Measuring assembly for precisely measuring small angles

Abstract

The invention relates to a measuring assembly (10) for precisely measuring angles between an antenna (12) and a spin system (16) having at least three crystal axes of which the angles to one another are known, the assembly comprising a light source (20) for generating light, a light sensor (26) for detecting a light signal emitted by the spin system (16), and a microwave generator (18) for generating a microwave signal which is emitted towards the spin system (16) by means of the antenna (12). The measuring assembly also comprises a memory (30) for storing data points for the light signal, the data points comprising information regarding contained Rabi frequencies and / or contained magnetic resonance spectra (ODMR spectra), and an analysis unit (32) for evaluating the data points and for ascertaining a measurement value and for determining the angle between the antenna (12) and the spin system (16) from the measurement value. The analysis unit (32) is designed to process Rabi frequencies in order to ascertain information regarding the angle between the spin system (16) and the antenna (12).

Description

[0001] Rhineland-Palatinate University of Technology Kaiserslautern-Landau

[0002] Measuring arrangement for precise measurement of small angles

[0003] The present invention relates to a measuring arrangement for precisely measuring angles and a method for precisely measuring angles by means of a measuring arrangement.

[0004] Measurements of angles between two objects are often desired in industrial environments, but can sometimes be difficult to achieve. This is particularly true for exact or high-precision angle measurements and for determining angles on small objects or in very confined spaces. Angle measurements are important in many industries, particularly in electrical engineering. For example, in semiconductor manufacturing, wafers must be positioned with high precision. Small changes or deviations have a major impact on the production of wafers or computer chips. Therefore, high-precision measurements are necessary. Such measurements, especially of angles, are generally very complex, susceptible to influence, and sensitive to external interference. Even small disturbances in the measuring environment can lead to large deviations. The measurement methods known to date are based either on mechanical measuring methods or on inclination angle measurements orAcceleration measurements. For particularly precise measurements, laser distance measurements of two or three neighboring points are sometimes performed. However, all measurements require space and sometimes involve large detectors. If distance information is required in addition to angle information, other, different measurement systems must always be used, in addition to optical path length measurements. Inclination angle measurements are usually based on an array of acceleration sensors that measure the orientation of the Earth's gravity or gravitational acceleration in three orthogonal axes using miniaturized microelectromechanical systems (MEMS). This results in a vector that can be converted into an angle measurement relative to the Earth's gravity.

[0005] Optical measurement techniques are typically based on measuring transit times or phase shifts, which can be determined interferometrically. However, to determine an angle, this technology requires at least two or three laser beams whose relative path length changes can be converted into an angle signal. These technologies therefore require direct access between the object to be measured and the laser source. Furthermore, they require particularly highly polished or highly reflective surfaces. However, both measurement methods are inaccurate or limited at small and very small distances due to the shorter transit times. Furthermore, the measuring devices are often several centimeters in size and therefore not suitable for measurements in confined spaces.

[0006] Based on the current state of the art, there is still a need for simple and precise determination of angle information. In particular, there is a need for measurement setups that can be used flexibly.

[0007] The present object is achieved by a measuring arrangement having the features of claim 1 and by a method having the features of claim 11 and claim 13.

[0008] In a first aspect, the present invention relates to a measuring arrangement for precisely measuring angular information. The angles are measured between an antenna and a quantum emitter, such as a spin system. The measuring arrangement comprises a light source for generating light with a predetermined emission wavelength, an optional light guide for guiding the light to the quantum emitter, and a light sensor for detecting a light signal emitted by the quantum emitter following optical excitation. The excitation is provided by the light source and a microwave generator, which is also part of the measuring arrangement.

[0009] The measuring arrangement further comprises a microwave generator for generating a microwave signal with a predetermined excitation frequency and pulse length, which is radiated towards the quantum emitter by means of the antenna. Furthermore, the measuring arrangement comprises a memory for storing data points for the measured and detected light signal of the quantum emitter. The memory can be a volatile or non-volatile memory, for example, the internal memory of a processor unit. The data points comprise information on Rabi frequencies contained in the light signal and / or on optically detectable magnetic resonance spectra, so-called ODMR spectra. An analysis unit of the measuring arrangement is configured and designed to evaluate and further process the stored data points and to determine a measured value.It is also configured to determine an angle between the antenna and the quantum emitter based on the measured value and / or the data points. The analysis unit processes Rabi frequencies, which are used to determine the angle between the spin system and the antenna. If necessary, electron spin resonances or excitation frequencies are first determined from the ODMR spectra in the analysis unit if these are not yet available. Preferably, Rabi oscillations are then excited using the electron spin resonances or excitation frequencies in the microwave range and subsequently measured. From these, the Rabi frequencies can then be determined.

[0010] Preferably, the angle between antenna and quantum emitter is determined using a calibration curve or a calibration table from the measured value and / or the determined data points.

[0011] The signal generated in the microwave generator is defined by the area under the pulse curve, which is described by the amplitude and pulse duration (e.g., in a rectangular pulse). The amplitude is constant. The signal is therefore defined by its pulse duration (pulse length), which is predetermined and specified. The pulse duration can be varied for different measurements.

[0012] In a preferred embodiment, the analysis unit of the measuring arrangement is also designed to determine the distance between the antenna and the spin system. This allows the measuring arrangement according to the invention to measure the distance, preferably simultaneously, in addition to the angle measurement.

[0013] The measuring principle according to the invention is based on the fact that a measurement signal is generated by the frequency of brightness differences of a "point source" as a function of the angle to an antenna. The point source is the center of the quantum emitter, in particular the center of an impurity and a defect. This can be, for example, a diamond with a nitrogen vacancy center. The frequency of the brightness fluctuations corresponds to fluctuations in the fluorescent light, which provides information about the angle. It is emitted in all directions in space. The signal can therefore be detected from any direction. Tilts are therefore not problematic, since the direct angle between the B-field (magnetic field) emitting antenna (microwave antenna) and the "point source" (center of the quantum emitter) is always measured.A further advantage is the high spatial resolution, as these fluorescent particles (centers in the quantum emitter) are found in nanodiamonds with a diameter of less than 10 nm. The detector, exciting light source, antenna, and quantum emitter can also be spatially separated.

[0014] The same applies to the distance and its determination accordingly, so that angle and distance can be preferably measured with the measuring principle and the measuring arrangement according to the invention.

[0015] The measuring principle according to the invention, which is reflected by the measuring arrangement, is based on measuring the angle between the quantum emitter (spin system) and the antenna, and optionally preferably also the distance, by determining Rabi frequencies as emitted by (optically) excited quantum emitters. This requires, on the one hand, excitation of the quantum emitter with light and, on the other hand, excitation with a microwave signal with a polarization. The basic idea behind the measuring arrangement is based on the fact that optically excited quantum emitters emit fluorescence, which can be measured by a measuring arrangement. Additional excitation with microwave radiation in the near field induces Rabi oscillations and changes the fluorescence radiation emitted by the quantum emitter.A change in the scalar product of the magnetic microwave field strength at the location of the quantum emitter and the quantization axis, which is determined by the quantum emitter, causes a change in the Rabi frequencies. The resulting Rabi frequencies are proportional to the magnetic field strength and the angle between the polarization of the microwave field and the axis of the quantum emitter. With a constant excitation power of the microwave antenna and a constant microwave frequency and microwave field polarization, a relative measurement is possible. Based on the measured Rabi frequencies and a known Rabi frequency curve as a function of an angle or distance between the antenna and the quantum emitter, the angle or distance can be deduced and precisely determined.

[0016] A quantum mechanical two-level system must exist, referred to as a spin system. This spin system must exhibit the following properties to be suitable for angle measurement and, if necessary, distance measurement:

[0017] 1 . There must be an optical spin polarization.

[0018] 2. Coherent spin manipulation by microwave fields must be possible.

[0019] 3. The spin system must exhibit spin-dependent fluorescence, i.e., emit a light signal dependent on the spin. To measure an absolute angle change, at least three quantum emitters with different but static and known relative orientations to each other must be present, so that their quantization axes span a three-dimensional space.

[0020] One such quantum system that exhibits these properties is, for example, a diamond with nitrogen and vacancies. In this case, the diamond has so-called negatively charged nitrogen vacancy centers. Such a diamond is particularly suitable as a spin system. Such a system is described, for example, in R. Schirhagl, K. Chang, M. Loretz, Ch. L. Degen; “Nitrogen- Vacancy Centers in Diamond: Nanoscale Sensors for Physics and Biology“; Annual Review Physical Chemistry 2014; Volume 65:83-105; DOI: 10.1146 / an-nurev-physchem-040513-103659. Other spin systems are described, for example, in WO 2017 / 213928 A1 and in NIE, Y. et al.: “Manipulation of Spin Polarization Using NV Ensemble in Diamond for Precision; Displacement Detection With an Adjustable Sensitivity“; IEEE SENSORS JOURNAL, 2021 , Vol. 21 :5961-5966. Other suitable spin systems with other defects are known in the literature and are mentioned, for example, in DE 10 2022 100 420 B3.

[0021] What these coherent spin systems have in common is that microwave excitation of spin states leads to so-called Rabi oscillations, whose frequency Q depends on the magnetic field strength BMW along the quantization axis e of the spin system (dot product). The field strength BMW at the location of the spin system strongly depends on the distance d from the radiating antenna. This causes a change in the Rabi frequencies depending on the distance.

[0022] Within the scope of the invention, it was recognized that there is also a dependence between the static magnetic field and the induced Zeemann splittings of the spin states. The induced resonances correspond to the projection, i.e., the scalar product, between the crystal axes or quantization axes of the spin system and the static magnetic field. The coherent spin systems, which emit light upon optical excitation depending on their spin state, can be detected by measuring the fluorescent light. The fluorescent light is the light signal emitted by the spin system due to the optical excitation. Through prior calibration, for example, the angle between the antenna and the spin system can preferably be optically precisely detected. The same applies to the distance. This principle is described in more detail in DE 10 2022 100 420.Reference is made to the content of DE 10 2022 100 420, which explains the physical principles and fundamentals in more detail. This also describes a basic measurement setup, the principles of which are used to measure the angle.

[0023] The invention utilizes the knowledge that, in addition to optical excitation of the energy levels, magnetic excitation of the spin states can also occur, which then (preferably after spin polarization by initial optical excitation) leads to a modified radiation of light by the spin system. For the generated microwave signal with a predetermined pulse length (pulse duration), the measured light signal emitted by the spin system is stored as a data point. By changing the pulse length (pulse duration) of the generated microwave pulses in the microwave generator, a multitude of data points for measured light signals can be generated, which are then stored in the memory. The evaluation of all stored data points using the analysis unit enables the determination of a measured value from which the so-called Rabi frequency is determined.The measured value is characteristic of the angle between the spin system and the antenna from which the microwave signal is transmitted. Preferably, based on a calibration and knowledge of a calibration curve for the angle between the spin system and the antenna, and the generated measured values, the current angle between the antenna and the spin system can be deduced from the measured value obtained. The same applies analogously to the distance measurement.

[0024] In a preferred embodiment, the analysis unit of the measuring arrangement is designed to determine a distance between the spin system and the antenna in addition to an angle measurement. The distance is preferably determined from the measured value. The analysis unit is suitable for processing Rabi frequencies and / or optically detectable magnetic resonance spectra (ODMR spectra) to determine the distance between the spin system and the antenna. When processing the ODMR spectra, microwave resonances, i.e. transitions within the ground state, can be optically detected. For example, optical detection of the resonances can be achieved by comparing the fluorescence intensity under irradiation with a microwave field with the fluorescence intensity without irradiation with a microwave field. A spectrum of the transitions of the ground state, in which the microwave frequency varies, can be evaluated for this purpose.

[0025] In a preferred embodiment, the analysis unit of the measuring arrangement is designed to determine the distance between the spin system and the antenna from the sum of the Rabi frequencies contained in the data points of a measurement.

[0026] In a likewise preferred embodiment, the analysis unit can, due to its suitability, determine the angle between the antenna and the spin system from the relation of several Rabi frequencies or from the relative change of Rabi frequencies.

[0027] In an alternative, likewise preferred embodiment, the analysis unit of the measuring arrangement is designed to process and evaluate at least three Rabi frequencies to determine the angle between the antenna and the spin system. Preferably, four Rabi frequencies can be used to determine the angle. If necessary, redundancy of the information can be used to verify this. This allows the at least three NV axes, i.e., the quantization axes between the axes caused by a nitrogen atom and a nitrogen vacancy in the atomic lattice, to be used. The determination of the fourth axis of the NV centers serves only for verification purposes. This can be based on the fourth Rabi frequency. The analysis unit preferably also processes several Rabi frequencies to determine the angle between the spin system and the antenna.This involves determining the individual angles between the antenna and the axes of the so-called NV centers of the spin system. The term NV center refers to a doping of the spin system in which an impurity (defect) and a defect are introduced. In the special case of a diamond as a spin system, the NV center is formed from a negatively charged nitrogen vacancy center as a point defect in the diamond structure. In this case, a nitrogen atom substitutes for a carbon atom. A defect is formed at a neighboring lattice site. A total of four possible orientations of NV centers can exist in the diamond lattice, whose axes enclose an angle of 109.5°.

[0028] In a preferred embodiment, the measuring arrangement comprises a magnetic field source for generating a static magnetic field acting on the spin system. The static magnetic field preferably has a strength of a few millitesla (mT). In the static magnetic field generated by the magnetic field source, the Zeeman effect leads to a splitting of the spin states of the ground state in the spin system. This allows the individual quantization axes between the impurity and the defect in the quantum emitter to be detected. With a large number of impurity-defect centers (quantum emitters) in a single-crystal diamond, these centers lie on four possible axes. This results in up to eight resonances from the four spatial axes and the possible spin transitions in the spin system using the external static magnetic field.In this way, the resonant frequencies can be easily determined so that they can be used for the microwave field generated by the microwave generator using a microwave signal. The microwave excitation occurs at a selected frequency that coincides with one of the resonant frequencies of the spin system. This facilitates analysis.

[0029] In an alternative, but equally preferred embodiment, the external static magnetic field can be omitted. In a preferred embodiment, the analysis unit is designed to perform a Fourier transformation to determine the measured value from the data points. Using the Fourier transformation, it is possible to separate the existing Rabi frequencies of an ensemble of spin systems, the differences between which are caused by the different orientation of the crystal axes between the impurity and the defect in the spin system. To determine the angle and / or a distance, the measured value that can be read off from the data points after Fourier transformation can be used. In addition to a Fourier transformation, a suitable fitting curve can also be used to infer the individual impurity-defect axes and their measured values.Alternatively and preferably, a mathematical calculation may be performed to determine the angle and / or distance.

[0030] In a preferred embodiment, the analysis unit of the measuring arrangement is also configured to determine the angle and, if appropriate, also the distance between the antenna and the quantum emitter based on the measured value and using a calibration curve or a calibration table from the determined data points. A preferred embodiment of the measuring arrangement provides that the analysis unit is configured to evaluate at least one calibration curve between Rabi frequency and angle and / or distance.

[0031] In a preferred embodiment, the antenna of the measuring arrangement is a microwave antenna. It is configured and designed to generate electromagnetic microwave pulses in its near field. Preferably, the antenna is positioned so close to the spin system that the spin system is in the near field of the magnetic field generated by the microwave antenna.

[0032] In a preferred embodiment, the microwave generator for generating microwave pulses is designed such that a feed signal with a predetermined frequency is generated for the antenna. The feed signal is transmitted to the antenna, preferably via connecting lines, which can be implemented as cables. The frequency of the feed signal emitted by the antenna is preferably greater than 1 GHz. When used with spin systems, it has been found that the frequency lies between 2.4 GHz and 3.5 GHz. This frequency range is particularly suitable when using diamond lattices with nitrogen vacancies. The frequency is very preferably between 2.65 GHz and 3.1 GHz. It has also proven to be positive that the frequency can depend on the strength of a static magnetic field acting on the spin system.

[0033] The microwave signal generated by the microwave generator preferably has a pulse length between 1 ns and 10 ps. For practical operation, a pulse duration between 10 ns and 5 ps has proven particularly preferred. Preferably, the microwave generator generates and uses microwave pulses with different pulse durations, with the entire range being generated successively in small steps, for example, 10 ns steps. It is also conceivable to cycle through the pulse duration in a different number of steps or with other changes. The choice of the different pulse durations depends in particular on the accuracy of the measurement and the total measurement time available. This may vary considerably for individual applications.

[0034] In a preferred embodiment, the light source of the measuring arrangement is a laser light source. The light source preferably generates laser light with a wavelength of less than 637 nm. Several studies have shown it to be advantageous if the wavelength of the laser light is between 480 nm and 580 nm. A wavelength between 500 nm and 530 nm is particularly advantageous. The wavelength of the laser light is preferably selected so that it lies outside, preferably below, the wavelength of the light emitted by the spin system in response to excitation with laser light. The wavelength of the laser light is therefore preferably outside the fluorescent range.

[0035] In a preferred embodiment, the light from the light source, in particular the laser light from a laser light source, is coupled into the optical waveguide and guided to the spin system. The optical waveguide can be, for example, a fiber optic cable. Preferably, the optical waveguide is also used to transmit the fluorescent light emitted by the spin system. Consequently, the light emitted by the spin system (as a result of optical excitation) can be guided to the light sensor via the optical waveguide.

[0036] In a preferred embodiment, the optical waveguide comprises an optical filter to transmit fluorescent light having a wavelength greater than the wavelength of the light generated by the light source and preferably to filter out scattered light, preferably outside the fluorescence range of the spin system.

[0037] The optical filter can be integrated into the optical fiber. It is also possible for the optical fiber to be interrupted by the optical filter. This means that a first section of the optical fiber leads to an optical filter, the light then passes through the optical filter, and is then guided into a second section of the optical fiber.

[0038] A preferred embodiment provides that the spin system is an optically active spin system with a spin degree of freedom. The quantum emitter is preferably a diamond vacancy center. A spin system composed of diamonds with nitrogen vacancies is particularly preferred. For example, the spin system can be a diamond crystal with nitrogen vacancies dissolved in an aqueous solution. The aqueous solution is preferably applied to a support, which is more preferably non-metallic. Within the scope of the invention, it has been shown that a glass support is very preferred, to which the diamonds with nitrogen vacancies, dissolved in water, are applied.

[0039] A further preferred embodiment of the measuring arrangement has a light sensor, which is an optical detector for receiving light or a light signal. The light sensor is preferably a photodiode. It can be a photon counter, for example a single-photon counter, or an avalanche diode. Other suitable light sensors are conceivable for measuring the fluorescence emitted by the spin system. The stated object is also achieved according to the invention by a method for measuring angles and preferably additionally for precisely measuring small distances. This can involve, on the one hand, continuous measurement of the fluorescence during the transmission of a microwave signal, or, on the other hand, comparative measurement of the fluorescence with and without microwave pulses. The method embodiments represent alternative measurement methods.

[0040] In this method, the measurement is carried out between an antenna, preferably a radio-frequency antenna or microwave antenna, and a spin system, with the antenna and spin system being part of a measuring arrangement. The method is also based on the knowledge that in a spin system, the electrons can be excited, on the one hand, by light, and on the other hand, by a microwave signal and a resulting magnetic field. Furthermore, the method is based on the knowledge that the magnetic field and its polarization are proportional to the angle between the antenna generating the magnetic field and the spin system. If the magnetic field conditions are kept constant, the fluorescence (light radiation) emitted by the emitter depends on the angle between the antenna and the spin system.

[0041] The method according to the invention provides that light with a specific emission wavelength is emitted from a light source to a spin system. The wavelength of the light is preferably between 480 nm and 637 nm. In a further step, while the spin system is exposed to light, a microwave signal with a predetermined pulse length is emitted to the spin system from an antenna, in particular a radio-frequency antenna. The fluorescent light emitted by the spin system in response to the optical excitation is measured while the microwave signal is being emitted. During this time, at least one data point for the measured light signal (fluorescence signal) is stored. Through further measurements, a data set of several light points is thus recorded and stored, wherein the data set includes the light intensity as a function of time.For example, depending on the desired accuracy, multiple data points can be acquired. However, at least this many data points are required to represent the qualitative course of Rabi oscillations. A further step in the process involves evaluating the data points using an analysis unit. This involves determining a measured value from the data points that is characteristic of the angle between the antenna and the spin system. The measured value represents a Rabi frequency, from which the angle can be determined.

[0042] A further, optional step of the method can preferably provide for the angle and / or distance between the antenna and the spin system to be determined from the measured value using a corresponding calibration curve or a calibration table. For this purpose, corresponding measured values ​​are preferably generated during a calibration with several predetermined angles or distances that are known, preferably at least three. A calibration curve can be extrapolated from these values, for example, using a fitting curve or fitting function.

[0043] This method reflects a continuous measurement of the data points to determine the distance.

[0044] An equally preferred embodiment of the method provides further steps that include evaluating the measured value and determining and evaluating Rabi frequencies to determine the distance between the antenna and the spin system. This is based on the finding that the distance between the antenna and the spin system can be clearly deduced from the measured Rabi frequencies and the data points. Alternatively, the distance can also be determined based on the evaluation of ODMR spectra.

[0045] The alternative method according to the invention initially comprises emitting light with a predetermined emission wavelength, whereby the light strikes the spin system. This results in optical excitation of the spin system. The light source is then switched off again in a next step. A further step involves emitting a microwave signal with a predetermined pulse length or pulse duration and a predetermined (defined) excitation frequency from the antenna to the spin system and re-emitting light using the light source to excite the spin system. The pulse duration can be very long, even almost infinite. A further step involves measuring a light signal (fluorescence) emitted by the spin system using a light sensor. A data point is stored for the measured light signal and used to determine a measurement signal. In a further step, the pulse duration of the microwave signal is changed.Optionally, the light source can be switched off beforehand. The previous steps are then repeated for the desired number of measurement signals or data points to be determined. Thus, a light signal is determined depending on the pulse duration of the microwave signal.

[0046] The method further comprises a step of evaluating the measured data points using an analysis unit and determining a measured value from the measured data points. The data points and the resulting measured value are characteristic of the angle between the antenna and the spin system, since the other boundary conditions are kept constant.

[0047] In a further, optional step of the method, the angle or the individual angles between the antenna and the spin system or the impurity centers of the spin system are preferably determined from the measured value by means of one or more calibration curves.

[0048] In a preferred embodiment of the method, further optional steps are included which comprise determining the distance from the measured value, for which purpose Rabi frequencies or ODMR spectra are evaluated.

[0049] In a further preferred embodiment of the method, a static magnetic field is generated that acts on the spin system. This splits the occurring resonance frequencies according to the individual spatial axes of the crystal lattice. This simplifies the analysis and determination of the angle and / or distance. In preferred embodiments, the antenna is coupled to a static magnetic field or to a static magnetic field source, so that movements of the antenna cause the same movements of the magnetic field source. The antenna and magnetic field source then move synchronously, with their separation remaining constant.

[0050] The invention is described and explained in more detail below using selected embodiments in conjunction with the accompanying drawings. They show:

[0051] Fig. 1 is a schematic representation of the measuring arrangement according to the invention;

[0052] Fig. 2 shows a preferred embodiment of the optical part of the measuring arrangement;

[0053] Fig. 3 a schematic diagram of the crystal structure of diamond with embedded spin system in four possible orientations;

[0054] Fig. 4 is a graphical representation of the relative fluorescence (ODMR spectrum) versus microwave frequency in an external static magnetic field;

[0055] Fig. 5 a graphical representation of the relative fluorescence as a function of the pulse duration of the applied microwave signal (Rabi oscillation);

[0056] Fig. 6 is a schematic representation of the first measuring arrangement;

[0057] Fig. 7 is a schematic representation of the second measuring arrangement;

[0058] Fig. 8a, 8b each show a schematic representation of the sequence of a method according to the invention.

[0059] Fig. 1 shows the inventive measuring arrangement 10 for measuring an angle and optionally also for measuring a distance between an antenna 12, which is designed as a microwave antenna 14, and a spin system 16. The spin system must exhibit optical spin polarization, coherent spin manipulation by microwave fields, spin-dependent fluorescence, and possess at least three fixed quantization axes. Such a spin system is preferably a diamond with a negatively charged nitrogen vacancy center. The spin system can be applied to a carrier, which can be made of glass, for example, while dissolved in a liquid.

[0060] The microwave antenna 14 is fed by a microwave generator 18, which generates a microwave signal with a predetermined pulse length.

[0061] A light source 20 generates light with a predetermined emission wavelength. The light source is preferably a laser light source 22, which emits laser light and optically excites the spin system. The light from the light source 20 can be guided to the spin system 16 by means of an optional optical fiber or light guide 24, as shown in Fig. 2. A light sensor 26, which can be designed as a photodiode 28 or avalanche diode, receives light signals emitted by the spin system, which are caused by changes in the energy states in the spin system. The received light signals are transmitted by the light sensor 26, for example as electrical signals, to a memory 30, which can be designed as a storage unit and integrated into an analysis unit 32. The measured light signals are stored in the memory in the form of data points, with the pulse length of the exciting microwave signal preferably also being stored.Of course, the memory can also be an external storage unit that can be connected to the analysis unit 32. It does not have to be integrated into the analysis unit.

[0062] The analysis unit 32 evaluates the stored data points and determines a measured value from them. The analysis unit 32 is preferably further configured to determine the angle and, if appropriate, the distance between the antenna 12 and the spin system 16 based on the measured value, preferably using at least one calibration curve stored in the memory 30. Typically, one calibration curve is used for the angle, or one for each angle of the NV centers, and another for the distance. The measuring arrangement is thus configured to measure the angles between the antenna 12 and the individual NV centers of the spin system 16, which is preferably a diamond with nitrogen vacancies.

[0063] A magnetic field source 34 generates a static magnetic field 36, which acts on the spin system 16 and leads to a splitting of the spin states of the ground state.

[0064] In the embodiment shown here, antenna 12, light source 20, and light sensor 26 are arranged close to one another, with antenna 12 and light source 20 radiating onto spin system 16 from the same direction. It is also possible for antenna 12, light source 20, and / or light sensor 26 to be arranged at different angles or spatial directions relative to the spin system. Since the spin system radiates as a point source, the position of the light source and light sensor is irrelevant. They are independent of each other. The position of the antenna is also independent of the arrangement of the light source and light sensor.

[0065] Fig. 2 shows a particular embodiment of the optical part of the measuring arrangement 10 and the spin system 16. In this embodiment, an optical waveguide 24 is used to redirect light from the light source 20 to the spin system 16. The optical waveguide 24 is simultaneously used to receive light signals emitted by the spin system 16 and transmit them to the light sensor 26. This is connected to the analysis unit 32 so that the light signals can be evaluated.

[0066] An optical coupling unit 38 enables the input and output of the received light. The optical coupling unit 38 comprises a partially transparent mirror 40 and an optical filter 42. Light generated in the light source 20 is guided by an optional optical waveguide 24 to the partially transparent mirror 40 and there deflected towards the spin system 16, wherein the light is guided in the direction of arrow 44 in the optical waveguide 24. Light signals induced by fluorescence from the spin system also enter the optical waveguide 24 and are guided in the direction of arrow 46 to the partially transparent mirror 40, which they pass through without reflection and reach the optical filter 42. The optical filter allows light emitted by the spin system with a wavelength greater than a cutoff wavelength to pass through. The filter can be an optical longpass. The cutoff wavelength is, for example, 637 nm.The optical filter 42 filters out stray light outside the desired range of the fluorescent light. It can particularly filter wavelengths below the cutoff wavelength, with the cutoff wavelength preferably being above the wavelength of the laser light emitted by the light source 20, which is configured as a laser light source 22.

[0067] After passing through the optical filter, the emitted light (fluorescent light) reaches the light sensor 26, which is coupled to the optical waveguide 24.

[0068] Fig. 3 shows a schematic diagram of a spin system 16. It is a single-crystal diamond with a multitude of NV centers that are detected simultaneously. The NV centers lie in all four possible axes. This results in up to eight resonances in an external magnetic field from the four spatial / quantization axes and the two spin transitions m s = 0 to m s = +1 or m s = 0 to m s= -1. An exemplary spectrum with eight spatial axes is shown in Fig. 4.

[0069] An important property of the NV centers in the diamond lattice that enables these measurements is the coherence of the spin states, which are characterized by relaxation time and dephasing time. As can be seen from Fig. 5, the amplitude of the oscillations decreases exponentially due to this relaxation and dephasing. To measure this oscillation, a spin system is therefore necessary in which this relaxation time is large compared to the bandwidth of the rest of the measurement setup, in particular the signal generators (microwave generator and generator for a light source) and the detectors. Within the scope of the invention, it was recognized that with the procedure described here and suitable measurement sequences, a very precise angle measurement can be performed even for small angles or small angle changes. Additional or alternative distance determination in the nanometer and micrometer ranges is possible with high precision.All that is required is a prior calibration to be able to determine the angle or distance between the microwave antenna and the spin system from the Rabi frequencies.

[0070] Measurement types

[0071] With the measuring arrangement according to the invention, different types of measurements can be performed, each enabling the precise measurement of angles or extremely small distances. In principle, the individual methods can be divided into pulsed optical measurement with an external magnetic field, continuous optical measurement with an external magnetic field, pulsed optical measurement without an external magnetic field, and continuous optical measurement without an external magnetic field.

[0072] The basic measurement principle of the invention is based on brightness differences in a diamond as a spin system with nitrogen vacancy centers (NV centers) in the diamond lattice and their changes as a result of the movement of an antenna structure relative to the diamond lattice. This allows information to be obtained about the angle and, if applicable, the distance between a Rabi-frequency emitting structure, the so-called nitrogen vacancy center or its axis in the diamond lattice, and an antenna structure emitting a polarized microwave field.

[0073] Fig. 6 shows a measurement setup of a measuring arrangement 10 with an external magnetic field source 34, a spin system 16, a microwave generator 18 with antenna 12, a light source 20 with optical fiber 24, and a photodiode 28 as a light sensor 26 for receiving the light emitted by the spin system 16. The light signal generated by the light source 20 comprises both a brightness component and a modulation. The light signal is guided by the optical fiber 24 from the light source 26 to the spin system 16 and back to the light sensor 26. The measuring arrangement 10 is controlled by a control unit 54, which also controls the analysis unit 32. Since the antenna 12 is located away from the microwave generator 18, the microwave signal is transmitted via a microwave fiber 52.

[0074] The arrangement shown in Figure 6 essentially corresponds to the measuring arrangement 10 from Figure 1.

[0075] In a static external magnetic field, a splitting of the spin states of the ground state is induced. This occurs according to the so-called Zeeman effect according to:

[0076] AE = hg s G B m s B ext ■ e NV .

[0077] Here, AE denotes the shift of the energy level due to the Zeeman effect, h the Planck constant, g s ~ 2 the landing factor, = 9.274 ■ 10' 24 J / T the Bohr magneton, B ext the external magnetic

[0078] Magnetic field and ewv the unit vector of the NV axis and the nitrogen vacancy quantization axis, respectively.

[0079] In other words, the splitting is directly proportional to the scalar product B ext ' ^NV > thus to the magnetic field component along the NV axis, as shown in Fig. 3. The proportionality constant y = hg s G B is 2.8 MHz / G.

[0080] In the case of an ensemble, i.e., a multitude of NV centers in a spin system, for example, a single-crystal diamond, which are detected simultaneously, NV centers are present along all four possible axes. This results in up to eight resonances in an external magnetic field from the four spatial axes and the two spin transitions m s = 0 -» m s = ±1. A corresponding spectrum with these eight resonances is shown in Fig. 3.

[0081] Basically, the Rabi frequency fl~jl • B RF, i.e., the frequency of the oscillation, is proportional to the magnetic field component along the axis of the magnetic moment of the NV centers. These, in turn, differ for the four possible spatial directions (see Figure 3). Therefore, oscillations with only one frequency are possible when split in a static magnetic field. Without the external field, four superimposed oscillations are excited. The excitation can preferably occur simultaneously or, preferably, sequentially and independently. These have different amplitudes and frequencies, which depend on the polarization of the microwave field in relation to the respective NV axes as well as the strength of the microwave field.

[0082] If an external magnetic field from the magnetic field source 34 is present, up to eight resonances (ODMR resonances) are split in the ODMR spectrum. Specifically, for this measurement method, a constant static background magnetic field (magnitude and direction) must be present at the location of the spin system 16, which is preferably formed as a diamond. The magnetic field ensures a Zeeman splitting of the m s = ±1 levels, so that a total of eight resonances can be measured separately in an ODMR spectrum. The exact relative orientation or strength of the static external magnetic field does not need to be known.

[0083] Four resonances correspond to the transitions of m s = 0 m s = -1 and four resonances correspond to the transitions of m s = 0 -» m s = +1 corresponding to the projection (scalar product) between the NV axis (quantization axis or crystal axis in diamonds) and the external static magnetic field B ext. In total, up to 8 ODMR resonances are split by the external magnetic field.

[0084] If Rabi oscillations are now observed at three (or four) ODMR resonance frequencies of the transition m s = 0 -» m s = -1 or m s = 0 -» m s = +1 are measured simultaneously or consecutively, a specific Rabi frequency results for each excitation frequency (which corresponds to an ODMR resonance frequency) at a specific distance between the RF-emitting structure (antenna 12) and NV centers in the diamond lattice (corresponding to spin system 16). Thus, for a fixed RF power, each ODMR resonance has a specific Rabi frequency at a specific angle and a specific distance between the antenna and spin system 16 (diamond).

[0085] The measured Rabi frequencies depend linearly on the magnetic component of the exciting field strength (~B RFof the RF field and on the other hand on the polarization of the microwave field to the respective NV axis (~B RF , ' NV)- With the change in the relative distance between the RF-emitting structure (antenna 12) and the diamond (i.e. spin system 16), the Rabi frequency changes. This allows an absolute distance to be determined with the help of a calibration. This is described, for example, in DE 10 2022 100 420. Here, the Rabi frequency (assuming constant polarization and a fixed RF power) changes uniformly for all resonances for a fixed angle. They increase or decrease by the same percentage. Thus, the sum of the Rabi frequencies can also be used as a distance function using a calibration curve. The distance is therefore measured by measuring the Rabi frequencies with a known RF power and then comparing them with a calibration curve.

[0086] For the measurement of an angle, the property is exploited that the Rabi frequency of an NV center depends on the polarization of the RF field and each NV axis (i.e. the scalar product between the polarization axis of the microwave field and the NV axis (~e NV i ■ B RF 1 )).

[0087] If the angle between an antenna and a NV axis in the diamond (spin system 16) is changed, the Rabi frequency also changes due to the changed scalar product. Since a total of up to four axes (of the transition m s = 0 -» m s = -1 or m s = 0 -» m s= +1 ) can be measured, which are in a fixed ratio to one another. This assumes that the radiation is constant over the frequency range or calibrated accordingly. In total, Rabi frequency measurements on at least three NV axes are required to determine the angle. The fourth axis is redundant and is used only for verification and control. The actual determination of the angle is preferably carried out by simulation and comparison of simulated Rabi frequencies with the measured data, or with the help of calibration curves, or with the help of another evaluation method.

[0088] In the simulation, the orientation of NV center axes (e wl / ,i -axes) to the magnetic field axis (ß RF 1 -axis) and the field strength B RF J _ varies.

[0089] For this method, a constant magnetic field must be applied to the diamond (spin system 16), the strength and direction of which need not be known. However, it must be static with respect to the diamond's spin system 16. The strength and direction must be chosen such that all eight resonances are split. The antenna structure of the antenna 12 or microwave antenna 14, as an RF-emitting element, is moved relative to the spin system 16 for the measurement.

[0090] The fluorescence of the NV centers in the diamond (spin system 16) resulting from the optical excitation is then preferably detected using a photodiode 28, camera, single-photon counter, or similar device. The light can be directed to the light sensor either via lenses or objectives or similar devices, or via a fiber coupling or an optical waveguide 24. With a fiber-coupled solution, the optical setup can be kept compact, and optical excitation and detection can be performed via the fiber optic cable (optical waveguide 24). This enables measurements in hard-to-reach or narrow locations.

[0091] The measurement of an angle is carried out by measuring Rabi oscillations at at least three ODMR resonances of the transition m s = 0 -» m s = -1 or m s = 0 -» m s = +1 and their relative changes in the Rabi frequencies to each other.

[0092] An alternative measurement method is the measurement setup 10 shown in Figure 7. In this case, no external magnetic field from a magnetic field source is used. If no external magnetic field is present, two resonances typically occur at 2.865 GHz and 2.875 GHz in suitable spin systems, for example, in so-called HPHT diamonds, due to mechanical strains and lattice defects. These correspond to the transition m s = 0 -> m s = -1 and +1 .

[0093] If one of these resonances is excited with a resonant (magnetic) microwave field, four Rabi oscillations can be measured, corresponding to the scalar product between the polarization axis of the microwave field and the four axes of the NV centers. Without an external magnetic field, the RF frequencies for these transitions coincide. Only the strength, and thus the oscillation frequency, differs. The Rabi oscillations can be measured as a superimposed brightness signal depending on the microwave pulse length.

[0094] Since there are a total of 2 resonances, a total of 8 Rabi oscillations are generated, which are present as a kind of beat and are evaluated.

[0095] Using a Fourier transform, four oscillation frequencies can be determined, corresponding to the four Rabi frequencies. Alternative methods, such as fit curves or mathematical calculations that evaluate the beat signal, can also be used. By considering the four Rabi frequencies, a distance and an angle (in a fixed reference system, characterized by the polar angle and azimuth angle) can be measured.

[0096] The distance can be determined by the Rabi frequency of a known NV axis or by the sum of the Rabi frequencies of all NV axes and using a calibration curve, since the microwave power drops sharply with increasing distance, especially in the near field.

[0097] The angle can be detected by the relative change of individual Rabi frequencies. Changing the angle between the diamond (spin system 16) and the antenna changes the relative polarization between the diamond or spin system and the antenna. This leads to a changed scalar product between the individual NV axes and the antenna.

[0098] An alternative measurement method also uses a static magnetic field 36, which is preferably generated by a coil 56 or a permanent magnet as the magnetic field source 34. The measurement is based on the measurement and evaluation of ODMR resonances to determine the distance and the evaluation of Rabi frequencies to determine the angle or angle information. A corresponding measurement setup is shown in Figure 7. The integration of the magnetic field source 34 in the form of the coil 56 is made possible by a sensor head 50, whereby the distance between the antenna 12 and the magnetic field source 34 always remains constant.

[0099] For this method, a static magnetic field is generated at the location of the diamond using coil 56 or an external permanent magnet. The strength and direction of the magnetic field do not need to be known. However, the magnetic field must be as homogeneous as possible at the location of the spin system (e.g., diamond). The relative distance between the magnetic field source (coil or permanent magnet) and a spin system (diamond) is measured using the splitting of the Zeeman states of NV centers. This is possible because the static magnetic field strength at the location of the spin system or diamond depends on the distance between the NV center and the magnet.

[0100] The measurement of distances in this method is based on measuring the Zeeman splitting of the ODMR resonances by applying an external magnetic field. Since the strength of the magnetic field decreases with increasing distance, a distance profile can be measured or a relative distance can be calculated. Using calibration curves or calculations, an absolute distance can also be defined and measured here.

[0101] In this method, angles are measured by measuring Rabi frequencies at the ODMR resonances of the NV axes. By changing the angle between the NV axes and the polarization of the microwave field (dot product), the Rabi frequency changes depending on the angle. This dependence is different for the four NV axes and for each axis. Changing the Rabi frequency allows for relative angle determination.

[0102] However, only three out of four Rabi frequencies need to be in the state of transition m s = 0 -» m s = -1 or m s = 0 -» m s = +1. A calibration curve can also be used to measure or determine an absolute angle.

[0103] In addition to the first two measurement setups and methods, this method has the advantage that the measured ODMR resonances can also be used, if necessary, to verify the distance and thus improve the distance accuracy. Preferably, the distance measurement is performed not only on one NV axis, but on three NV axes. This is done analogously to the above measurement of the sum of the Rabi frequencies without a magnetic field – but here with a magnetic field and therefore sequentially on at least three NV axes. The measurement of all (up to) eight Rabi frequencies can also be used to independently verify the distance information obtained from the ODMR resonance measurements and to improve the distance measurement accuracy. By measuring all eight Rabi frequencies, additional measurement data is generated, which can either be summed or individually compared with calibration curves.By averaging the results, the measurement accuracy can be increased and an error measure, such as standard deviation, variance, etc., can be specified.

[0104] Figure 8a shows the basic sequence of a method according to the invention for precisely measuring an angle between an antenna 12 and a spin system 16 using a measuring arrangement 10. The method comprises several steps. In a step S10, light with a specific emission wavelength is emitted from a light source to the spin system. The light can, for example, be transmitted at the light source guide. A step S12 of emitting a microwave signal with a predetermined pulse duration from an antenna 12 to the spin system 16 is also part of the method, as is a step S14 of measuring a light signal emitted by the spin system with a light sensor during the emission of the microwave signal. In a further step S16, a data point for the measured signal is stored.

[0105] Steps S14 and S16 may be repeated in a desired number of sequences until a desired number of data points are generated and stored during the transmission of the microwave signal according to step S12.

[0106] An evaluation step S18 evaluates the data points using an analysis unit. According to a step S20, a measured value is determined from the data points. In a step S22, Rabi frequencies are determined and evaluated to determine the angle between the antenna and the spin system. A further step S24 concerns determining the angle between the antenna and the spin system from the measured value. This can preferably be done using a calibration curve.

[0107] Further optional steps can also be part of the method according to the invention or follow it. They are shown in dashed lines in Figure 8a. In step S26, a distance between the antenna and the spin system is determined from the measured value. A step S28, which is also optional, concerns the determination and evaluation of Rabi frequencies or ODMR spectra to determine the distance between the antenna and the spin system.

[0108] Also optionally, in a step S30, a static magnetic field can be generated that acts on the spin system 16. Optionally, the corresponding magnetic field source can be integrated into a sensor head of the measuring arrangement. Even if step S30 is arranged at the end of the method, this step can also be performed at a different point in the sequence of steps of the method. Figure 8b shows an alternative method according to the invention for precisely measuring an angle between an antenna and a spin system using a measuring arrangement. In a step S50, light with a predetermined emission wavelength is emitted from a light source to a spin system.

[0109] Step S52 involves turning off the light source.

[0110] In the subsequent transmission step S54, a microwave signal with a predetermined pulse duration is transmitted from the antenna to the spin system. A step S56 involves retransmitting light with the predetermined emission wavelength from the light source to the spin system. In a step S58, a light signal emitted by the spin system is measured with a light sensor during the transmission of light.

[0111] A data point storage step (S60) follows to store data points for the measured light signal. An optional step (S62) involves turning off the light source. Alternatively, the light source can remain on. In a step (S64), the pulse duration of the microwave signal is changed.

[0112] Steps S50 to S64 can be repeated until a desired number of data points have been determined and saved.

[0113] Step S66 involves evaluating the data points using an analysis unit and determining a measured value from the data points. In a further step S68, the angle between the antenna and the spin system is determined from the measured value and by determining and evaluating the corresponding Rabi frequencies contained in the data points.

[0114] In an optional, further, but equally preferred step S70, the distance between the antenna and the spin system can be determined from the corresponding measured value. Rabi frequencies or ODMR resonances are determined and evaluated to determine the distance.

[0115] Also optionally available with this method is the generation of a static magnetic field that acts on the spin system. The magnetic field source can act directly on the spin system and be stationary. Alternatively, the magnetic field source can be integrated into a corresponding sensor head and move with the antenna.

[0116] The invention has been comprehensively described and explained with reference to the drawings and the description. The description and explanation are to be understood as exemplary and not restrictive. The invention is not limited to the disclosed embodiments. Other embodiments or variations will become apparent to those skilled in the art upon use of the present invention and upon careful analysis of the drawings, the disclosure, and the following claims.

[0117] In the patent claims, the words "comprising" and "having" do not exclude the presence of further elements or steps. The undefined article "a" or "an" does not exclude the presence of a plurality. A single element or unit can perform the functions of several of the elements mentioned in the patent claims. An element, unit, or device can be partially or completely implemented in hardware and / or software. The mere mention of some measures in several different dependent claims should not be understood to mean that a combination of these measures cannot also be used advantageously. Reference signs in the patent claims are not to be understood as limiting. Reference signs

[0118] 10 Measuring arrangement

[0119] 12 Antenna

[0120] 14 Microwave antenna

[0121] 16 Spin System

[0122] 18 microwave generator

[0123] 20 light source

[0124] 22 Laser light source

[0125] 24 optical fibers

[0126] 26 Light sensor

[0127] 28 photodiodes

[0128] 30 storage

[0129] 32 Analysis Unit

[0130] 34 Magnetic field source

[0131] 36 static magnetic field

[0132] 38 coupling unit

[0133] 40 partially transparent mirror

[0134] 42 optical filters

[0135] 44 Arrow

[0136] 46 Arrow

[0137] 48 Arrow

[0138] 50 sensor head

[0139] 52 microwave guides

[0140] 54 Control unit

[0141] 56 coil

Claims

Patent claims 1. A measuring arrangement (10) for precisely measuring angles between an antenna (12) and a spin system (16) with at least three crystal axes whose angles to each other are known, comprising - a light source (20) for generating light having a predetermined emission wavelength; - a light sensor (26) for detecting a light signal emitted by the spin system (16); - a microwave generator (18) for generating a microwave signal with a predetermined excitation frequency and pulse duration, which is radiated by means of the antenna (12) in the direction of the spin system (16); - a memory (30) for storing data points for the measured and detected light signal, wherein the data points comprise information on Rabi frequencies contained in the light signal and / or optically detectable magnetic resonance spectra (ODMR spectra); - an analysis unit (32) for evaluating the stored data points and for determining a measured value and for determining the angle between the antenna (12) and the spin system (16) from the measured value; wherein the analysis unit (32) is designed to process Rabi frequencies to determine angle information between the spin system (16) and the antenna (12).

2. Measuring arrangement (10) according to claim 1, characterized in that the analysis unit (32) is designed to determine the distance from the measured value and to process Rabi frequencies and / or ODMR to determine the distance between the spin system (16) and the antenna (12).

3. Measuring arrangement (10) according to claim 1 or 2, characterized in that the analysis unit (32) is designed to determine the distance from the sum of the Rabi frequencies contained in the data points of a measurement.

4. Measuring arrangement (10) according to one of the preceding claims, characterized in that the analysis unit (32) is designed to determine the angle between the antenna (12) and the spin system (16) from the relation or the relative change of the Rabi frequencies.

5. Measuring arrangement (10) according to one of the preceding claims, characterized in that at least 3 Rabi frequencies are processed to determine the angle.

6. Measuring arrangement (10) according to one of the preceding claims, further comprising a magnetic field source for generating a static magnetic field acting on the spin system (16), wherein the magnetic field source is preferably a permanent magnet or a coil.

7. Measuring arrangement (10) according to one of the preceding claims, characterized in that the analysis unit (32) is designed to determine the angle from the measured value by means of a calibration curve or a mathematical calculation or to carry out a Fourier transformation in order to determine the measured value from the data points.

8. Measuring arrangement (10) according to one of the preceding claims, characterized in that the analysis unit (32) is designed to evaluate a calibration curve with relations between Rabi frequency and distance and / or a calibration curve with relations between Rabi frequencies and angles between antenna and spin system.

9. Measuring arrangement (10) according to one of the preceding claims, characterized in that an optical waveguide (24) guides the light from and / or to the spin system (16) and that light from the light source (20) is preferably coupled into the optical waveguide (24) and guided to the spin system (16), and preferably emitted light from the spin system (16) is guided to the light sensor (26) by means of the optical waveguide (24), wherein particularly preferably the optical waveguide (24) comprises an optical filter (42) in order to transmit fluorescent light with a wavelength greater than the wavelength of the light generated by the light source (20) and to filter out scattered light outside the fluorescence range of the spin system (16).

10. Measuring arrangement (10) according to one of the preceding claims, characterized in that the spin system (16) is an optically active spin system with spin degrees of freedom, preferably the spin system (16) comprises diamonds, very preferably diamonds with color centers, particularly preferably diamonds with nitrogen vacancy centers.

11. A method for precisely measuring an angle between an antenna (12) and a spin system (16) by means of a measuring arrangement, comprising the following steps: a) emitting light with a predetermined emission wavelength from a light source (20) to a spin system (16); b) emitting a microwave signal with a predetermined pulse duration from an antenna (12) to the spin system (16); c) measuring a light signal emitted by the spin system (16) with a light sensor (26) during the emission of the microwave signal; d) storing a data point for the measured light signal; e) Repeating the above steps c) and d) for a desired number of data points during the transmission of the microwave signal; f) Evaluating the data points by means of an analysis unit (32); g) Determining a measured value from the data points; h) Determining and evaluating Rabi frequencies to determine the angle between the antenna (12) and the spin system (16); and i) Determining the angle between the antenna (12) and the spin system (16) from the measured value.

12. Method according to the preceding claim, characterized by the further steps: Determining the distance between the antenna (12) and the spin system (16) from the measured value; and Determination and evaluation of Rabi frequencies or ODMR spectra to determine the distance between antenna (12) and spin system (16).

13. A method for precisely measuring an angle between an antenna (12) and a spin system (16) by means of a measuring arrangement (10), comprising the following steps: a) emitting light with a predetermined emission wavelength from a light source (20) to a spin system (16); b) switching off the light source (20); c) emitting a microwave signal with a predetermined pulse duration from an antenna (12) to the spin system (16); d) re-emitting light with the predetermined emission wavelength from the light source (20) to the spin system (16); e) measuring a light signal emitted by the spin system (16) with a light sensor (26) during the emission of light; f) storing a data point for the measured light signal; g) optionally switching off the light source (20); h) changing the pulse duration of the microwave signal; i) repeating steps a) to h) for a desired number of data points; j) evaluating the data points by means of an analysis unit (32); k) determining a measured value from the data points; and l) determining the angle between the antenna (12) and the spin system (16) from the measured value and by determining and evaluating Rabi frequencies.

14. Method according to the preceding claim, characterized by the further steps: Determining the distance between the antenna (12) and the spin system (16) from the measured value; and Determination and evaluation of Rabi frequencies or ODMR to determine the distance between antenna (12) and spin system (16).

15. The method according to any one of claims 11 or 13, comprising the further step: Generating a static magnetic field acting on the spin system (16).

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