor area onto a respective pixel. The 008866436 fluorescent light emitted by the colour centres in this sub-volume is recorded by the respective pixel.

[0070] 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 the 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.

[0071] The generator of the microwave source may be configured to generate the microwave electromagnetic energy in wavelength ranges having respective energy ranges that corresponds 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 wavelength) 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.

[0072] 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.

[0073] 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.

[0074] 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 008866436 a frequency that is in resonance with the colour centres and 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.

[0075] 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.

[0076] 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 to 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.

[0077] 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 and / or one recording. 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.

[0078] 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. 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. 008866436

[0079] 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 fluorescent light. These two extrema may correspond to first energy level and the second energy level.

[0080] 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.

[0081] 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.

[0082] A recording may refer to recording the electronic signals for a specific parameter set of the microwave radiation (including the parameter in the first parameter range and / or the second parameter range) and / or a specific configuration of the device magnetic field. Optionally, for generating the image of the sample and / or measuring the electromagnetic field from the sample, a plurality of recordings is made whereby, for each recording, a parameter of the parameter set and / or the configuration of the device magnetic field is changed. This allows to detect changes in the interaction of the microwave radiation with the colour centres which can be used for generating the image of the sample and / or for measuring the electromagnetic field from a sample.

[0083] All recordings necessary for generating the image from the recordings may be considered a measurement. For example, a measurement includes all recordings for each variation of the parameter in the first and second parameter ranges.

[0084] A measurement may include a plurality of recordings which are subsequently recorded. For example, the electronic signals for each recording are recorded one after the other (e.g. without or only short interruptions between the recordings). A recording may include obtaining the electronic signals for each pixel. A measurement may include all the information required to generate an image (e.g. using the cross-correlation as described herein). On the other hand, it may not be possible to generate the image based on a single recording). 008866436

[0085] The parameter set may refer 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, frequency modulation (FM) of the microwave radiation, and / or a (periodic) switch between amplitude zero and a predetermined value (e.g. microwave radiation on or off).

[0086] Optionally, only a single parameter of the parameter set is changed for each recording. A change or variation in the parameter may correspond to the change or variation in the value of the respective parameter. For example, a first value of the parameter refers to a first frequency of the microwave radiation and a second value of the parameter refers to a second frequency of the microwave radiation. Of course, the first and second values may refer to a different parameter, for example the intensity of the microwave radiation and / or the phase of the microwave radiation. A value of the parameter may characterize an amplitude modulation of the microwave radiation.

[0087] Further, the device magnetic field may also be characterised by a set of parameters with which the device magnetic field can be described. A set of parameters may be considered a first configuration or a second configuration. In other words, the device magnetic field of the first configuration differs at least in one physical property from the device magnetic field of the second configuration.

[0088] As described above, for generating the image and / or for measuring the electromagnetic field from the sample, a plurality of recordings and / or a single measurement is made whereby a single parameter may be varied for each recording (e.g. sweeping the parameter). Increasing the number of recordings can provide a reduction of an error in the generation of the image and / or in the measurement of the electromagnetic field.

[0089] The parameter that is varied within a given set of parameters is changed in such a value range that the variation in the microwave radiation interacts and / or resonates 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 parameter range refers to a variation of the generated microwave radiation in such a way that at least one of the varied microwave radiations resonates with a transition from or to the first energy level. Similarly, the second parameter range refers to a variation of the generated microwave radiation in such a way that at least one of the varied microwave radiations resonates with the second energy level (as discussed, this may refer to transitions from or to the respective energy level). For example, if the parameter that is varied is the frequency of the microwave radiation, the microwave 008866436 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.

[0090] For example, the parameter is varied over a value 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 parameter range and / or the second parameter range are chosen in that the recorded fluorescent light shows the entire peak or dip over the varied parameter. In other words, the recorded fluorescent light exhibits a baseline. Stated differently, the first parameter range and / or the second parameter 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.

[0091] Optionally discrete values of the parameter in the first parameter range and / or the second parameter range may be used. For example, the first parameter range and / or the second parameter range may be divided into 10, 20, 50, 100, 200, 500, or 1000 (equally) spaced apart values of the parameter. Consequently, 10, 20, 50, 100, 200, 500, or 1000 recordings for the first parameter range and / or 10, 20, 50, 100, 200, 500, or 1000 recordings for the second parameter range are made. The number of recordings made in the first parameter range and / or the second parameter range may correspond to the sampling frequency in the first parameter range and / or the second parameter range. All recordings together may be considered a single measurement.

[0092] It is also possible that the individual values of the parameter in the first parameter range and / or the second parameter range may not be equally spaced apart from each other. Rather, more recordings are made close to the expected extremum in the first parameter range and / or the second parameter range compared to values of the parameter of said of the expected extremum.

[0093] The first parameter range may not overlap with the second parameter range. For example, the first parameter range is offset from the second parameter range in the domain of the respective parameter. It is also possible that the first parameter range and the second parameter range are chosen to be so broad that they overlap.

[0094] For each recording , the electrical signals received from each pixel are recorded. In other words, when a recording is made using a first value of the parameter, the electronic signals of all pixels are recorded, e.g. simultaneously recorded. Subsequently, a further recording of the colour centres is recorded using a second value of the same parameter. Thus, for every value of the parameter of the microwave radiation in the first parameter range and the second parameter, the intensity of the fluorescent light of the colour centres is (simultaneously) recorded. It is to be 008866436 noted that these recordings may not be displayed. Rather, the electronic signals of each recording and for each pixel is further analysed as described below.

[0095] Changes in the electronic signals between the first parameter range and the second parameter range are determined. This means that the electronic signals over the first parameter range are compared to the electronic signals over the second parameter range. The comparison is done by cross-correlating the electronic signals over the first parameter range with the corresponding electronic signals over the second parameter range. This process is repeated for every pixel. Thus, at the end of this process, changes in electronic signal for each pixel are determined. Thus, it is possible to generate an image based on the changes of the electronic signals in each pixel.

[0096] The determination of the changes in the electronic signals for each pixel may correspond to determining shifts between the extrema in first parameter range and the second parameter range. These shifts between the extrema in the first parameter range and the second parameter range can be detected by cross-correlating the first parameter range with the second parameter range. In other words, the quantum device and the methods described herein do not refer to determining an absolute position of an extremum in the first parameter range and / or the second parameter range. Rather, the quantum device and the method described herein determine a shift in the extrema between the first parameter range and the second parameter range. This approach can be less error prone because no absolute position is determined. Rather a relative change is detected.

[0097] It is also possible to record for each pixel graphs, diagrams, and / or plots of the electronic signals (i.e. the intensity of the fluorescent light) over the first parameter range and the second parameter range (e.g. over the frequency of the microwave radiation). The determination of the changes in the electronic signals may then cross-correlating the graphs, diagrams, and / or plots.

[0098] 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 parameter range and the second parameter 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 electromagnetic field.

[0099] The cross-correlation or certain values of the calculated cross-correlation may be connected to a value of electromagnetic field. For example, shifts in the minimum or the maximum of the electronic signals (corresponding to the intensity of the fluorescent light) can thereby be attributed to particular interactions of the microwave radiation and / or the electromagnetic field with the sample. In other words, these changes in the values of the electronic signals 008866436 correspond to changes in the interaction of the microwave radiation and / or the device magnetic field with the sample.

[0100] The plurality of variations of the parameter may correspond to the number of recordings as outlined above. This means, each variation of the parameter corresponds to setting the parameter and taking a recording, e.g. recording the intensity of the fluorescent light emitted by the colour centres (e.g. for each pixel). Then, the parameter is again varied, for example by incrementally increasing the value of the parameter and the same recording is repeated until all variations of the parameter within the first parameter range and the second parameter range are taken.

[0101] The cross-correlation between the electronic signals generated over the first parameter range with the electronic signals generated over the second parameter range may be done for the electronic signals obtained in a single measurement. This may mean that the electronic signals for the first parameter range and the electronic signals for the second parameter range are obtained in a single measurement.

[0102] It is possible that the electrical signals of all pixels are recorded in a format of a matrix. It is case, the calculation of the cross-correlation may include matrix multiplication or other types of calculation methods relating to matrixes. In other words, the calculation of the cross-correlation is simultaneously done for all pixels. However, the electrical signals recorded by an individual pixel are only compared to electronic signals of the same pixel. This means that the method described herein does not compare electronic signals from different pixels. As outlined above, the form or shape of the electronic signals over the varied parameter 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 electronic signals generated by different pixels may not result in useful information from the cross-correlation.

[0103] The cross-correlation is not a parametric method. This means that the cross-correlation is agnostic to the shape of the electronic signals over the parameter ranges. Thus, the crosscorrelation is capable of providing reliable results although the shape of the electronic signals over the parameter ranges can vary significantly between two pixels. It is assumed that the shape of the electronic signals over the parameter ranges between the first and second parameter ranges is similar or identical because the signals are caused by the same group of colour centres (i.e. from the same location and, therefore, subjected to the same electromagnetic field).

[0104] The cross-correlation function may be a discrete cross-correlation. An exemplary formula is given below 008866436

[0105] Thereby, f are the discrete electrical signals over the first parameter range, g are the discrete electrical signals over the second parameter range, n and m are the number of the varied parameter, and N corresponds to the number of variations over the first parameter range and the second parameter range. Optionally, the number of variations in the first parameter range and the second parameter range is the same.

[0106] If the first parameter range and the second parameter range do not overlap, a bias may be added to the first and / or the second parameter ranges for comparing the electronic signals from the first and second parameter ranges. The bias may be selected so that the first parameter range and the second parameter range overlap. In this case, the two parameter ranges can be compared without adding zero-filings in the range between the first and second parameter ranges. Of course, the applied bias is considered when comparing the electric signals from the first parameter range with the electric signals from the second parameter range. For example, the bias is added to the calculated lag or difference in the peaks.

[0107] In an optional embodiment, the parameter is a frequency of the microwave radiation or a time delay between two pulses of the microwave radiation.

[0108] All recordings over the first parameter range and the second parameter range may be considered as corresponding to an optically detected magnetic resonance (ODMR) measurement. Thereby, the parameter that is varied is the frequency of the microwave radiation. In this case, the first parameter range correspond to a first frequency range and the second parameter range correspond to a second frequency range.

[0109] Further exemplary measuring techniques in which the parameter is the frequency of the microwave radiation are coherently averaged synchronized readout (CASR) measurements or AERIS (Amplitude-Encoded Radio Induced Signal) method.

[0110] Further, the parameter may relate to a time of delay between two pulses of microwave radiation or the duration of microwave pulses. In these cases, the first parameter range correspond to a first range of delay times / durations and the second parameter range correspond to a second range of delay times / durations.

[0111] Exemplary measuring techniques are Rabi measurements, Ramsey measurements, or quantum frequency mixing. 008866436

[0112] It is apparent from the above exemplary measuring techniques that not only a single parameter of the microwave radiation is varied. Other parameters may be Simultaneously varied or changed within the same measurements.

[0113] It is also possible that each recording is not only made in the first parameter range and the second parameter range. Rather, further parameter ranges may be measured wherein each parameter range corresponds to an energy level of the colour centres. For example, the first and second parameter ranges correspond to the energy levels of the colour centres that is induced by the component of an external magnetic field that extends in the x-direction. Third and fourth parameter ranges correspond to the energy levels of the colour centres that is induced by the component of an external magnetic field that extends in the y-direction. Fifth and sixth parameter ranges correspond to the energy levels of the colour centres that is induced by the component of an external magnetic field that extends in the z-direction. In this case, it is possible to calculate the external magnetic field in each dimension by calculating the crosssection of corresponding parameter 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.

[0114] 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 sensors. 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.

[0115] It is also possible that the first parameter range and / or the second parameter range cover two or more energy levels of the colour centres. In this case, the curve of the fluorescent light over the varied parameter includes two or more extrema.

[0116] In an optional embodiment, the controller is configured to calculate the electromagnetic field from the sample by determining an extremum of the cross-correlation.

[0117] The extreme 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 peaks 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. 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 after 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 008866436 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.

[0118] 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 extreme in the cross-correlation can be determined.

[0119] In optional embodiment, the controller is configured to fit a curve to the cross-correlation. Optionally, the controller is further configured to determine the extremum of the crosscorrelation as the extremum of the fitted curve.

[0120] This approach may provide more reliable results for determining the extremum in the crosscorrelation. For example, outliers that may have been identified as an extremum are not considered when determining a maximum of fitted curve. The fitting of the curve with the crosscorrelation may be more reliable compared to fitting a curved to the electronic signals over the first parameter range and the second parameter range because less deviation from the expected shape or form of the curve is expected with cross-correlation compared to electronic signals. Further, only a single curve needs to be fitted compared to the approaches of the prior art with which two curves are fitted, namely the curves over the first parameter range and the second parameter range. The fitting of the curve to the cross correlation may be done as known in the prior art.

[0121] 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.

[0122] 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.

[0123] 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 room 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 008866436 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.

[0124] In an optional embodiment, the controller is further configured to use a discrete Fourier- transformation, optionally a Fast-Fourier-transformation or a Nonuniform Fast-Fourier- transformation, for calculating the cross-correlation.

[0125] 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 parameter range and multiply the Fourier-transformed signals with the complex conjugate of the Fourier-transformation of the electronic signals from the second parameter 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.

[0126] In an optional embodiment, the controller is configured to calculate baselines of the electronic signals in the first parameter range and the second parameter range. Optionally, the controller is further configured to subtract the respective calculated baseline from electronic signals in the first parameter range and the second parameter range prior to calculating the cross-correlation.

[0127] The baseline of the electronic signals in the first parameter range and the second parameter range may correspond to values of the recorded intensity of the fluorescent light at which the 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.

[0128] 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 parameter range and / or the second parameter range. A value of the calculated baseline may be subtracted from all electronic signals in the first parameter range and / or the second parameter range. This may correspond to a normalisation of the electronic signals in the first parameter range and / or the second parameter range. This provides better comparison between the electronic signals from the first parameter range and the second parameter range because they do not differ in their respective baselines. 008866436

[0129] In an optional embodiment, the controller is configured to smooth and / or upsample the electronic signals in the first parameter range and / or the second parameter range prior to calculating the cross-correlation.

[0130] 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.

[0131] The smoothing of the signals in the first parameter range and / or the second parameter 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 parameter range and / or the second parameter range. As a result, the noise in the cross calculation can also be reduced.

[0132] The upsampling is done to increase the number of data points in the first parameter range and / or the second parameter range. Upsampling may also be implemented to adjust a sampling frequency in the first parameter range to the sampling frequency in a second parameter range or vice versa. The upsampling may be implemented by interpolating the electronic signals in the first parameter range and / or the second parameter range. Commonly known upsampling techniques and / or method can be used.

[0133] 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 parameter range and / or the second parameter range prior to calculating the cross-correlation.

[0134] Commonly known neural networks can be used. The neural networks can be trained with data that is obtained by running measurements and / or recordings 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 for training the neural network.

[0135] The use of the neural network may optimise to 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. 008866436

[0136] In an optional embodiment, the controller is a field-programmable gate array (FPGA) or an application-specific integrated circuit (ASIC).

[0137] The use of the FPGA or the ASIC can be possible because no curves are fitted to the electronic signals in the first parameter range and / or the second parameter 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, crosscorrelation 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.

[0138] 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.

[0139] 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.

[0140] 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.

[0141] In an optional embodiment, the method of imaging and / or measuring an electromagnetic field from the sample, optionally the steps of determining - for each pixel - changes in the electronic signals by cross-correlating the electronic signals generated over first parameter range with the electronic signals generated over second parameter range and / or calculating the electromagnetic field of the sample based on cross-correlation, is executed in real-time.

[0142] This is possible by using the cross-correlation as described above. The term “real-time” may refer to a maximum duration for imaging and / or measuring an electromagnetic field from the sample, optionally the steps of determining - for each pixel - changes in the electronic signals by cross-correlating the electronic signals generated over first parameter range with the electronic signals generated over second parameter range and / or calculating the electromagnetic field of the sample based on cross-correlation, of 0.1 s, 0.5 s, 1 s, 5 s, or 10 s. 008866436

[0143] Alternatively or additionally, the term “real-time” may refer to speed of imaging and / or measuring an electromagnetic field from the sample, optionally the steps of determining - for each pixel - changes in the electronic signals by cross-correlating the electronic signals generated over first parameter range with the electronic signals generated over second parameter range and / or calculating the electromagnetic field of the sample based on crosscorrelation, such that it is possible to generate the image and / or the measurement of the electromagnetic field 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 electromagnetic field of the sample.

[0144] The imaged and / or measured electromagnetic field 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 electromagnetic field of the sample can be used determine different types of structures within the sample.

[0145] 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.

[0146] 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.

[0147] 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. 008866436

[0148] 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.

[0149] 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.

[0150] This optional embodiment may also be provided by the quantum device and / or the controller.

[0151] 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 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.

[0152] 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 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.

[0153] 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 electromagnetic field 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.

[0154] 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 calculating the electromagnetic field of the sample.

[0155] 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 008866436 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.

[0156] An example of the invention is described in the following:

[0157] The methods and devices described herein refer to an algorithmic implementation that enables the real-time inference of physical properties, for example obtainable from optically detectable magnetic resonance (ODMR) experiments in widefield microscopy using nitrogen vacancy (NV) centres in diamonds. Properties that can be inferred with this techniques described herein are, e.g., magnetic and / or electric fields, temperatures, and strain / stress. The established state of the art is to use numerical optimization approaches that fit analytical profiles to the measured ODMR spectra. The inferred positions of the profiles in the spectrum are then used to calculate the physical properties (e.g., the difference in frequency between the two fluorescence profiles that are associated with the same NV axis in a diamond is proportional to the parallel component of the device magnetic field vector to that axis). The high number of involved free fitting parameters and the inherently iterative nature of the methods makes them prone to error and particularly computationally expensive, with typical computation times for widefield applications regularly exceeding several hours.

[0158] The methods and devices described herein, on the contrary, is by construction non-iterative and non-parametric and can thereby be executed within less than 10 seconds whilst being more precise. To implement this, Fast-Fourier transformation can be used to implement a (weighted) cross-correlation with subsequent peak position identification to determine the frequency difference (lag) between two associated profiles.

[0159] Assuming the lag, Af, of two signals S1 (f) and S2(f) is of interest, wherein both signals stem from an ODMR experiment recording the NV fluorescence (or contrast) as a function of the frequency f of the generated microwave radiation, the following cross-correlation function CCF can be used (efficient notation that allows algorithmic use of fast Fourier transforms): wherein F and F-1are the Fourier transform and its inverse, respectively, and wherein F denotes the complex conjugate of F. The position of the highest peak in the CCF can then be used for the determination of Af which is indicative of the electromagnetic field to be measured. 008866436

[0160] BRIEF DESCRIPTION OF THE DRAWINGS

[0161] The invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which:

[0162] Fig. 1 shows a schematic view of a quantum device;

[0163] 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 ;

[0164] 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;

[0165] Fig. 4 shows graphs of electronic signals generated in a first frequency range (left graph a)) and in a second frequency range (right graph b));

[0166] Fig. 5 shows a graph of a cross-correlation of the graphs of Fig. 4, wherein the baseline was subtracted from both lines prior to the cross-correlation.

[0167] 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.

[0168] DETAILED DESCRIPTION

[0169] Fig. 1 shows an embodiment of a quantum device 10 for imaging a sample 12 and / or measuring 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.

[0170] 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, imaging 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.

[0171] 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 008866436 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.

[0172] The imaging 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.

[0173] 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 a quantum sensors). The NV- centres can be projected onto the optical sensor 32 by the imaging optics 28 which 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.

[0174] 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 field-programmable gate array (FPGA) or an application-specific integrated circuit (ASIC).

[0175] 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.

[0176] 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 imaging optics 28. The objective focuses the incident light onto the NV- centres in the quantum sensor device 18. The light 008866436 emitted by the NV- centres is projected by the imaging 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 .

[0177] 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.

[0178] 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.

[0179] 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.

[0180] 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.

[0181] 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.

[0182] 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 imaging optics 28. In other words, the microwave antenna and the imaging optics 28 008866436 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 imaging optics 28 and the sample holder 16.

[0183] 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 by the sample as well as the microwave radiation directly emitted by the antenna of the microwave source 20.

[0184] 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.

[0185] 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.

[0186] 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 008866436 semiconductor material. The differences in the intensity of the fluorescent light emitted by the NV- centres can be displayed in image.

[0187] 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.

[0188] 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.

[0189] 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.

[0190] 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 and / or recordings. This means that, for a particular measurement, the device magnetic field is constant and may be changed for the next measurement. A recording 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.

[0191] A method for determining a quality of a sample which includes a method of imaging and / or measuring an electromagnetic field from the sample 12 is described in connection with the block the diagram of Fig. 2.

[0192] 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, and intensity of the fluorescent light emitted by the colour centres changes in accordance with changes in the electromagnetic field from the sample 12. 008866436

[0193] 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. In this example, the device magnetic field has a first configuration which describes the orientation and / or the strength of the device magnetic field.

[0194] 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 imaging optics 28, for example using the beam splitter 26 and the objective of the imaging optics 28. The excitation light may be continuously emitted. Alternatively, one or more pulses of the excitation light are generated for exciting the colour centres.

[0195] In step S4, microwave radiation is emitted by the microwave source 20. The emitted microwave radiation may be characterised by a parameter set which describes the physical properties of the microwave radiation. The parameters of the parameter set may relate to the frequency, the intensity, the phase, the modulation, the polarisation, the duration of a microwave pulse, the time delay between microwave pulses, and the like of the microwave radiation. The microwave radiation includes a parameter of a first value, for example a frequency of a certain value, which is within a first parameter range. The first parameter range also covers a value of the parameter (together with the other parameters of the parameter set) 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 first value of the parameter 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.

[0196] 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.

[0197] 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 008866436 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.

[0198] In step S6, steps S3 to S5 are repeated many times whereby, each time, microwave radiation has a value for the parameter different to the value of the parameter as used in any other repetition of steps S3 to step S5. For example, the 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 parameter in the first parameter range and in a second parameter range. The second parameter range covers a value of the parameter (together with the other parameters of the parameter set) 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.

[0199] Prior to step S6, the sampling frequency of the first parameter range and / or the second parameter range can be set. This corresponds to number of repetitions that are made in step S6. Optionally, the chosen values of the parameter in the first parameter range and / or the second parameter range as well as the breadth of the first parameter range and / or the second parameter range are chosen to detect extrema in the electronic signals.

[0200] The first parameter range and / or the second parameter 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.

[0201] As an example of step S6, the parameter is the frequency of the microwave radiation which is swept in the first parameter range (see left graph of Fig. 4) and in the first parameter range (see right graph of Fig. 4). As apparent from Fig. 4, the frequency is 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.

[0202] The solid lines in both graphs of Fig. 4 are taken from the same first pixel and the dashed lines in both graphs of Fig. 4 are taken from the same second pixel. As each pixel corresponds to a sub-volume of the quantum sensor device 18, the first and the second pixels show the intensities of the fluorescent light at two spatially offset positions within the sensor area. The difference in the shapes of the solid and dashed curves is assumed to be due to the difference in the electromagnetic field at the corresponding locations in the sensor area. It is apparent that the shape of the dashed lines and solid lines vary considerably. However, the shapes of the solid lines in the graphs are approximately identical. Similarly, the shapes of the dashed lines in the graphs are approximately identical. Thus, for a given pixel, the curves of the fluorescent light are similar for the different energy levels. However, for each frequency range, the curves of the fluorescent light vary significantly between different pixels. Thus, cross-correlations between 008866436 different energy levels provide useful results whereas cross-correlations between different pixels provide less useful results.

[0203] In optional step S7, baselines of the electronic signals in the first parameter range and the second parameter range are calculated. The respective calculated baselines are subtracted from electronic signals in the first parameter range and the second parameter. Alternatively or additionally, the electronic signals in the first parameter range and / or the second parameter range are smoothed (e.g. by applying derivative filters and / or boxcar mean filters such as Savitzky-Golay or Norris filters / derivatives) and / or are upsampled, e.g. by interpolation of two subsequent electronic signals. Alternatively or additionally, the electronic signals are fed into a neural network which is trained to enhance extrema in the electronic signals and / or remove noise in the electronic signals.

[0204] In step S8, changes in the electronic signals over the various recordings made in step S6 are determined. This may include cross-correlating - for each pixel - the electronic signals (as obtained directly in step S6 or as pre-processed in step S7) in the first frequency range with the electronic signals (as obtained directly in step S6 or as pre-processed in step S7) in the second frequency range. Optionally, the cross-correlation is calculated using a discrete Fast-Fourier transformation as known in the prior art.

[0205] Fig. 5 shows the cross-correlations for the curves of Fig. 4. The solid line corresponds to the cross-correlation between the solid curves of the left and right graphs of Fig. 4. The dashed line corresponds to the cross-correlation between the dashed curves of the left and right graphs of Fig. 4. Due to the more pronounced dips in the intensity of the fluorescent light in the solid lines, the cross correlation of the solid lines shows a clear and sharp peaks. The cross correlation of the dashed lines shows a broad peak. However, in both cases, it is possible to reliably determine the position of the peak of the cross-correlation. This position is equal to a frequency shift between the first and second energy levels which can be proportional to the electromagnetic field from the sample 12.

[0206] In step S9, the electromagnetic field of the sample 12 is calculated for each pixel based on cross-correlation obtained in step S8. For example, 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 parameter range and the second parameter range (e.g. between extrema in the first parameter range and the second parameter range). This shift of the parameter 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 008866436 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.

[0207] 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.

[0208] 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 by 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.

[0209] 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.

[0210] 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. 2. 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.

[0211] 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 . 008866436

[0212] 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.

[0213] 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 light 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.

[0214] 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 set of parameters as described in connection with above step S4. Optionally, the control signals include the parameter to be varied.

[0215] 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.

[0216] 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.

[0217] 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 varied parameter as described in connection with steps S3 to S5.

[0218] In optional step S18, the controller 24 may calculate baselines of the electronic signals in the first parameter range and the second parameter range. The controller 24 may subtract the respective calculated baselines from electronic signals in the first parameter range and the second parameter. Alternatively or additionally, the controller 24 may smooth the electronic signals in the first parameter range and / or the second parameter range (e.g. by applying derivative filters and / or boxcar mean filters such as Savitzky-Golay or Norris filters / derivatives) and / or upsample, e.g. by interpolation of two subsequent electronic signals. Alternatively or 008866436 additionally, the controller 24 may include and / or execute a neural network to which the electronic signals are fed. The neural network can be trained to enhance extrema in the electronic signals and / or remove noise in the electronic signals.

[0219] In step S19, the controller 24 determines changes in the electronic signals over the various recordings made in step S17. This may include cross-correlating - for each pixel - the electronic signals (as obtained directly in step S17 or as pre-processed in step S18) in the first frequency range with the electronic signals (as obtained directly in step S17 or as pre-processed in step S18) 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.

[0220] 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.

[0221] 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.

[0222] 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

1. 008866436CLAIMS:1 . A quantum device for imaging and / or measuring an electromagnetic field from a sample (12), comprising a quantum sensor device (18) including colour centres in a sensor area, the quantum sensor device (18) being configured to be arranged adjacent to the sample (12) to be subjected to the electromagnetic field, the colour centres being configured to emit fluorescent light depending on the electromagnetic field, 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 fluorescent 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, imaging 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 radiation being characterized by a plurality of parameters, 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, and a 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) for varying at least one parameter of the plurality of parameters in a first parameter range in which the first energy level resonates with the microwave radiation and a second parameter range in which the second energy level resonates with the microwave radiation,(ii) record - for each pixel - the electronic signals received from the optical sensor (32) for a plurality of variations of the parameter in the first parameter range and the second parameter range,(iii) determine - for each pixel - changes in the electronic signals by crosscorrelating the electronic signals generated over first parameter range with the electronic signals generated over second parameter range, and(iv) calculate the electromagnetic field of the sample (12) based on the crosscorrelation.

2. The quantum device of claim 1 , wherein the parameter is a frequency of the microwave radiation or a time delay between two pulses of the microwave radiation.0088664363. The quantum device of claim 1 or 2, wherein the controller (24) is configured to calculate the electromagnetic field from the sample (12) by determining an extremum of the crosscorrelation.

4. The quantum device of claim 3, wherein the controller (24) is configured to fit a curve to the cross-correlation, wherein the controller (24) is further configured to determine the extremum of the crosscorrelation as the extremum of the fitted curve.

5. 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.

6. The quantum device of any preceding claim, wherein the controller (24) is further configured to use a discrete Fourier-transformation for calculating the cross-correlation.

7. The quantum device of any preceding claim, wherein the controller (24) is configured to calculate baselines of the electronic signals in the first parameter range and the second parameter range, and wherein the controller (24) is further configured to subtract the respective calculated baseline from electronic signals in the first parameter range and the second parameter range prior to calculating the cross-correlation.

8. The quantum device of any preceding claim, wherein the controller (24) is configured to smooth and / or upsample the electronic signals in the first parameter range and / or the second parameter range prior to calculating the cross-correlation.

9. The quantum device of any preceding claim, wherein the controller (24) is configured to execute a neural network which is trained to enhance extrema and / or remove noise in the electronic signals in the first parameter range and / or the second parameter range prior to calculating the cross-correlation.

10. A method for imaging and / or measuring an electromagnetic field from a sample (12), comprising the steps of arranging a quantum sensor device (18) including colour centres in a sensor area adjacent to the sample (12) to be subjected to the electromagnetic field, the colour centres being configured to emit fluorescent 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 fluorescent light,008866436 projecting, by imaging 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 varying at least one parameter of a microwave radiation to be emitted towards the sensor area over a first parameter range in which the first energy level resonates with the microwave radiation and a second parameter range in which the second energy level resonates with the microwave radiation, the microwave radiation being characterized by a plurality of parameters, recording - for each pixel of an optical sensor (32) - electronic signals for a plurality of variations of the parameter in the first parameter range and the second parameter range, the electronic signals being indicative of an intensity of the light emitted by colour centres, determining - for each pixel - changes in the electronic signals by cross-correlating the electronic signals generated over first parameter range with the electronic signals generated over second parameter range, and calculating the electromagnetic field of the sample (12) based on cross-correlation.

11. A method for determining a quality of a sample (12), comprising the steps of imaging and / or measuring an electromagnetic field of the sample (12) using the method of claim 10 in real-time, determining the quality of the sample (12) based on the imaged and / or measured electromagnetic field of the sample (12).

12. The method of claim 11 , 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).

13. A controller for a quantum device for imaging and / or measuring an electromagnetic field from a sample (12), the quantum device (10) comprising a quantum sensor device (18) including colour centres in a sensor area, the quantum sensor device (18) being configured to be arranged adjacent to the sample (12) to be subjected to the electromagnetic field, the colour centres being configured to emit fluorescent 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) comprises008866436 a first output port configured to be connected to an excitation light source, 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 fluorescent 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, 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, and wherein the controller (24) is configured to(i) control the excitation light source (30) for exciting the colour centres,(ii) control the microwave source (20) for varying a parameter of the microwave radiation over a first parameter range in which the first energy level resonates with the microwave radiation and a second parameter range in which the second energy level resonates with the microwave radiation, the microwave radiation being characterized by a plurality of parameters,(iii) record - for each pixel - the electronic signals received from the optical sensor (32) for a plurality of variations of the parameter in the first parameter range and the second parameter range,(iv) determine - for each pixel - changes in the electronic signals by crosscorrelating the electronic signals generated over first parameter range with the electronic signals generated over second parameter range, and(v) calculate the electromagnetic field of the sample (12) based on the crosscorrelation.

14. The controller of claim 13, wherein the controller (24) is a field-programmable gate array (FPGA) or an application-specific integrated circuit (ASIC).

15. The controller of claim 13 or 14, wherein the controller (24) is further configured to determine quality parameter of the sample (12) based on the calculated electromagnetic field of the sample, wherein optionally the controller (24) is configured to generate a rejection signal if the determined quality parameter is outside a predetermined range and / or to generate a feedback signal based on the determined quality parameter.

16. A computer-implemented method for imaging and / or measuring an electromagnetic field from a sample (12), the quantum device (10) comprising a quantum sensor device (18) including colour centres in a sensor area, the quantum sensor device (18) being configured to be arranged adjacent to the sample (12) to be subjected to the electromagnetic field, the colour centres being configured to emit fluorescent light depending on the electromagnetic field, and008866436 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 of generating 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 fluorescent light, generating control signals to be sent to a microwave source (20) for varying a parameter of the microwave radiation emitted by the microwave source (20) over a first parameter range in which the first energy level is optically excitable and a second parameter range in which the second energy level is optically excitable, the microwave radiation being characterized by a plurality of parameters, 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 a plurality of variations of the parameter in the first parameter range and the second parameter range, determining - for each pixel - changes in the electronic signals by crosscorrelating the electronic signals generated over first parameter range with the electronic signals generated over second parameter range, and calculating the magnetic field of the sample (12) based on the cross-correlation.

17. 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 16.

18. A computer-readable storage medium comprising instructions which, when executed by a computer, cause the computer to carry out the steps of the method of claim 16.

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