Automatic resonance control for an NV magnetometer

Abstract

The present invention relates to a method (100) for determining an external magnetic field (B) using an NV magnetometer (1) having auto-resonance control, as well as to an NV magnetometer (1) of this type and the use of one or more NV magnetometers (1) of this type for magnetic field gradient measurements.

Description

Technical Field

[0001] The present invention relates to a method for determining an external magnetic field using an NV magnetometer having auto-resonance control, as well as an NV magnetometer of this type and the use of one or more NV magnetometers of this type for magnetic field gradient measurement.

Background Art

[0002] The diamond nitrogen-vacancy center is one of over 100 known defects in the diamond lattice. These defects are impurities in the pure carbon lattice of diamond. The diamond nitrogen-vacancy center is also referred to as the NV center. Quantum sensors such as NV magnetometers utilize the extreme sensitivity of quantum systems to the environment, making it possible to create significantly improved sensors. The NV center forms a microscopic compass via the spin of an electron by capturing an additional electron. By accurately manipulating and measuring the state of this NV spin, even the smallest changes in the surrounding magnetic field can be measured. This technique is called NV magnetometry and is based on the interaction between the NV center and the surrounding magnetic field. The presence of a magnetic field appears as a change in the energy of the spin state of the NV center. The effect of the magnetic field can be easily recognized from the change in the microwave excitation spectrum of the NV center.

[0003] The decisive advantage of NV magnetometry results from the well-known behavior of the NV center spin transition frequency, which provides clear information about the strength and direction of the magnetic field. This ability to provide self-calibrated quantitative data, combined with very high reproducibility (all NV centers are identical), is an important feature of NV magnetometers. The main advantage of NV magnetometers is their high sensitivity to small signals. The sensitivity of an NV magnetometer to a static magnetic field depends in particular on the density of NV centers in the diamond chip, the quantum coherence of the NV centers, and the efficiency of optical readout. Changes in the magnetic field, temperature, and / or pressure shift the magnetic resonance of the NV center ground state used for magnetic field measurement by the NV magnetometer. This limits the dynamic range of the NV magnetometer and degrades the signal-to-noise ratio (SNR).

[0004] The paper by H Clevenson et al. in Appl. Phys. Lett. 112, 252406 (2018) discloses a robust scale-factor-free vector magnetometer that simultaneously tracks the Zeeman splitting resonances of diamond nitrogen-vacancy centers (NV centers) in diamond using a closed-loop frequency-locking scheme. Nevertheless, it would be desirable to further increase the dynamic range and bandwidth of the NV magnetometer with respect to detectable magnetic field changes, and to improve the measurement SNR while suppressing temperature and pressure fluctuations and enabling an extension to gradient magnetic field measurements. Summary of the Invention Means for Solving the Problems

[0005] An object of the present invention is to provide an NV magnetometer that enables an increase in dynamic range, an expansion of bandwidth with respect to detectable magnetic field changes, and an improvement in SNR in measurements.

[0006] This object is a method for determining an external magnetic field using an NV magnetometer having an automatic resonance control, wherein the NV magnetometer has sensor materials having NV centers with respective spin states m s = 0, m s = ±1, and the resonance frequency f s between the spin states m s = 0 and m ± = ±1 and the difference f ± of the resonance frequencies f + - f - is dependent on the external magnetic field B, and the method - recording a single resonance signal V MW to determine the resonance frequency f SB by frequency-modulated microwave radiation emitted onto the sensor material in a frequency band based on the microwave frequency f ± and the carrier frequency f SR-LIA , wherein the frequency band addresses two magnetic resonances in succession, and the microwave frequency f MW and the carrier frequency f SBA step of selecting and recording, - The resonance frequency f ± And a double resonance signal V having a dispersion form and a linear range around DR-LIA Are recorded, with f such that both magnetic resonances are excited simultaneously MW ±f SB =f ± The microwave frequency f is selected and recorded to be compatible with MW And the carrier frequency f SB A step of selecting and recording, - The demodulated signal V DR-LIA Determining the slope of the linear range as the scalar factor α from - By the evaluation unit, the demodulated signal V with resonance emission of microwave radiation due to an external magnetic field change DR-LIA Via, the resonance frequency f ± The detuning Δ B =V DR-LIA Observing / α, - The observed detuning Δ B Using a controller including a control algorithm based on, the frequency band f MW ±f SB Is such that the detuning Δ B Even after it occurs, this detuning Δ B The resonance frequency f of the NV centers present in ± Remains within the range of, the frequency band f MW ±f SB Controlling, - By the evaluation unit, the distance 2*f between the two frequency bands SB And the detuning Δ B Determining the external magnetic field B from, is achieved by a method including.

[0007] The term "sensor material" refers to a material having NV centers. This is, for example, diamond.

[0008] The spin states m s =0, m s =±1 and, the spin states m s =0 and m s =±1 and the resonance frequency f of the transition between± For a more detailed explanation, please refer to FIG. 1.

[0009] The term "magnetic resonance" refers to the excitation of a higher energy spin state in the NV center and thus the absorption of microwave radiation at the resonance frequency f. ± During the transition to the ground state, the corresponding radiation is emitted again. Magnetic resonance can be measured, for example, in an absorption spectrum or an emission spectrum.

[0010] In this regard, the carrier frequency is a fixed frequency whose amplitude, phase position or frequency changes in the rhythm of the modulation frequency depending on the modulation method. For example, in frequency modulation, the frequency changes. The carrier wave frequency is added again when the signal is demodulated.

[0011] The so-called "scalar factor α" corresponds to the slope of the demodulated signal V in the linear range around the resonance frequency having a zero crossing. DR-LIA Depending on the influence of the external magnetic field, the zero crossing of the demodulated signal V DR-LIA can be shifted at that frequency because the external magnetic field shifts the actual resonance frequency compared to the resonance frequency without the influence of the external magnetic field. This shift is called the resonance detuning Δ. B By using a control algorithm to repeatedly control the operating point of the NV magnetometer at the point of the steepest slope (the maximum value of α) of the demodulated signal, an improved signal-to-noise ratio of the measurement signal can be obtained.

[0012] In this regard, the control algorithm can be installed and executed as a software program on the controller, and the microwave frequency f MW is the detuning Δ observed by the evaluation unit. BSo that it can be controlled according to a control algorithm in response thereto, the controller is connected to an evaluation unit and a microwave transmitter for emitting microwave radiation via data or control lines in order to excite magnetic resonance. In this regard, the evaluation unit can be configured as a processor connected to a storage medium so that it can execute a corresponding evaluation program and store the evaluated data.

[0013] In the NV magnetometer according to the present invention, an intelligent control algorithm including the hardware configuration necessary for this purpose ensures that the frequency of microwave excitation required for high-sensitivity sensor operation remains within the magnetic resonance range.

[0014] Using the method according to the present invention, the NV magnetometer can operate with an increased dynamic range, an expanded bandwidth for detectable magnetic field changes, and an improved SNR in measurements. The above advantages also enable magnetic field gradient measurements using one or more such NV magnetometers.

[0015] In one embodiment of the method or the NV magnetometer, the control is - a step of comparing the demodulated signal V VIA with the setpoint r = 0, and - a step of calculating the deviation e = r - V DR-LIA = - V DR-LIA , and - a step of using the controller to shift the frequency band of the microwave radiation in the opposite direction by Δf MW .

[0016] By continuously adjusting the operating point of the NV magnetometer, the dynamic range of the NV magnetometer is significantly increased. After changes in magnetic field or temperature that can exceed the resonance range, the time-consuming search for resonances in a wide frequency spectrum is thus no longer necessary. The bandwidth of the NV magnetometer also increases accordingly.

[0017] In a preferred embodiment of this method or the NV magnetometer, the controller controls according to the rule Δf MW is an integral software-based controller (5) that controls according to [n]=K*(e[0]+e[1]+…+e[n]), where K is the proportionality coefficient of the controller, and i = 0, 1, …, n are iteration steps. Here, the proportionality factor K is preferably equal to 1 / α.

[0018] In one embodiment of this method or the NV magnetometer, the controller has a control period Tc. After the control period Tc, the microwave frequency f MW is controlled again using the controller, and the control period Tc is 1 μs to 10 s, preferably 0.05 s to 1 s, more preferably 0.5 s. A short control period Tc enables tracking of a rapidly changing magnetic field signal, but setting the frequency band may cause dead time and thus limit the bandwidth of the NV magnetometer. In addition, when the control period Tc becomes long, the optimal operating point (resonance point / zero crossing) cannot be properly maintained, resulting in deterioration of the signal-to-noise ratio SNR. Therefore, a control period Tc = 0.5 s is particularly preferred.

[0019] In a preferred embodiment of this method or the NV magnetometer, the signal generator generates a signal having a microwave frequency f MW and a further signal generator generates a frequency-modulated signal having a carrier frequency f SB , a modulation frequency f m , and a modulation amplitude f d , and f SB (t)=f SB +f d *cos(2πf m t), where t is the time having respective outputs.

[0020] In a preferred embodiment of this method or the NV magnetometer, the two signals are frequency mixed by a frequency mixer, and the microwave radiation emitted onto the sensor material includes two frequency bands f MW +f SB (t) and f MW -f SB (t), and f SB (t) is f MW -fSB It is phase-shifted by π at (t). Preferably, the microwave frequency f MW and the carrier frequency f SB are, with respect thereto, such that two frequency bands are each resonant with the resonance frequency f ± so as to simultaneously excite both magnetic resonances.

[0021] In a preferred embodiment of the method or the NV magnetometer, both frequency bands are emitted with individually adjusted outputs. By being able to adjust the outputs of both frequency bands separately, the difference in the scalar factors of the single resonance spectrum can be minimized, thereby maximizing the suppression of temperature and pressure changes of the double resonance signal. Here, depending on the embodiment of the hardware configuration of the NV magnetometer, the output can be adjusted individually by a programmable attenuator or by adjusting the output of a signal generator.

[0022] The present invention further relates to an NV magnetometer for determining an external magnetic field B, configured to perform the method for automatic resonance control according to any one of the preceding claims, - A sensor material having an NV center having resonance frequencies f s =0, m s =±1 and between the spin states m s =0 and m s =±1, and the difference f ± of the resonance frequencies f ± is such that f + -f - depends on the external magnetic field B, and a sensor material, - A microwave transmitter for exciting magnetic resonance at the resonance frequency f MW by frequency-modulated microwave radiation emitted onto the sensor material in a frequency band based on the microwave frequency f SB and the carrier frequency f ± wherein the microwave frequency f MW and the carrier frequency f SB are such that the frequency band addresses two magnetic resonances in succession with a single resonance signal V SR-LIAselected for recording, microwave frequency f MW and carrier frequency f SB such that both magnetic resonances are excited simultaneously with f MW ±f SB =f ± A microwave transmitter selected for recording the double resonance signal V DR-LIA and, - A laser for emitting in continuous wave mode with a wavelength in the range of 510 - 540 nm for continuous initialization and readout of the spin state - A suitable detector, preferably an optical detector, for recording frequency - modulated fluorescence from the sensor material - A lock - in amplifier for demodulating the fluorescence, wherein one or both magnetic resonance excitations result in a signal V ± having a dispersive form and a linear range around the resonance frequency f SR-LIA or V DR-LIA - An evaluation unit for observing the detuning Δ DR-LIA = V ± / α of the resonance frequency f B through the demodulated signal V DR-LIA - A controller for controlling the frequency band f B such that, using a control algorithm based on the observed detuning Δ MW ±f SB remains within the range of the resonance frequency f B of the NV centers present in this detuning Δ B even after the detuning Δ ± has occurred. The frequency band f MW ±f SB is provided with a controller for controlling it Regarding an NV magnetometer, the evaluation unit is provided for determining the external magnetic field B from the distance 2*f SB between the two frequency bands and the detuning Δ B

[0023] ​​​In the NV magnetometer according to the present invention, an intelligent control algorithm including the hardware configuration necessary for this purpose ensures that the frequency of the microwave excitation required for high-sensitivity sensor operation remains within the magnetic resonance range.

[0024] The NV magnetometer according to the present invention enables an increase in the dynamic range, an expansion of the bandwidth for detectable magnetic field changes, and an improvement in the SNR in measurements. The above advantages also enable magnetic field gradient measurements using one or more such NV magnetometers.

[0025] In this regard, due to its special properties, the sensor material is preferably diamond.

[0026] In one embodiment, the microwave transmitter includes a signal generator for generating a signal having a microwave frequency f MW and a further signal generator for generating a frequency-modulated signal having a carrier frequency f SB , a modulation frequency f m , and a modulation amplitude f d , where f SB (t) = f SB + f d *cos(2πf m t), and t is the time having respective outputs.

[0027] In a further embodiment, the signal generator is configured to adjust the output of the signal, or the signal generator has an attenuator connected upstream for individual output adjustment.

[0028] The present invention further relates to the use of one or more NV magnetometers according to the present invention for magnetic field gradient measurements. The gradient measurement method is a measurement of the components of the gradient magnetic field, for example, the gradient of the magnetic field. In this context, the vector components are registered simultaneously using two sensors (in this case, two NV magnetometers) positioned at a fixed distance apart. The gradient measurement method is used in geomagnetics. Gradient measurements require accurate and fast measurements, which are made possible by the NV magnetometer according to the present invention and the corresponding method according to the present invention.

[0029] It should be clearly noted that expressions that exclusively use "at least" are avoided as much as possible to improve readability. Rather, indefinite articles ("one", "two", etc.) should generally be understood as "at least one", "at least two", etc. unless it is clear from the context that they mean an "exactly" specified number.

[0030] In this regard, it should also be mentioned that in the context of this patent application, the term "in particular" should always be understood as introducing optional preferred features. Therefore, this expression should not be understood as "specifically" nor as "namely".

[0031] It should be understood that the features of the above or the solutions described in the claims can also be combined, individually or cumulatively, departing from the reference in the claims, if applicable, so as to be able to achieve the advantages and effects that can be achieved in this case.

[0032] In addition, further features, effects and advantages of the present invention are described with reference to the accompanying drawings and the following description. The components correspond at least substantially with respect to their functions in the individual figures, where they are indicated by the same reference signs, and these components are numbered and need not be described in all figures.

Brief Description of the Drawings

[0033]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Mode for Carrying Out the Invention

[0034] FIG. 1 shows a schematic diagram of the spin states of the NV centers in the sensor material 2 of the NV magnetometer 1, the dependence of the energy levels on the magnetic field B, temperature T and pressure p, and their resonance and microwave frequency f MW with microwave excitation at, where f MW+ represents the microwave frequency of the excitation of the resonance frequency f + and f MW- represents the microwave frequency of the excitation of the resonance frequency f - . The spin ground state is specified by m s =0, and the two excited spin states are specified by m s =1 and m s =-1, respectively, depending on the orientation of the spin with respect to the external magnetic field. Magnetic resonance

Number

[0035] f ± = D(T,p) ± γB Fluctuations in temperature and pressure can be separated from changes in the magnetic field if both resonance frequencies f ± are known and their difference is proportional only to the external magnetic field B by subtracting the two resonance frequencies from each other.

[0036] f + - f - = 2γB Here, γ is the magnetic gyration ratio of the NV centers in the sensor material 2.

[0037] Figure 2 shows a schematic diagram of (a) magnetic resonance optically detected under emission of frequency-modulated microwave radiation on the NV centers, and (b) the V DR-LIA signal demodulated by the lock-in amplifier 3. The magnetic field measurement method is based on the following techniques.

[0038] Lock-in detection: (Frequency) modulation of the emitted microwave (microwave frequency f MW and carrier frequency f SB ), and subsequent demodulation of the optically detected magnetic resonance by the lock-in amplifier 3. The demodulated signal V DR-LIA of the magnetic resonance has a distributed form and is linear around the resonance frequency (see Figure 2a).

[0039] Scalar factor α: Here, the demodulated signal V DR-LIAThe slope of the linear range (the "scalar factor") must first be determined. Then, microwaves are emitted to resonate. If the resonance frequency changes due to a change in magnetic field, temperature, or pressure, the detuning from the resonance frequency can be evaluated via the signal from the lock-in amplifier 3. When evaluating the differential signal of two magnetic resonances, the influence of temperature T and pressure p, and thus any (resonance) detuning due to a pressure or temperature change ΔT, is eliminated, such that only the influence of the external magnetic field as (magnetic) detuning has the following contribution. Δ B =V DR-LIA / α.

[0040] Figure 2 shows (a) the signal flow diagram of the NV magnetometer 1 according to the present invention, and (b) a schematic diagram of the frequency portion (frequency band) of the microwave radiation emitted onto the sensor material 2 in the first embodiment of the magnetic field measurement method. In Figure 2a, the signal generator 61 generates a signal having a frequency f MW , and a further signal generator 62 generates a frequency-modulated signal having a carrier frequency f SB , a modulation frequency f m , and a modulation amplitude f d .

[0041] f SB (t) = f SB + f d cos(2πf m t) Next, the signal is frequency-mixed in the output coupler 92 such that the signal emitted by the antenna 10 onto the sensor material 2, for example, diamond, contains the following frequency portions.

[0042] f MW + f SB + f d cos(2πf m t) and f MW - f SB + f d cos(2πf m t + π) As can be seen from the figure, the frequency mixing results in a phase difference of π or 180° between the two frequency portions. The system parameters f MW and f SBThe frequency components are each selected to resonate with the transitions

Number

[0043] Fig. 3 shows, in a second alternative embodiment of a magnetic field measurement method having an alternative hardware configuration of the NV magnetometer 1 compared to the configuration shown in Fig. 2, (a) a signal flow diagram of the NV magnetometer 1 according to the present invention, and (b) a schematic diagram of the sensor material 2 and the frequency components (frequency bands) of the microwave radiation emitted onto the diamond here. The method shown in Fig. 3a is based on the same functional principle as Fig. 2a, but here the output of the frequency band dealing with magnetic resonance can be adjusted individually. This is either by means of the programmable attenuator 7 or by adjusting the outputs of the signal generators 61, 62 generating the microwave frequencies.

[0044] Each frequency band is emitted onto the sensor material 2 via the respective antenna 10, and the resulting magnetic resonance (fluorescence FL) is measured via the respective receiver 8 and converted into the double resonance signal V DR-LIA by means of the respective lock-in amplifier 3 having a frequency mixer 31 and a low-pass filter 32. To generate two separate frequency bands, the circuit according to Fig. 2a comprises a corresponding output splitter 91 upstream of the programmable attenuator and respective output combiners 92 for generating the microwave radiation of the respective frequency bands emitted by the respective antennas 10. By being able to adjust the outputs of both frequency bands separately, the difference in the scalar factor α of the single resonance spectrum V SR-LIA can be minimized, whereby the double resonance signal V DR-LIAThe suppression of temperature and pressure changes can be maximized. The modulation phase in Fig. 3b is shown as 0 or π over each frequency portion.

[0045] Fig. 4 shows (a) the single resonance signal V as a function of the microwave frequency f that depends on the resonance detuning Δ B due to the magnetic field change, (top: before change, bottom: after change), (b) the single resonance signal V as a function of the microwave frequency f that depends on the resonance detuning Δ MW due to the pressure and temperature changes, (top: before change, bottom: after change), and (c) a schematic diagram of the demodulated signal V SR-LIA (double resonance signal) resulting from the addition of both single signals V T . To understand the influence of magnetic field, temperature, and pressure changes on the demodulated signal V MW , it is useful to consider the individual parts of the magnetic resonance (single resonance signal V SR-LIA ). From this, the following conclusions can be drawn. SR-LIA The π or 180° relative modulation phase between the two frequency portions results in a vertical mirroring of the single resonance signal V DR-LIA . DR-LIA The single resonance signals V SR-LIA are added so as to reinforce with the change in the magnetic field, while the changes in temperature and pressure result in different signs of the single resonance signal V

[0046] SR-LIA , and thus they are added so as to cancel each other out.

[0047] The double resonance signal V SR-LIA therefore depends only on the change in the magnetic field. The detuning Δ SR-LIA from the resonance frequency caused by the change in the magnetic field can be expressed as follows. Δ

[0048] DR-LIA B = B VDR-LIA / α VDR-LIA / α .

[0049] From this, the following measurement protocol can be derived. ​

[0050] Two magnetic resonance single resonance spectra V SR-LIA are recorded → f + and f - (Determination of the resonance frequency during calibration) Double resonance spectrum V DR-LIA is recorded → determination of the scalar factor α System parameters f MW and f SB The frequency part is f + and f - is fixed as if it is at → continuous determination of the magnetic field using the following formula 2γB = f + -f - +2V DR-LIA / α Figure 5 shows (a) the signal flow diagram of the controller's control algorithm and (b) the resonance detuning Δ of the demodulated signal due to the magnetic field change (left) and the backshift by the control algorithm B The control algorithm is based on the feedback loop shown in Figure 5a. This is based on step 3 of the measurement protocol described above

[0051] The change in the magnetic field results in a resonance detuning Δ B Resonance detuning Δ B results in a change in the output signal of the control system S (see the left side of Figure 5b).

[0052] Next, the output is compared with the setpoint r = 0, and the deviation e = r - V DR-LIA =-V DR-LIA is calculated. In this regard, the controller 5 operates at discrete time intervals, that is, every T C seconds

[0053] Next, the controller 5 (by adjusting the system parameters f MW and f SB ) changes the frequency band in the opposite direction by Δf MW ​Shift only (see the right side of Fig. 5b). Here, an integrated software-based controller 5 that controls according to the following rules is used.

[0054] Δf MW [n]=K(e[0]+e[1]+…+e[n]) Here, K is the proportionality factor of the controller, and i = 0, 1, …, n are the iteration steps. In this regard, the proportionality factor K should be selected as follows to eliminate the deviation (e = 0): K = 1 / α. The following is preferably applied to the control period T C A short control period enables tracking of a rapidly changing magnetic field signal, but may limit the bandwidth of the NV magnetometer 1 because setting the frequency band causes wasted time. In addition, a long control period cannot properly maintain the optimal operating point (resonance point / zero crossing), thus degrading the signal-to-noise ratio. For example, a control period of T C = 0.5 s can be used. The output signal of the control system 2γB = f + -f - + 2V DR-LIA / α Regarding, f ± indicates the position of the frequency band after the last operation of the controller 5.

[0055] Fig. 6 shows an embodiment of the NV magnetometer 1 according to the present invention, which includes a sensor material 2, a lock-in amplifier 3 having a frequency mixer 31 and a low-pass filter 32, an evaluation unit 4, a controller 5 having a control algorithm executed on the controller, and a microwave frequency f MW For a signal having a signal generator 61, a carrier frequency f SB , a modulation frequency fm and a modulation amplitude f d A microwave transmitter 6 having a signal generator 62 for a frequency-modulated signal having, a programmable attenuator, and a single resonance signal V SR-LIAIt includes an optical detector (e.g., a light receiver) for recording. Further, the NV magnetometer can include an output splitter 91, an output coupler 62, and an antenna 10 (not shown here) for emitting microwave radiation on the sensor material 2 (see FIGS. 2a and 3a for this). In addition, the NV magnetometer 1 includes a laser 11 for emitting in continuous wave mode with a wavelength in the range of 510 - 540 nm for continuous initialization and readout of the spin state.

[0056] FIG. 7 is a method 100 according to the invention for determining an external magnetic field using an NV magnetometer 1 with auto-resonance control, where the NV magnetometer 1 has a sensor material 2 with an NV center having resonance frequencies f s = 0, m s = ±1 and for transitions between the spin states m s = 0 and m s = ±1, and the difference f ± of the resonance frequencies f ± is dependent on the external magnetic field B, and a single resonance signal V + - f - is recorded in step 110 for determining the resonance frequency f MW by frequency-modulated microwave radiation emitted on the sensor material 2 in a frequency band based on the microwave frequency f SB and the carrier frequency f ± , where the frequency band is selected such that the microwave frequency f SR-LIA and the carrier frequency f MW and the carrier frequency f SB are selected to address two magnetic resonances in succession, recording step 110; and a double resonance signal V ± having a dispersion form and a linear range around the resonance frequency f DR-LIA is recorded in step 120, where the microwave frequency f MW ± f SB = f ± is selected such that both magnetic resonances are excited simultaneously, recording step 120; and the demodulated signal V MW and the carrier frequency f SB are selected, recording step 120; and the demodulated signal V DR-LIAStep 130 of determining the slope of the linear range as the scalar factor α from, and the demodulated signal V accompanied by the resonant emission of microwave radiation due to the external magnetic field change by the evaluation unit 4 DR-LIA through, the resonant frequency f ± of the detuning Δ B = V DR-LIA / α is observed in step 140, and using the controller 5 including a control algorithm based on the observed detuning Δ B to keep the frequency band f MW ± f SB within the range of the resonant frequency f B of the NV centers present in this detuning Δ B even after the detuning Δ ± occurs, step 150 of controlling the frequency band f MW ± f SB< and step 160 of determining the external magnetic field B from the distance 2*f SB between the two frequency bands and the detuning Δ B by the evaluation unit 4. In this regard, step 150 of controlling includes step 152 of comparing the demodulated signal V DR-VIA with the set value r = 0, step 154 of calculating the deviation e = r - V DR-LIA=- V DR-LIA , and step 156 of shifting the frequency band of the microwave radiation in the opposite direction by Δf MW using the controller 5, showing an embodiment of method 100. In addition, the further steps and means of claims 3 to 10 can be implemented in method 100 according to the present invention (not shown in FIG. 7).

[0057] It should be explicitly noted that in this regard, the features of the solutions described above or in the claims and / or the drawings can also be combined so that, where applicable, the corresponding features, effects, and advantages described as cumulative can be implemented or achieved.

[0058] It should be understood that the above exemplary embodiments are only the initial embodiments of the present invention. In this regard, the embodiments of the present invention are not limited to this example.

Description of Symbols

[0059] 1 NV magnetometer 2 Sensor material (diamond) 3 Lock-in amplifier 31 Frequency mixer 32 Low-pass filter 4 Evaluation unit 5 Controller 6 Microwave transmitter 61 Microwave frequency f MW Signal generator for a signal having 62 Carrier frequency f SB , modulation frequency f m and modulation amplitude f d Signal generator for a frequency-modulated signal having 7 Programmable attenuator 8 Detector (e.g., photoreceiver) for recording a single resonance signal V SR-LIA 91 Output splitter 92 Output combiner 10 Antenna (Antenna 1, Antenna 2) 11 Laser 100 Method for determining an external magnetic field using an NV magnetometer with automatic resonance control 110 Resonance frequency f ± Recording a single resonance signal V for determining SR-LIA 120 Double resonance signal V having a dispersion form and a linear range around the resonance frequency f ± Recording DR-LIA 130 Determining the slope of the linear range as the scalar factor α from the demodulated signal V DR-LIA 140 Off-resonance Δ DR-LIA of the resonance frequency f via the demodulated signal V with resonance emission of microwave radiation ± B =V DR-LIA Observing / α 150 Using a controller including a control algorithm based on the observed off-resonance Δ B to control the microwave frequency f​​​​​MW To control 152 The demodulated signal V LIA To compare with the set value r = 0 154 The deviation e = r - V LIA=- V LIA To calculate 156 Using a controller, shift the frequency band of the microwave radiation in the opposite direction by Δf MW Only shift 160 To determine the external magnetic field B α Scalar factor γ Magnetic rotation ratio of the NV center B External magnetic field D(T,P) Energy level depending on pressure and temperature Δ B Detuning (resonance) caused by magnetic field change (magnetic detuning) Δ T Detuning (resonance) due to changes in pressure or temperature e The deviation e = r - V LIA=- V LIA f ± Spin state m s = 0 and m s = ±1 and the resonance frequency of the transition between f MW Microwave frequency f MW+ Resonance frequency f + The microwave frequency of the excitation of f MW- Resonance frequency f - The microwave frequency of the excitation of f SB Carrier frequency Δf MW Using a controller to shift the frequency band of the microwave radiation in the opposite direction FL Fluorescence L Output m s Spin state (0 = ground state, ±1: excited state) p Pressure r Set value of the controller S Output signal of the control system T Temperature Tc Control period V SR-LIA Single resonance signal V DR-LIA Demodulated signal

Claims

1. A method (100) for determining an external magnetic field using an NV magnetometer (1) having auto-resonance control, wherein the NV magnetometer (1) has respective spin states m ｓ = 0, m ｓ = ±1, and the resonance frequency f ｓ between the spin states m ｓ = 0 and m ± = ±1, and a sensor material (2) having an NV center having the resonance frequency f ± , and the difference f ＋ - f － of the resonance frequencies depends on the external magnetic field B, and the method (100) comprises Microwave frequency f ＭＷ and carrier frequency f ＳＢ In a frequency band based on, a single resonance signal V ± is recorded in step (110) for determining the resonance frequency f ＳＲ－ＬＩＡ by frequency-modulated microwave radiation emitted onto the sensor material (2), the microwave frequency f ＭＷ and the carrier frequency f ＳＢ being selected such that the frequency band addresses two magnetic resonances in succession, the recording step (110); The resonance frequency f ± A double resonance signal V having a dispersion form and a linear range around ＤＲ－ＬＩＡ Step (120) of recording, where f is such that both magnetic resonances are excited simultaneously ＭＷ ±f ＳＢ = f ± The microwave frequency f is adapted to ＭＷ And the carrier frequency f ＳＢ Is selected, step (120) of recording, and Demodulated signal V ＤＲ－ＬＩＡ a step (130) of determining the slope of the linear range as a scalar factor α from The evaluation unit (4) observes, via the demodulated signal V accompanied by the resonance emission of the microwave radiation due to the external magnetic field change, the detuning Δ ＤＲ－ＬＩＡ of the resonance frequency f ± by Δ Ｂ = V ＤＲ－ＬＩＡ / α in step (140); The observed detuning Δ Ｂ Using a controller (5) including a control algorithm based on the above, the frequency band f ＭＷ ±f ＳＢ is such that even after the detuning Δ Ｂ has occurred, this detuning Δ Ｂ the resonant frequency f of the NV centers present in this detuning Δ ± remains within the range, the frequency band f ＭＷ ±f ＳＢ Controlling step (150) to The distance 2*f between the two frequency bands by the evaluation unit (4) ＳＢ and the modulation deviation Δ Ｂ and a step (160) of determining the external magnetic field B therefrom, a method (100).

2. The step of controlling (150) is the demodulated signal V ＤＲ－ＶＩＡ a step (152) of comparing it with a set value r = 0, The deviation e = r - V ＤＲ－ＬＩＡ＝－ V ＤＲ－ＬＩＡ a step (154) of calculating Using the controller (5), shifting the frequency band of the microwave radiation in the opposite direction by Δf ＭＷ step (156), and the method (100) according to claim 1, comprising:

3. The controller (5) controls according to a rule Δf ＭＷ The method (100) according to claim 2, wherein the controller (5) is an integral software-based controller that controls according to [n]=K*(e[0]+e[1]+…+e[n]), K is the proportionality coefficient of the controller (5), and i = 0, 1, …, n are iteration steps.

4. The method (100) according to claim 3, wherein the proportionality coefficient K = 1 / α.

5. The controller (5) has a control cycle Tc, and after the control cycle Tc, the microwave frequency f ＭＷ is controlled again using the controller, and the control cycle Tc is from 1 μs to 10 s, preferably from 0.05 s to 1 s, more preferably 0.5 s, the method (100) according to any one of claims 1 to 4.

6. The signal generator (61) generates a signal having the microwave frequency f ＭＷ and a further signal generator (62) generates a frequency modulated signal having the carrier frequency f ＳＢ , the modulation frequency f ｍ , and the modulation amplitude f ｄ , where f ＳＢ (t) = f ＳＢ + f ｄ * cos(2πf ｍ t) and t is the time having each output, the method (100) according to any one of claims 1 to 5.

7. The two signals are frequency mixed by a frequency mixer (9), and the microwave radiation emitted onto the sensor material (2) has the two frequency bands f ＭＷ + f ＳＢ (t) and f ＭＷ − f ＳＢ (t), where f ＳＢ (t) is phase shifted by π in f ＭＷ − f ＳＢ (t). The method (100) according to claim 6

8. the microwave frequency f ＭＷ and the carrier frequency f ＳＢ are selected such that the two frequency bands each resonate with the resonance frequency f ± The method (100) according to claim 7, wherein

9. The method (100) according to any one of claims 6 to 8, wherein both frequency bands are emitted with individually adjusted outputs.

10. The method (100) according to claim 9, wherein the output is individually adjusted by a programmable attenuator (7) or by adjusting the output of the signal generator (61, 62).

11. An NV magnetometer (1) for determining an external magnetic field B, configured to execute the method (100) for automatic resonance control according to any one of claims 1 to 10, Each spin state m ｓ = 0, m ｓ = ±1, and the spin state m ｓ = 0 and m ｓ The resonance frequency f of the transition between ±1 ± And a sensor material (2) having an NV center having, the resonance frequency f ± The difference f of ＋ -f － Is dependent on the external magnetic field B, the sensor material (2), and Microwave frequency f ＭＷ and carrier frequency f ＳＢ in a frequency band based on the microwave frequency modulation microwave radiation emitted onto the sensor material (2), the resonance frequency f ± A microwave transmitter (6) for exciting magnetic resonance at, the microwave frequency f ＭＷ and the carrier frequency f ＳＢ are selected such that the frequency band addresses two magnetic resonances in succession, the microwave frequency f ＳＲ－ＬＩＡ and the carrier frequency f ＭＷ are selected to record a double resonance signal V ＳＢ such that both magnetic resonances are excited simultaneously, f ＭＷ ± f ＳＢ = f ± is adapted, a microwave transmitter (6) selected to record the double resonance signal V ＤＲ－ＬＩＡ and, A laser (11) for emitting in continuous wave mode having a wavelength in the range of 510 to 540 nm for continuous initialization and reading of the spin state, A suitable detector (8), preferably an optical detector, for recording frequency-modulated fluorescence from the sensor material (2), A lock-in amplifier (3) for demodulating the fluorescence, wherein one or both of the magnetic resonance excitations are signals V ± having a distributed form and a linear range around the resonance frequency f ＳＲ－ＬＩＡ or V ＤＲ－ＬＩＡ resulting in, the lock-in amplifier (3); the demodulated signal V ＤＲ－ＬＩＡ via which the resonance frequency f ± detuning Δ Ｂ = V ＤＲ－ＬＩＡ / α for observing by an evaluation unit (4); The observed detuning Δ Ｂ Using a control algorithm based on, the frequency band f ＭＷ ± f ＳＢ is such that even after the detuning Δ Ｂ has occurred, this detuning Δ Ｂ the resonance frequency f of the NV centers present in ± remains within the range of, the frequency band f ＭＷ ± f ＳＢ A controller (5) for controlling, and comprising The evaluation unit (4) is provided for determining the external magnetic field B from the distance 2*f of the two frequency bands ＳＢ and the deviation Δ Ｂ of an NV magnetometer (1).

12. The microwave transmitter (6) generates a signal having the microwave frequency f ＭＷ and a signal generator (61) for generating a signal having the carrier frequency f ＳＢ , a modulation frequency f ｍ , and a further signal generator (62) for generating a frequency modulation signal having a modulation amplitude f ｄ , and f ＳＢ (t) = f ＳＢ + f ｄ *cos(2πf ｍ t), where t is the time having each output, and the NV magnetometer (1) according to claim 11, characterized in that.

13. The NV magnetometer (1) according to claim 12, wherein the signal generator (61, 62) is configured to adjust the output of the signal, or the signal generator (61, 62) has an attenuator (7) connected upstream for individual output adjustment.

14. The NV magnetometer (1) according to any one of claims 11 to 13, wherein the sensor material (2) is diamond.

15. Use of one or more NV magnetometers according to any one of claims 11 to 14 for magnetic field gradient measurement.

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