NV color center magnetic detection or temperature measurement method based on zero field splitting coefficient

Abstract

The invention belongs to the technical field of quantum precision sensing, and particularly relates to an NV color center magnetic detection or temperature measurement method based on a zero field splitting coefficient, which is characterized in that a hypothetical magnetic field vector is calculated according to lattice structure characteristics of a diamond regular tetrahedron, and the zero field splitting coefficient is calculated according to the amplitude of the vector. Frequency deviation introduced by the transverse magnetic field is fully considered, and the accuracy is improved on the basis of the steps. Compared with an existing method, the calculated zero field splitting coefficient is more accurate, an error analysis method is provided, and magnetic field measurement or temperature measurement can be achieved through a more accurate D value by means of the method.

Description

Technical Field

[0001] The present invention belongs to the technical field of quantum precision sensing, and specifically relates to a method for NV color center magnetic detection or temperature measurement based on a zero-field splitting coefficient. Background Art

[0002] The nitrogen-vacancy color center in diamond is composed of a nitrogen atom that replaces a carbon atom and a nearby vacancy. This structure absorbs an electron from the surroundings to form a negatively charged NV. - structure, equivalent to a spin-1 electron, due to its 0 Color centers are more sensitive to magnetic fields and can be used in magnetic detection. In magnetic detection applications, negatively charged NV is abbreviated as NV. NV has a triplet ground state, m s = ±1 and m s = 0, due to the dipole-dipole interaction between electrons, m s = ±1 and m s =0 state degenerates. This phenomenon is not caused by the Zeeman splitting caused by the magnetic field. Therefore, it is distinguished as the zero-field splitting coefficient, abbreviated as ZFS, and represented by D in the Hamiltonian, D≈2.87GHz.

[0003] The NV color center structure has a symmetry axis, which is most sensitive to the parallel component of the magnetic field along the symmetry axis. To a certain extent, the two transition processes of the ground state spin-1 electron The transition frequency (f ± =D±γ e B) The difference Δf = f + -f - It is proportional to the size of the magnetic field projection, that is, the parallel component of the magnetic field contributes to the differential mode component of the transition frequency. However, the perpendicular component of the magnetic field relative to the symmetry axis still contributes to the transition frequency f ± Contributes, as shown in the transition frequency f ± Although it has little effect on the magnetic field projection result calculated by the difference Δf to a certain extent, it has a great influence on the magnetic field modulus value calculation formula and polar angle calculation formula obtained by Hamiltonian analysis, because the common mode component caused by the transverse magnetic field will interfere with the measurement of the zero-field splitting coefficient.

[0004] On the other hand, existing research has found that the zero-field splitting coefficient is temperature dependent, dD / dT≈-74kHz / K. Based on this property, NV color centers can also be used in the field of temperature sensors. ± The common mode component, f ± =D+(dD / dT)*T±γ eB. In the NV color center magnetic detection based on the optical detection magnetic resonance method, the necessary microwave antenna will heat the diamond sample, causing the ambient temperature to change continuously, which causes D to shift from the initial value of 2.87GHz in the absence of a magnetic field. Magnetic fields of different directions and amplitudes introduce different transverse magnetic fields, further shifting the transition frequency, making the measurement of D more difficult.

[0005] The existing zero-field splitting coefficient measurement method focuses more on dD / dT and does not require a high accuracy of D. The usual method is to measure the fluorescence spectrum of the NV color center to the microwave frequency of the frequency scan under the geomagnetic field by the optical detection magnetic resonance method, and obtain the fitted transition frequency f by fitting the spectrum. ± A simple way to calculate the zero-field splitting coefficient is to take the average of the two transition frequencies, D fit =(f + +f - ) / 2, D can also be fitted by analytical Hamiltonian fit In this method, on the one hand, since the exact value of the zero-field splitting coefficient is not taken into account, the transition frequency offset caused by the initial temperature and the geomagnetic field is ignored; on the other hand, even if this method no longer uses the geomagnetic field but applies a strong magnetic field to improve the fitting accuracy of the transition frequency, the vertical component of the vector magnetic field on the NV color center in various directions will also cause different degrees of common-mode displacement, increasing the difficulty of fitting and even giving multiple results. Therefore, this method cannot give an accurate zero-field splitting coefficient value, and the error introduced in the vector magnetic field detection is too large to be tolerated.

[0006] Another method is to use the temperature-dependent Debye-Waller coefficient (DWF), which is obtained by measuring the high-resolution spectrum at the zero-phonon line of the NV color center. The temperature obtained by this method can be used to calculate the accurate value of the zero-field splitting coefficient by the calibrated dD / dT mentioned above. However, on the one hand, the measurement mechanism of this method is not compatible with magnetic detection, and the two cannot usually be performed at the same time; on the other hand, this method requires fitting the zero-phonon line, and the fitting function consists of two Lorentz line shapes and a linear function. The fitting parameter setting of multiple functions may cause instability of the DWF and is relatively time-consuming.

[0007] It can be seen that at room temperature, the zero-field splitting coefficient D is 2.87 GHz, but under the influence of magnetic field and temperature, the actual value of D will be offset. The current method cannot accurately obtain the actual value of D after the offset, which affects the accuracy of NV color center magnetic detection or temperature measurement. Summary of the invention

[0008] In order to solve the above technical problems, the present invention provides a method for NV color center magnetic detection or temperature measurement based on the zero-field splitting coefficient. During the magnetic detection or temperature measurement process, the D value can be calculated in real time and accurately, and more reliable results can be given in the calculation of the magnetic field modulus and direction, which helps to improve the accuracy of magnetic detection or temperature measurement. The method of the present invention can be used for magnetic detection and temperature measurement at the same time and has good compatibility.

[0009] The present invention is specifically achieved through the following technical solutions.

[0010] The present invention provides a method for NV color center magnetic detection or temperature measurement based on a zero-field splitting coefficient. When the NV color center is used for magnetic detection, the zero-field splitting coefficient measurement method comprises the following steps:

[0011] S1. Place the diamond in the magnetic field to be tested to obtain the diamond ODMR spectrum (optical detection magnetic resonance spectrum). Read the first transition frequency and the second transition frequency on the ODMR spectrum, which are the microwave frequencies corresponding to the peak position in the ODMR spectrum, respectively. +,i and f -,i , where f +,i and f -,i is a pair of transition frequencies, i=1, 2, 3, 4, i is the type of NV color centers with four orientations existing in the diamond sample.

[0012] S2. Take the value of the room temperature zero-field splitting coefficient 2.87 GHz as the initial value of the zero-field splitting coefficient D ini , through D ini and the transition frequency f read from S1 +,i and f -,i Get the initial calculated angle θ ini,i , 4 initial calculation angles θ ini,i Composed of 1×4 angle vectors [θ ini ]; It should be noted that [θ ini ]All are acute angles, not the true angles between the magnetic field and the NV axis (the angle between vectors may be acute or obtuse), and do not include the positive or negative sign of the projection of the magnetic field on the NV axis.

[0013] θ ini,i The specific formula is as follows:

[0014]

[0015] In the above formula, D ini is 2.87 GHz, and E is the off-diagonal electric field / stress splitting energy.

[0016] S3, obtained from S2 [θ ini ], and obtain the minimum value Δ θ.min , using Δθ.min Verify the read f +,i and f -,i Is it correct.

[0017] Specifically through the minimum value formula: [Δ θ,min j Δ ]=min(|[cosθ ini ][p Δ ]|), and obtain the minimum value Δ θ.min ; Among them, [Δ θ，min j Δ ] represents the angle discriminant that satisfies the lattice structure constraint, j Δ Indicates the minimum value Δ θ.min The number of columns, When the minimum value Δ θ.min When it deviates from 0, it means f +,i and f -,i The reading is wrong. This is a problem with the experiment. Reread f +,i and f -,i ; until Δ θ.min = 0, get the correct f +,i and f -,i .

[0018] In addition, according to the minimum value formula, the minimum value Δ can also be calculated. θ.min [p Δ ] Δ Column [p], this column represents the positive and negative sign of the projection of the magnetic field on the NV axis. After obtaining [p], we can calculate the positive and negative sign of the magnetic field according to p. i The sign of θ is modified by mi,i , get the direction polar angle θ B,i , θ B,i It is the true angle between the magnetic field vector and the NV axis vector.

[0019] S4, the symbol vector [p] obtained by S3, and the verified f +,i And the verified f -,i Obtain magnetic field projection [B p ], using the NV color center ensemble model to reconstruct the vector direction of the magnetic field in the relative coordinate system based on a selected axis orientation, based on the magnetic field projection [B p ] and the relative coordinate system, construct the initial vector of the magnetic field

[0020] The specific formula is:

[0021]

[0022] Among them, the symbol vector [p] takes [p Δ ]Δ Column; θ NV =109.47°.

[0023] S5, after S3 verification, f +,i And the verified f -,i and S4 obtained Substitute the following formula to obtain the reference value D of the zero-field splitting coefficient: ref :

[0024]

[0025] S6, D ref Substitute the following formula to obtain the angle reference value θ ref , and obtain the angle reference value vector [θ ref ]:

[0026]

[0027] E is the off-diagonal electric field / stress splitting energy.

[0028] [θ ref ] is substituted into the following formula to obtain the error δD between the reference value of the zero-field splitting coefficient and the true value of the zero-field splitting coefficient:

[0029] Correcting D by δD ref , and obtain a result D close to the true value of the zero-field splitting coefficient D res .

[0030] S7, use S6 to get D res Conduct NV color center magnetic detection or temperature measurement.

[0031] Preferably, the ODMR spectrum is obtained using the following system:

[0032] The system comprises a diamond NV color center sample, an optical path system, a microwave generating device, a magnetic field generating device and a digital control system.

[0033] The optical path system comprises a laser generator, which is used for emitting laser light. An acousto-optic modulator and a beam splitter are sequentially arranged along the laser emission direction. After the laser light passes through the acousto-optic modulator and the beam splitter, it is split into laser light in a first direction and laser light in a second direction. A low-pass dichroic mirror and a first lens are sequentially arranged along the first direction. The first lens is arranged close to the diamond NV color center sample. A third lens and a second photodetector are sequentially arranged along the second direction. The laser light in the first direction passes through the low-pass dichroic mirror and is focused on the diamond NV color center sample by the first lens. The photoluminescence of the diamond NV color center sample is collected by the first lens and reflected by the low-pass dichroic mirror. A high-pass filter, a second lens and a first photodetector are sequentially arranged along the reflection direction. The reflected light is filtered and split by the high-pass filter and finally focused on the first photodetector by the second lens. The laser light in the second direction is focused on the second photodetector through the third lens.

[0034] The microwave generating device includes a microwave generator and a microwave antenna. The microwave antenna is placed close to the diamond NV color center sample. The microwave generator is used to output microwaves, and the microwave antenna is used to transmit microwaves to the diamond NV color center sample.

[0035] The magnetic field generating device includes a set of Helmholtz coils or an electromagnet and a matching current source, and the diamond NV color center sample is placed in the uniform field area in the center of the coil or electromagnet.

[0036] The digital control system consists of a voltage acquisition system, a PID controller, a signal generator and a host computer, wherein the voltage acquisition system is used to collect output signals of a first photodetector of the photodetector and the signal generator, the PID controller is used to negatively feedback control the acousto-optic modulator to stabilize the light intensity according to the laser light intensity measured by the second photodetector, and the signal generator is used to provide a reference signal for the frequency scanning of the microwave generator, and the reference signal and the photoelectric signal of the first photodetector of the photodetector are sent to the host computer for processing together, and finally the ODMR spectrum line is obtained.

[0037] Preferably, the mode of the microwave generator is set to a frequency scanning function, with 2870 MHz as the center frequency and a scanning depth of 200 MHz.

[0038] Preferably, the reference value of the zero field splitting coefficient is corrected with an error until ∑cos2θ ref When +4 / 3=0, the zero field splitting coefficient D close to the true value is obtained. res ,θ ref is the angle reference value.

[0039] Preferably, when the NV color center is used as a temperature sensor, the magnetic field to be measured in S1 is replaced by a calibrated standard magnetic field applied to the NV color center sample by a magnetic field generating device, and the magnetic field in the NV color center sensing area is uniform. At this time, the calculation formula is as follows: Wherein, B is the standard magnetic field modulus value.

[0040] Preferably, when the NV color center is used as a temperature sensor, the f read out in S3 is verified +,i and f -,i Is the correct step to replace: Using the minimum formula [Δ θ,min j Δ ]=min(|[cosθ ini ][p Δ ]|), and obtain the minimum value Δ θ.min ; Among them, [Δ θ，min j Δ ] represents the angle discriminant that satisfies the lattice structure constraint, j Δ Indicates the minimum value Δ θ.min The number of columns, When the minimum value Δ θ.min If the frequency deviates from 0, it means that the first transition frequency and the second transition frequency are not read correctly. Return to S1 to read the first transition frequency and the second transition frequency until Δ θ.min = 0, and the correct first transition frequency and second transition frequency are obtained. When the NV color center is used as a temperature sensor for temperature measurement, the zero field splitting coefficient at different temperatures is measured according to a standard temperature source to obtain the dD / dT relationship, and the zero field splitting coefficient close to the true value is substituted into the relationship to obtain the temperature value.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] The present invention proposes a method for NV color center magnetic detection or temperature measurement based on zero field splitting coefficient. First, the zero field splitting coefficient is measured by limiting the diamond lattice structure, and then the zero field splitting coefficient is used for magnetic detection or temperature measurement. The present invention can accurately calculate the D value in real time during the magnetic detection or temperature measurement process, and provide more reliable results in the calculation of magnetic field modulus and direction, which is helpful to improve the accuracy of magnetic detection or temperature measurement. Specifically:

[0043] The present invention first obtains the diamond ODMR spectrum line and reads the transition frequency f on the ODMR spectrum line. +,i and f -,i, taking the value of the room temperature zero-field splitting coefficient of 2.87GHz as the initial value (imaginary value) of the zero-field splitting coefficient, the initial vector of the magnetic field is obtained by calculation. The key of the present invention is to infer the imaginary magnetic field vector according to the characteristics of the diamond tetrahedron lattice structure, and realize the measurement of the zero-field splitting coefficient by the modulus value of the vector. The effect is that the created imaginary magnetic field vector is only affected by the readout error of the first transition frequency and the second transition frequency, and the influencing factor comes from the system error. The calculated zero-field splitting coefficient is more reliable, has a unique solution, and the unique solution has high stability. Compared with the first method in the background technology, that is, the resonance frequency averaging method, the problem of multiple solutions of the non-unique resonance frequency average value under a strong magnetic field is solved.

[0044] The key to the present invention is to comprehensively analyze and quantify the influence of the error between the reference value of the zero-field splitting coefficient and the true value of the zero-field splitting coefficient on the angle reference value obtained by reading the frequency calculation, so that the frequency offset introduced by the transverse magnetic field is fully considered, and the accuracy is further improved. Compared with the existing method, the measured zero-field splitting coefficient is more accurate, and an error analysis method is provided.

[0045] Through the above content of the present invention, the zero-field splitting coefficient can be used more accurately to realize the measurement of magnetic field or temperature. In the zero-field splitting coefficient measurement method applied to magnetic detection, the measured magnetic field provides a magnetic field environment, but the zero-field splitting coefficient value is required to measure the measured magnetic field, so the zero-field splitting coefficient value is calculated by reading the ODMR spectrum line and transition frequency under the measured magnetic field, and a more accurate magnetic field amplitude and magnetic field angle are obtained. In the zero-field splitting coefficient value measurement method applied to temperature measurement, since there is no measured magnetic field, it is necessary to artificially apply a magnetic field, so the amplitude of this magnetic field is known. Through the value of dD / dT, the more accurate the measured zero-field splitting coefficient value is, the more accurate the measured temperature is. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 A schematic diagram of the system structure used for obtaining diamond ODMR spectrum lines in the present invention.

[0047] Figure 2 In the figure, (a) is the NV color center axis orientation model, and (b) is the schematic diagram of the ODMR spectrum line.

[0048] Figure 3 In the figure, (a) is the error function judgment standard, and (b) is the flowchart diagram. DETAILED DESCRIPTION

[0049] In order to enable those skilled in the art to better understand and implement the technical solution of the present invention, the present invention is further described below in conjunction with specific embodiments and drawings, but the embodiments are not intended to limit the present invention.

[0050] Explanation of symbols:

[0051] D: Zero field splitting coefficient.

[0052] D ref : Reference value of zero-field splitting coefficient.

[0053] D res : Zero-field splitting coefficient close to the true value.

[0054] i: orientation of NV color center in diamond sample, i=1,2,3,4.

[0055] f +,i and f -,i : The first transition frequency and the second transition frequency.

[0056] [f ± ]:A 2×4 matrix consisting of 4 pairs of f_+,i and f_-,i.

[0057] |B i |: Magnetic field modulus, used to calculate D value.

[0058] θ B : The angle between the magnetic field vector and the NV axis vector.

[0059] [θ B ]: A 1×4 angle vector composed of the angles between the magnetic field vector and the NV axis vectors of four orientations.

[0060] θ B,i : Direction polar angle, the angle between the magnetic field vector and each NV axis vector.

[0061] θ ini,i : Initial calculation angle.

[0062] [θ ini ]: 1×4 angle vector consisting of the 4 initial calculated angles.

[0063] [p]: Sign vector, a 4×1 column vector composed of the positive and negative signs of the projection of the magnetic field vector on the NV axis vector of four orientations. It reflects whether the angle between the magnetic field vector and the NV axis is acute or obtuse.

[0064] [p Δ ]: A symbolic matrix used for testing. It has no special meaning and the symbolic vector is one of its columns.

[0065] θ ref : Angle reference value.

[0066] [θ ref ]: Angle reference value vector.

[0067] The zero-field splitting coefficient is generated by the dipole-dipole interaction in the diamond lattice containing nitrogen-vacancy (NV) color centers. It is usually abbreviated as D in the Hamiltonian. It makes the ground state spin state of the NV color center degenerate and is used as a constant in most studies. In recent studies on the temperature dependence and vector magnetic detection of NV color centers, it was found that the zero-field splitting coefficient is a physical quantity that changes with temperature and participates in the calculation of the magnetic field modulus and magnetic field direction in magnetic field detection. Therefore, the measurement or pre-calculation of the zero-field splitting coefficient is crucial for vector and scalar magnetic detection based on NV color centers. Most existing studies focus on calibrating the sensitivity of the zero-field splitting coefficient to temperature T, that is, dD / dT, but lack attention to the accurate value of ZFS. The D value measured by the existing method usually produces large errors when calculating the magnetic field modulus and angle. The present invention proposes a method for measuring zero-field splitting energy limited by a diamond lattice structure, which can accurately calculate the D value in real time during magnetic detection or temperature measurement, and provide more reliable results in the calculation of magnetic field modulus and direction, which helps to improve the accuracy of magnetic detection or temperature measurement, and the method of the present invention can be used in magnetic detection and temperature measurement at the same time, and has good compatibility. The method provided by the present invention comprises the following steps:

[0068] S1. Place the diamond in a magnetic field and obtain the diamond ODMR spectrum line, and read the first transition frequency f on the ODMR spectrum line. +,i and the second transition frequency f -,i , where f +,i and f -,i is a pair of transition frequencies, i = 1, 2, 3, 4, i is the orientation of the NV color center in the diamond sample.

[0069] S2, take 2.87GHz as the initial value of zero field splitting coefficient D ini , through D ini and f read from S1 +,i and f -,i Get the initial calculated angle θ ini,i , 4 initial calculation angles θ ini,i Composed of 1×4 angle vectors [θ ini ].

[0070] S3, obtained from S2 [θ ini ], and obtain the minimum value Δ through the minimum value calculation formula θ.min and the minimum value Δ θ.min The corresponding symbol vector [p], using Δ θ.min Verify the f read by S1 +,i and f -,i Is it correct.

[0071] S4, symbol vector [p] obtained using S3, f after verification by S3+,i And after verification f -,i Obtain magnetic field projection [B p ], using the NV color center ensemble model to reconstruct the vector direction of the magnetic field in the relative coordinate system based on a selected axis orientation, based on the magnetic field projection [B p ] and the relative coordinate system, construct the initial vector of the magnetic field And get the initial vector of the magnetic field The modulus value of .

[0072] S5, using the modulus of the initial vector of the magnetic field, f after verification in S3 +,i And after verification f -,i Obtain the reference value D of the zero-field splitting coefficient ref .

[0073] S6. Use D ref 、After verification +,i And after verification f -,i Get the angle reference value [θ ref ], using [θ ref ]Get D ref The error δD between the true value of the zero-field splitting coefficient D is used to correct D ref , and obtain the zero-field splitting coefficient D close to the true value res .

[0074] S7, use S6 to get D res Conduct NV color center magnetic detection or temperature measurement.

[0075] The present invention is specifically described in the following content.

[0076] like Figure 1As shown, the experimental system of the present invention is composed of a diamond NV color center sample 13, an optical path system, a microwave generator, a magnetic field generator and a digital control system. The optical path system includes a 532nm laser generator 1. The laser passes through the acousto-optic modulator 2 and the beam splitter 3 and is focused on the diamond NV color center sample 13 by the first lens 14. The photoluminescence of the diamond NV color center sample 13 is collected by the first lens 14, filtered and split by the low-pass dichroic mirror 4 and the high-pass filter 6, and finally focused on the first photodetector 16 by the second lens 7. Another part of the laser is focused on the second photodetector 17 through the third lens 5. The microwave generator includes a microwave generator 11 with a microwave frequency band of 2GHz-4GHz and a microwave antenna 12. The microwave antenna 12 is placed close to the diamond NV color center sample 13. The mode of the microwave generator 11 is set to the frequency scanning function, with 2870MHz as the center frequency and the scanning depth of about 200MHz. The magnetic field generating device includes a set of Helmholtz coils 15 or an electromagnet, and a matching current source 10, wherein the diamond NV color center sample 13 should be placed in the uniform field area in the center of the Helmholtz coil 15 or the electromagnet. The digital control system consists of a voltage acquisition system, a PID controller, a signal generator 9 and a host computer 8, wherein the voltage acquisition system is used to collect the output signals of the first photodetector 16 and the signal generator 9, the PID controller is used to negatively feedback control the acousto-optic modulator 2 to stabilize the light intensity according to the laser light intensity measured by the second photodetector 17, and the signal generator 9 is used to provide a reference signal for the frequency scanning of the microwave generator 11, which is sent to the host computer 8 together with the photoelectric signal of the first photodetector 16 for processing, and finally the following is obtained: Figure 2 The ODMR spectrum shown in the figure below. Limited by the diamond tetrahedral lattice structure, there are four types of NV color centers in the diamond sample, and the angle between the symmetry axes is 109.47°. When the vector magnetic field interacts with the four types of NV color centers in a certain direction, its magnetic field projection on the four symmetry axes will produce four pairs of transition frequencies f ±,i (i.e. f +,i and f -,i ), i=1,2,3,4, corresponding to Figure 2 The microwave frequencies corresponding to the four pairs of peaks in the ODMR spectrum shown in the middle and lower figures. By analyzing the ground state energy level Hamiltonian of the NV color center, the magnetic field modulus |B i |、The angle θ between the magnetic field vector and the NV axis vector B With each pair of transition frequencies f ±,i The relationship between them is:

[0077]

[0078] Where E is the off-diagonal electric field / stress splitting energy, which is a known constant in the present invention and is usually much smaller than D, γ e =28GHz / T is the NV color center gyromagnetic ratio. It can be seen from formula (1) and formula (2) that D directly affects the magnetic field calculation results in the scalar magnetic sensing and vector magnetic sensing processes, and the weight of D is more obvious when calculating the magnetic field angle. Therefore, when using NV color centers for magnetic detection, in order to measure the measured magnetic field, it is necessary to obtain the D value.

[0079] Although we do not know the absolute directions of the four orientations of the NV color center axis in the laboratory frame, due to the symmetry of the crystal, we can use the following NV color center ensemble model to reconstruct the vector direction of the magnetic field in the relative coordinate system based on a selected axis orientation, such as Figure 2 shown.

[0080]

[0081] Row vectors are expressed as unit vectors with four axis orientations. For ease of calculation, the base vector Parallel to the z-axis.

[0082] Since the magnetic field modulus is unknown during magnetic detection, formula (1) is not applicable to give the exact value of D. At the same time, the preset zero-field splitting coefficient initial value D is substituted into formula (2): ini (2.87 GHz) often gives unstable angle calculation results, which are not of reference value, so other methods are needed to mathematically express the constraints on the D value. ± The calculated magnetic field projection can give the modulus of the magnetic field without the participation of D, which can be used to give the reference value of the iterative algorithm of D. ± What is actually calculated is the absolute value of the magnetic field projection, that is, the response of the NV color center to a pair of magnetic field vectors in opposite directions is consistent, only the transition frequency is exchanged. We first need to solve the problem of how to obtain the sign of the magnetic field projection. This corresponds to how to determine the 1×4 angle vector [θ B ] is an acute angle or an obtuse angle. Due to the characteristics of the double angle, formula (2) can only calculate the initial calculation angle θ of the magnetic field polar angle. ini,i ∈(0,π / 2) acute angle, so in the calculation, we have to calculate the polar angle θ for each direction B,i Consider θ ini,i and π-θ ini,i The two results correspond to the positive and negative signs of the projection of the magnetic field on the NV axis.

[0083] The angle between the vector magnetic field and the axis orientation should satisfy the NV color axis angle θ constrained by the diamond tetrahedral lattice structure. NV =109.47°, that is:

[0084]

[0085] According to [θ B ] and [θ ini ], modify formula (4) as the discriminant condition of the symbol vector [p],

[0086]

[0087] where p i =1 or -1 indicates the positive or negative sign of the magnetic field projection on the NV axis, as well as the direction angle θ B,i With the initial calculated angle θ ini,i The relationship between:

[0088]

[0089] When reading out the 4 groups of transition frequencies [f ± ], with the initial value of zero field splitting coefficient D ini Calculate the initial angle matrix [θ ini ], considering the readout error of the transition frequency and the initial value of the zero-field splitting coefficient D ini The error between the true value and the true value, formula (5) can be expanded to

[0090] [Δ θ,min j Δ ]=min([cosθ ini ][p Δ ]) (7)

[0091] in

[0092]

[0093] j Δ Indicates the minimum value Δ θ.min The number of columns, symbol vector [p] takes [p Δ ] Δ Although the calculation of the symbol matrix requires the preset D ini Participate, but the sign vector [p] given by the angle relationship is more stable and has an initial value D for the zero-field splitting coefficient ini The dependence of is weak, so D is not introduced when calculating the magnetic field modulus. ini of error.

[0094] Substitute the symbol vector [p] into the calculated magnetic field projection [B p ]:

[0095]

[0096] The initial vector of the magnetic field can be constructed based on the relative coordinate system defined by formula (3):

[0097]

[0098] Among them [B p The absolute value of the transition frequency [f ± ] is given, θ NV Determined by the diamond lattice structure, only [B p ] and D ini Although the D value changes in a large range will give an unstable [θ B ], but due to the generous judgment conditions in formula (7), it can still maintain a stable [p], so For the preset D ini The dependence is weak, which ensures good robustness. Substituting the modulus value of the initial magnetic field vector into formula (1) can calculate the iterative D value:

[0099]

[0100] Considering the readout error of the transition frequency, there may be some deviations in the D values ​​calculated for the 4 pairs of transition frequencies, so the average of the calculated results is taken as a reference value.

[0101] So far, we have set the reference value D ref Anchored near the true value of D, but if you want to get the D value more accurately, the calculation accuracy of formula (9) can no longer guarantee the accuracy. The subsequent calculation will be based on the angle [θ ref ]. By reference value D ref Calculated [θ ref ] gives the relative direction of the vector magnetic field in the relative coordinate system defined by formula (5):

[0102]

[0103] in,

[0104]

[0105]

[0106] Determined by the magnitude of the unit vector created, [θ ref ] Another condition still needs to be met, namely:

[0107]

[0108] The error in the equation comes from [θ ref ], that is, D substituted into formula (2) ref The error δD between the true value of D and D is consideredref =D+δD Substituting into formula (2), we obtain formula (15) with error, namely:

[0109]

[0110] Since the reference value D ref It is already near the true value of D, so δD<<D, which can be roughly considered as ∑cos2θ ref ∝δD, and when δD=0, ∑cos2θ ref = -4 / 3, so we can ref A small change δD is added to find D. For ease of calculation, the error function is set to:

[0111]

[0112] Error function changes with δD Figure 3 , when D is taken as the reference quantity, Err(δD=0)=0; when the reference quantity D with error is taken as the reference quantity ref When it is a reference quantity, for example, D ref >D, then Err(δD<0)=0, and D is corrected by δD ref To get a result closer to D res .

[0113] When the NV color center is used as a temperature sensor for temperature measurement, since there is no magnetic field to be measured, a magnetic field needs to be artificially applied. Specifically, a calibrated standard magnetic field can be applied to the NV color center through a magnetic field generating device. Since the sensing area of ​​the NV color center is usually in the micrometer to millimeter size, and the uniform area of ​​the magnetic field generating device such as coils and magnets is often much larger than this size, it can be considered that the magnetic field in the sensing area of ​​the NV color center is uniform. Therefore, in formula (1), |B i | should be consistent, and the D value can be calculated based on the known standard magnetic field modulus value:

[0114]

[0115] In addition, the angle calculation formula in formula (2) can be used to verify D ref If the calculated D value does not satisfy formula (5), the transition frequency f ± There is a large error in the reading, or there is a magnetic material in the measurement system that makes the standard magnetic field amplitude inaccurate. This can be verified by the subsequent steps. ref Correctness of value.

[0116] The D value at different temperatures T is measured according to a standard temperature source to obtain dD / dT. Therefore, the temperature T value can be obtained from the D value calculated according to the method of the present invention, and the more accurate the D value is, the more accurate the measured T value is.

[0117] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, they are also intended to be included.

Claims

1. A method for NV color center magnetic detection or temperature measurement based on zero field splitting coefficient, characterized in that: The following steps are involved: Placing the diamond in a magnetic field and obtaining a diamond ODMR spectrum line, and reading a first transition frequency and a second transition frequency on the ODMR spectrum line, wherein the first transition frequency and the second transition frequency are a pair of transition frequencies, which are microwave frequencies corresponding to the position of a peak in the ODMR spectrum line; The value of the zero-field splitting coefficient at room temperature is used as the initial value of the zero-field splitting coefficient, and the initial calculation angle is obtained through the initial value of the zero-field splitting coefficient and the read first transition frequency and second transition frequency, and the initial calculation angle constitutes an angle vector; Obtain a minimum value and a sign vector corresponding to the minimum value from the obtained angle vector by using a minimum value calculation formula, and use the minimum value to verify whether the read first transition frequency and second transition frequency are correct; Obtaining a magnetic field projection using the symbol vector, the verified first transition frequency, and the verified second transition frequency, constructing an initial vector of the magnetic field, and obtaining a modulus value of the initial vector of the magnetic field; Obtaining a reference value of a zero-field splitting coefficient using a modulus value of an initial vector of a magnetic field, a verified first transition frequency, and a verified second transition frequency; Obtain an angle reference value using a reference value of the zero-field splitting coefficient, a verified first transition frequency, and a verified second transition frequency, obtain an error between a reference value of the zero-field splitting coefficient and a true value of the zero-field splitting coefficient using the angle reference value, and correct the reference value of the zero-field splitting coefficient using the error to obtain a zero-field splitting coefficient close to the true value; Use zero-field splitting coefficients close to their true values ​​for NV color center magnetic detection or temperature measurement.

2. The method according to claim 1, characterized in that The ODMR spectrum is obtained using the following system: The system comprises a diamond NV color center sample (13), an optical path system, a microwave generating device, a magnetic field generating device and a digital control system; The optical path system comprises a laser generator (1), the laser generator is used to emit laser light, an acousto-optic modulator (2) and a beam splitter (3) are sequentially arranged along the laser emission direction, and the laser light is split into laser light in a first direction and laser light in a second direction after passing through the acousto-optic modulator (2) and the beam splitter (3); along the first direction, a low-pass dichroic mirror (4) and a first lens (14) are sequentially arranged, the first lens (14) is arranged close to the diamond NV color center sample (13), and along the second direction, a third lens (5) and a second photodetector (17) are sequentially arranged, and the laser light in the first direction passes through the acousto-optic modulator (2) and the beam splitter (3). The low-pass dichroic mirror (4) is focused on the diamond NV color center sample (13) by the first lens (14); the photofluorescence of the diamond NV color center sample (13) is collected by the first lens (14) and reflected by the low-pass dichroic mirror (4); along the reflection direction, a high-pass filter (6), a second lens (7) and a first photodetector (16) are sequentially arranged; the reflected light is filtered and split by the high-pass filter (6) and finally focused on the first photodetector (16) by the second lens (7); the laser light in the second direction is focused on the second photodetector (17) by the third lens (5); The microwave generating device comprises a microwave generator (11) and a microwave antenna (12), wherein the microwave antenna (12) is placed close to the diamond NV color center sample (13); the microwave generator (11) is used to output microwaves, and the microwave antenna (12) is used to transmit microwaves to the diamond NV color center sample (13); The magnetic field generating device comprises a set of Helmholtz coils (15) or an electromagnet and a matching current source (10), and the diamond NV color center sample (13) is placed in the uniform field area at the center of the Helmholtz coil (15) or the electromagnet; The digital control system comprises a voltage acquisition system, a PID controller, a signal generator (9) and a host computer (8), wherein the voltage acquisition system is used to acquire output signals of a first photodetector (16) and the signal generator (9), the PID controller is used to negatively feedback control the acousto-optic modulator (2) to stabilize the light intensity according to the laser light intensity measured by the second photodetector (17), and the signal generator (9) is used to provide a reference signal for the frequency scanning of the microwave generator (11), and the reference signal and the photoelectric signal of the first photodetector (16) are sent to the host computer (8) for processing, and finally the ODMR spectrum line is obtained.

3. The method according to claim 2, characterized in that The mode of the microwave generator (11) is set to a frequency scanning function, with 2870 MHz as the center frequency and a scanning depth of 200 MHz.

4. The method according to claim 1, characterized in that: When NV color centers are used for magnetic detection, the magnetic field is the magnetic field to be measured.

5. The method according to claim 4, characterized in that When the NV color center is used for magnetic detection, the steps to verify whether the read first transition frequency and second transition frequency are correct are: using the minimum formula [Δ θ,min j Δ ]=min(|[cosθ ini ][p Δ ]|), and obtain the minimum value; where Δ θ.min Indicates the minimum value, [Δ θ，min j Δ ] represents the angle discriminant that satisfies the lattice structure constraint, j Δ Indicates the number of columns with the minimum value. When the minimum value deviates from 0, it indicates that the first transition frequency and the second transition frequency are read incorrectly, and the first transition frequency and the second transition frequency are read again until the minimum value is 0, thereby obtaining the correct first transition frequency and the second transition frequency.

6. The method according to claim 2, characterized in that When the NV color center is used as a temperature sensor for temperature measurement, the magnetic field is: a calibrated standard magnetic field is applied to the diamond NV color center sample through the magnetic field generating device, and the magnetic field in the sensing area of ​​the diamond NV color center sample is uniform. At this time, the modulus of the initial vector of the magnetic field is the modulus of the standard magnetic field.

7. The method according to claim 6, characterized in that When the NV color center is used as a temperature sensor, the steps to verify whether the read first transition frequency and second transition frequency are correct are: using the minimum value formula [Δ θ,min j Δ ]=min(|[cosθ ini ][p Δ ]|), and obtain the minimum value; where Δ θ.min is the minimum value, [Δ θ，min j Δ ] represents the angle discriminant that satisfies the lattice structure constraint, j Δ Indicates the minimum value Δ θ.min The number of columns, When the minimum value deviates from 0, it indicates that the first transition frequency and the second transition frequency are read incorrectly, and the first transition frequency and the second transition frequency are read again until the minimum value is 0, thereby obtaining the correct first transition frequency and the second transition frequency.

8. The method according to claim 1, characterized in that: The reference value of the zero-field splitting coefficient is corrected by the error until φcos2θ ref When +4 / 3=0, the zero-field splitting coefficient close to the true value is obtained, θ ref is the angle reference value.

9. The method according to claim 1, characterized in that: The NV color center is used as a temperature sensor for temperature measurement. The zero-field splitting coefficient D is measured at different temperatures T according to a standard temperature source to obtain the dD / dT relationship. The zero-field splitting coefficient close to the true value is substituted into the relationship to obtain the temperature value.

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