A method and system for improving the accuracy of diamond NV color core current measurement

Abstract

This invention relates to the field of current measurement technology and discloses a method and system for improving the accuracy of NV center current measurement in diamond. The method includes: applying an axial magnetic field outside the diamond sample; comparing the energy level difference between two characteristic states with the target spin; determining whether energy level anti-crossing exists based on the comparison result; determining the fluorescence intensity based on the energy level anti-crossing; determining a normalized fluorescence signal based on the initial fluorescence signal and the target fluorescence signal; determining the coupling relationship between the magnetic field and fluorescence intensity based on the fluorescence intensity, the normalized fluorescence signal, and the placement probability; applying a bias magnetic field opposite to the axial magnetic field based on the open-loop transfer function and the microwave frequency; modulating the measurement microwave frequency with a sine wave; and measuring the NV center current based on the Fourier coefficients, the adjusted signal-to-noise ratio, and the bias magnetic field. This invention improves the accuracy of current measurement.

Description

Technical Field

[0001] This invention relates to the field of current measurement technology, and more specifically, to a method and system for improving the accuracy of diamond NV color center current measurement. Background Technology

[0002] Nitrogen-vacancy (NV) centers in diamond, as a solid-state quantum system, have become important research objects in quantum precision measurement, quantum information processing, and biomedical imaging due to their excellent optical stability at room temperature, long spin decoherence time, high spatial resolution, and high sensitivity to physical quantities such as electric fields, magnetic fields, and temperature. In the field of current measurement, current sensing technology based on diamond NV centers can achieve non-contact and precise detection of weak currents at the micro-nano scale. However, in practical applications, the background magnetic field in the measurement environment can cause non-target modulation of the spin state and fluorescence signal of the NV center, resulting in a decrease in the signal-to-noise ratio. Furthermore, traditional demodulation algorithms are difficult to effectively suppress noise and signal distortion, making it difficult for NV center current measurement to meet the requirements of high-precision measurement.

[0003] Therefore, it is necessary to design a method and system to improve the accuracy of diamond NV color center current measurement in order to solve the problems existing in the current technology. Summary of the Invention

[0004] In view of this, the present invention proposes a method and system for improving the accuracy of diamond NV center current measurement, aiming to solve the problem that the background magnetic field in the measurement environment will cause non-target modulation of the spin state of the NV center and the fluorescence signal, resulting in a decrease in the signal-to-noise ratio of the signal, and the demodulation algorithm is difficult to effectively suppress noise and signal distortion, making it difficult for the NV center current measurement to meet the requirements of high-precision measurement.

[0005] In one aspect, the present invention proposes a method for improving the accuracy of diamond NV color center current measurement, comprising:

[0006] An axial magnetic field is applied outside the diamond sample to determine the two characteristic states of the NV color center and the target spin in the diamond sample. The energy level difference between the two characteristic states and the target spin are compared, and the energy level anti-crossing is determined based on the comparison results.

[0007] If there is energy level anti-crossing, the fluorescence intensity is determined based on the energy level anti-crossing, the NV color center is polarized by laser, and the initial fluorescence signal at the start of the pulse and the target fluorescence signal at the end of the pulse are determined. The normalized fluorescence signal is determined based on the initial fluorescence signal and the target fluorescence signal.

[0008] The layout probability of the composite quantum state is determined in the axial magnetic field. The coupling relationship between the fluorescence intensity and the fluorescence intensity of the magnetic field is determined based on the fluorescence intensity, the normalized fluorescence signal and the layout probability. The microwave frequency and the open-loop transfer function are determined. A bias magnetic field opposite to the axial magnetic field is applied based on the open-loop transfer function and the microwave frequency. The signal-to-noise ratio is adjusted based on the linear relationship between the laser relative intensity noise and the laser intensity.

[0009] A sine wave is used to modulate the measurement microwave frequency to determine the fluorescence signal function. The fluorescence signal function is then demodulated to determine the Fourier coefficients. Based on the Fourier coefficients, the adjusted signal-to-noise ratio, and the bias magnetic field, the NV color center current is measured.

[0010] Furthermore, when comparing the energy level difference between the two characteristic states with the target spin, and determining whether there is an energy level anti-crossover based on the comparison result, the process includes:

[0011] Determine the energy level difference between the characteristic states |0> and |−1> of the NV color center, and compare the energy level difference with the target spin;

[0012] If the energy level difference is not equal to the target spin, then it is determined that there is no energy level anti-crossing;

[0013] If the energy level difference is equal to the target spin, then an energy level anti-crossover is determined to exist.

[0014] Furthermore, if energy level anti-crossing exists, the fluorescence intensity is determined based on the energy level anti-crossing, including:

[0015] The fluorescence intensity at the anti-crossing of the energy level is determined based on the spin Hamiltonian, and the magnetic field component of the axial magnetic field in the z-axis direction is parallel to the NV axis.

[0016] Furthermore, when polarizing the NV color center using a laser and determining the initial fluorescence signal at the start of the pulse and the target fluorescence signal at the end of the pulse, and determining the normalized fluorescence signal based on the initial fluorescence signal and the target fluorescence signal, the process includes:

[0017] The initial fluorescence signal at the start of the pulse is denoted as Is, and the target fluorescence signal at the end of the pulse is denoted as Ir. The normalized fluorescence signal is determined according to the following formula:

[0018] ;

[0019] ;

[0020] in, This represents the normalized fluorescence signal, where a and b are constants. This represents the number of the current spin state in the characteristic state |0>, and |ψ(t)> represents the current spin state.

[0021] Furthermore, when determining the layout probability of the recombination quantum state in the axial magnetic field, and determining the coupling relationship between the fluorescence intensity and the fluorescence intensity of the magnetic field based on the fluorescence intensity, the normalized fluorescence signal, and the layout probability, the process includes:

[0022] The layout probability is determined by the following formula:

[0023] ;

[0024] in, This represents the number of layouts of the current spin state in the characteristic states |0, +1>. Indicates the electron spin-magnetic ratio. This represents the component of the axial magnetic field. δ represents the precession time, Bz represents the detuning relative to the resonance condition, and Bz represents the magnetic field component of the axial magnetic field in the z-axis direction.

[0025] The coupling relationship of the fluorescence intensity described by the magnetic field is determined according to the following formula:

[0026] ;

[0027] Where P(B, θ) represents the normalized fluorescence response function of the NV color center under the amplitude and direction angle of the axial magnetic field, and R represents the laser pump power. This indicates the pump saturation power.

[0028] Furthermore, when determining the microwave frequency and open-loop transfer function, and applying a bias magnetic field opposite to the axial magnetic field based on the open-loop transfer function and microwave frequency, the process includes:

[0029] The modulation parameters are set, and the modulated microwave frequency is determined according to the following formula:

[0030] ;

[0031] in, Let ω(t) represent the modulated microwave frequency, and A represent the modulation amplitude. φ represents the modulation frequency deviation, v represents the modulation frequency, φ represents the modulation phase, and t represents the modulation time.

[0032] The open-loop transfer function is determined by the following formula:

[0033] ;

[0034] ;

[0035] ;

[0036] Where G(s) represents the open-loop transfer function, and C represents the ODMR spectral contrast. This represents the average fluorescence intensity. Let H(s) represent the full width at half maximum (FWHM) of the ODMR spectrum, H(s) be the transfer function of the first-order demodulation low-pass filter, α represent the normalization coefficients of the first-order demodulation low-pass filter, and s represent the complex frequency variables in the Laplace domain. This indicates the cutoff frequency of the low-pass filter. This indicates the sampling frequency of the low-pass filter;

[0037] A bias magnetic field opposite to the axial magnetic field is applied based on the open-loop transfer function and the modulated microwave frequency.

[0038] Furthermore, when adjusting the signal-to-noise ratio based on the linear relationship between laser relative intensity noise and laser intensity, the following steps are included:

[0039] The laser is split into two beams using a beam splitter. One beam is used to excite the NV color center, while the other beam is used to collect time-domain variations. A multiplier is used to integrate the power of the two separated laser beams into one order of magnitude. A subtractor is used to determine the differential signal, and the differential signal is demodulated.

[0040] Furthermore, when using a sine wave to modulate the measurement microwave frequency to determine the fluorescence signal function, the following steps are included:

[0041] The fluorescence signal function is determined according to the following formula:

[0042] ;

[0043] ;

[0044] ;

[0045] Where v(t) represents the modulated measurement microwave frequency, v start The starting frequency is given by k, the microwave frequency step is given by t, the modulation time is given by Dev, and the modulation depth is given by w. m The frequency is the sinusoidal modulation frequency, and v0 represents the resonant center frequency of the NV color center. Indicates the detuning frequency. S(∞) represents the fluorescence signal function, S(∞) represents the fluorescence signal reference value far from the NV color center resonance condition, and C represents the ODMR spectral contrast. This indicates the full width at half maximum (FWHM) of the ODMR spectrum.

[0046] Furthermore, when demodulating the fluorescence signal function and determining the Fourier coefficients, the process includes:

[0047] The fluorescence signal function is subjected to Fourier expansion to determine the first harmonic component after demodulation and filtering. Fourier coefficients are then determined based on the first harmonic component, and these coefficients are determined according to the following formula:

[0048] ;

[0049] ;

[0050] ;

[0051] Where S(v) represents the first harmonic component, S(∞) represents the fluorescence signal reference value far from the NV color center resonance condition, and C represents the ODMR spectral contrast. Indicates the full width at half maximum (FWHM) of the ODMR spectrum. γ represents the detuning frequency, Dev represents the modulation depth, a0 represents the zeroth harmonic coefficient in the Fourier expansion, a1 represents the first harmonic coefficient in the Fourier expansion, and γ represents the composite parameter. u represents an auxiliary parameter. η represents the normalized detuning parameter. β represents the normalized linewidth parameter. .

[0052] Compared with existing technologies, the beneficial effects of this invention are as follows: By applying an axial magnetic field to the outside of the diamond sample, the energy level difference between the two characteristic states of the NV color center is compared with the target spin in the diamond sample, causing the NV color center to operate in the anti-crossover region of energy levels that is sensitive to changes in the magnetic field. This improves the sensitivity of current measurement to changes in weak magnetic fields. Under the condition of energy level anti-crossover, the change in fluorescence intensity is determined based on the energy level anti-crossover. A normalized fluorescence signal is constructed by acquiring the initial fluorescence signal at the start of the pulse and the target fluorescence signal after the end of the pulse. This eliminates the influence of non-target factors such as laser power fluctuations and changes in detection efficiency on the measurement results, improves the stability of the fluorescence signal, and further enhances the stability of the fluorescence signal. By determining the layout probability of the composite quantum state in the magnetic field and establishing the coupling relationship between the magnetic field and fluorescence intensity, changes in the magnetic field can be mapped to changes in the fluorescence signal, thereby enhancing the resolution of current information in the optical signal. At the same time, by determining the microwave frequency and open-loop transfer function to apply a bias magnetic field opposite to the axial magnetic field, the NV color center is kept in the linear region of the fluorescence response, avoiding the risk of fluorescence saturation or sensitivity reduction due to strong magnetic fields. Sinusoidal modulation is applied to the measurement microwave frequency to transfer the current signal in the low-frequency noise environment to the vicinity of the modulation frequency. Combined with demodulation and Fourier coefficient extraction, the influence of low-frequency noise and drift on the measurement results is suppressed, further improving the signal-to-noise ratio and accuracy of current measurement.

[0053] On the other hand, this application also provides a system for improving the accuracy of diamond NV center current measurement, for applying the above-mentioned method for improving the accuracy of diamond NV center current measurement, including:

[0054] The energy level determination unit is configured to apply an axial magnetic field outside the diamond sample, determine the two characteristic states of the NV color center and the target spin in the diamond sample, compare the energy level difference between the two characteristic states and the target spin, and determine whether there is an energy level anti-crossing based on the comparison result.

[0055] The fluorescence processing unit is configured to determine the fluorescence intensity based on the energy level anti-crossing if energy level anti-crossing exists, polarize the NV color center with a laser, determine the initial fluorescence signal at the start of the pulse and the target fluorescence signal after the end of the pulse, and determine the normalized fluorescence signal based on the initial fluorescence signal and the target fluorescence signal.

[0056] A high-precision magnetic field decoupling unit is configured to determine the layout probability of the composite quantum state in the axial magnetic field, determine the coupling relationship of the fluorescence intensity of the magnetic field based on the fluorescence intensity, the normalized fluorescence signal and the layout probability, determine the microwave frequency and the open-loop transfer function, apply a bias magnetic field opposite to the axial magnetic field based on the open-loop transfer function and the microwave frequency, and adjust the signal-to-noise ratio based on the linear relationship between the laser relative intensity noise and the laser intensity.

[0057] The current measurement unit is configured to modulate the measurement microwave frequency with a sine wave to determine the fluorescence signal function, demodulate the fluorescence signal function to determine the Fourier coefficients, and measure the NV color center current based on the Fourier coefficients, the adjusted signal-to-noise ratio, and the bias magnetic field.

[0058] It is understandable that the above-mentioned method and system for improving the accuracy of diamond NV color center current measurement have the same beneficial effects, and will not be elaborated further here. Attached Figure Description

[0059] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0060] Figure 1 A flowchart of a method for improving the accuracy of diamond NV color center current measurement provided in an embodiment of the present invention;

[0061] Figure 2 A schematic diagram of the NV color center ground state energy level provided in an embodiment of the present invention;

[0062] Figure 3 This is a schematic diagram of the ODMR spectrum provided in an embodiment of the present invention;

[0063] Figure 4 This is a schematic diagram illustrating the evolution of frequency with magnetic field, provided in an embodiment of the present invention.

[0064] Figure 5 This is a schematic diagram of dual-path negative feedback provided in an embodiment of the present invention;

[0065] Figure 6 This is a schematic diagram of the PID output when a weak magnetic field acts on an NV color center, as provided in an embodiment of the present invention.

[0066] Figure 7 This is a schematic diagram illustrating the relationship between the magnetic field and the feedback voltage when a weak magnetic field acts on an NV color center, as provided in an embodiment of the present invention.

[0067] Figure 8 A schematic diagram of the laser and fluorescence phase extinction path is provided for embodiments of the present invention;

[0068] Figure 9 This is a functional block diagram of a system for improving the accuracy of diamond NV color center current measurement, provided as an embodiment of the present invention.

[0069] The components include: 1. Laser; 2. Beam splitter; 3. Diamond; 4. Filter; 5. Photodetector. Detailed Implementation

[0070] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0071] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0072] See Figure 1 As shown in some embodiments of this application, a method for improving the accuracy of diamond NV color center current measurement includes:

[0073] S100: Apply an axial magnetic field to the outside of the diamond sample to determine the two characteristic states of the NV color center and the target spin in the diamond sample. Compare the energy level difference between the two characteristic states with the target spin, and determine whether there is an energy level anti-crossing based on the comparison result.

[0074] S200: If there is energy level anti-crossing, determine the fluorescence intensity based on the energy level anti-crossing, use laser to polarize the NV color center, and determine the initial fluorescence signal at the beginning of the pulse and the target fluorescence signal after the end of the pulse. Determine the normalized fluorescence signal based on the initial fluorescence signal and the target fluorescence signal.

[0075] S300: Determine the layout probability of the composite quantum state in the axial magnetic field, determine the coupling relationship between the magnetic field and fluorescence intensity based on fluorescence intensity, normalized fluorescence signal and layout probability, determine the microwave frequency and open-loop transfer function, apply a bias magnetic field opposite to the axial magnetic field based on the open-loop transfer function and microwave frequency, and adjust the signal-to-noise ratio based on the linear relationship between laser relative intensity noise and laser intensity.

[0076] S400: The measurement microwave frequency is modulated using a sine wave to determine the fluorescence signal function, the fluorescence signal function is demodulated to determine the Fourier coefficients, and the NV color center current is measured based on the Fourier coefficients, the adjusted signal-to-noise ratio, and the bias magnetic field.

[0077] Specifically, based on the spin level structure and photoinduced spin of diamond NV centers, and by modeling the fluorescence response characteristics under anti-crossing conditions, combined with microwave modulation and demodulation, the high-precision measurement of NV center currents in complex magnetic field environments was achieved. An axial magnetic field was applied outside the diamond sample, causing Zeeman splitting of the NV center electron spin levels. The two characteristic states of the NV center were compared with the target spin in the diamond sample. When the axial magnetic field satisfied the matching relationship between zero-field splitting, Zeeman splitting, and hyperfine interaction, the two characteristic states of the NV center underwent anti-crossing. The appearance of anti-crossing signifies that the NV center system has entered a strong spin mixing region. In this region, the axial magnetic field or environmental perturbations affect the spin state distribution and fluorescence behavior. After confirming the existence of energy level anti-crossing, the fluorescence decay mechanism of the NV center under the action of a large magnetic field was analyzed based on the energy level anti-crossing. The NV center was polarized by laser, and the initial fluorescence signal was acquired at the beginning of the pulse and the target fluorescence signal was acquired at the end of the pulse. The normalized fluorescence signal was obtained by normalizing the two signals to eliminate the influence of optical system gain fluctuations and detection efficiency changes on the measurement results, so that the fluorescence change is only related to the spin state evolution. Furthermore, the layout probability of the composite quantum state is determined under axial magnetic field conditions, and the layout probability is combined with fluorescence intensity and normalized fluorescence signal to construct a coupling relationship between magnetic field and fluorescence intensity. This coupling relationship maps changes in the external magnetic field to changes in fluorescence response, thereby establishing a quantitative correlation between current, magnetic field, and fluorescence. Simultaneously, the microwave frequency and open-loop transfer function are determined based on the coupling relationship. The frequency response is characterized by the open-loop transfer function, and a bias magnetic field opposite to the axial magnetic field is applied. This bias magnetic field is used to cancel the background magnetic field generated by the strong current, avoiding fluorescence signal attenuation and signal-to-noise ratio reduction due to excessive magnetic field strength. Utilizing the linear relationship between laser relative intensity noise and laser intensity, the matching relationship between the laser signal and fluorescence signal is adjusted to achieve cancellation of laser intensity fluctuation noise, thereby improving the signal-to-noise ratio at the optical level. Subsequently, a sine wave is used to modulate the measurement microwave frequency, shifting the current magnetic field information originally in the low-frequency region to near the modulation frequency. By demodulating the fluorescence signal function, the response characteristics of the modulation signal in the frequency domain are extracted, and the Fourier coefficients are obtained by performing Fourier expansion on the demodulated signal. Fourier coefficients reflect the degree of response of fluorescence signals to microwave frequency detuning. Among them, the first harmonic component is most sensitive to detuning changes. Based on the Fourier coefficients, the adjusted signal-to-noise ratio, and the bias magnetic field, the NV color center current is measured to achieve high-precision current detection.

[0078] Understandably, by introducing a bias magnetic field opposite to the axial magnetic field under anti-crossing conditions, the NV color center always operates in a highly sensitive region, reducing the non-target modulation influence of the background magnetic field and strong current magnetic field on the fluorescence signal. Furthermore, by normalizing the initial fluorescence signal and the target fluorescence signal, the influence of optical system fluctuations and changes in detection efficiency on the measurement results is weakened, further improving the stability of current measurement. By utilizing microwave frequency modulation and Fourier coefficient demodulation, the small magnetic field changes caused by the current are transformed into changes in the first harmonic component, improving the detection sensitivity to weak current changes. Moreover, by combining the cancellation of laser relative intensity noise and frequency domain demodulation, noise is suppressed at both the optical and signal processing levels, improving the signal-to-noise ratio of NV color center current measurement. This enables stable current measurement even in strong magnetic field and complex noise environments, meeting the requirements for high-precision current measurement.

[0079] See Figure 2 As shown, in some embodiments of this application, when comparing the energy level difference between two characteristic states with the target spin and determining whether there is an energy level anti-crossing based on the comparison result, the process includes: determining the energy level difference between the characteristic states |0> and |−1> of the NV color center, and comparing the energy level difference with the target spin. If the energy level difference is not equal to the target spin, it is determined that there is no energy level anti-crossing; if the energy level difference is equal to the target spin, it is determined that there is an energy level anti-crossing.

[0080] Specifically, an axial magnetic field is applied outside the diamond sample, and the spin time of the NV axis is monitored. |0> and |−1> are two spin-projected quantum states of the spin triplet state of the NV color center, corresponding to the spin angular momentum projection value m along the NV axis. s =0 and m s =−1. When the two characteristic states |0> and |−1> of the NV center are equal to the target spin, cross-relaxation will occur, which will lead to an increase in the relaxation rate of the NV center. That is, when the magnetic field strength exceeds 460 Gs, which corresponds to the resonance spectrum of the spin with a transition frequency exceeding 1300 MHz, in order to detect NMR, the NV spin transition frequency must match the Lamour precession frequency of the target spin, and the magnetic field component in the z-axis direction of the axial magnetic field must be about 1024 Gs. Then the two characteristic states |0> and |−1> will become degenerate, that is, anti-crossing (ground-state level anticrossing, GSLAC) relaxation phenomenon will occur, which is energy level anti-crossing. Otherwise, under the action of the current axial magnetic field, the two characteristic states have not reached a degenerate or quasi-degenerate state, and the system is still in the normal energy level splitting range. At this time, the axial magnetic field or hyperfine interaction only produces a small perturbation to the energy level, which is difficult to cause spin state mixing. Therefore, the conditions for energy level anti-crossing are not met, and energy level anti-crossing does not exist.

[0081] In some embodiments of this application, if there is an energy level anti-crossing, the fluorescence intensity is determined based on the energy level anti-crossing, including: determining the fluorescence intensity at the energy level anti-crossing based on the spin Hamiltonian, and the magnetic field component of the axial magnetic field in the z-axis direction is parallel to the NV axis.

[0082] Specifically, the fluorescence intensity distribution of the NV color center under the influence of a large magnetic field can be estimated at GSLAC, thus providing a data basis for measuring large currents. By solving the eigenvalues ​​of the spin Hamiltonian, the energy spectrum of the NV electron spin ground state near GSLAC can be obtained.

[0083] In some embodiments of this application, when polarizing the NV color center using a laser and determining the initial fluorescence signal at the start of the pulse and the target fluorescence signal at the end of the pulse, and determining the normalized fluorescence signal based on the initial fluorescence signal and the target fluorescence signal, the method includes: denoting the initial fluorescence signal at the start of the pulse as Is, and the target fluorescence signal at the end of the pulse as Ir, and determining the normalized fluorescence signal according to the following formula:

[0084] ;

[0085] ;

[0086] in, This represents the normalized fluorescence signal, where a and b are constants. This represents the number of the current spin state in the characteristic state |0>, and |ψ(t)> represents the current spin state.

[0087] Specifically, the laser polarizes the NV color center to the |0> state. After a laser duration of t, the remaining number of layouts in the |0> state is determined. It's important to note that the laser duration t here is not the modulation time t; it simply indicates that both are functions of time. The fluorescence signal at the start of the pulse is denoted as Is, and the fluorescence signal at the end of the pulse is denoted as Ir. It is the number of the current spin state |ψ(t)> in the |0> state, and a is approximately equal to 1 and b is approximately equal to 0.3. a and b are both constants. The initial number of the spin state P0(0) is estimated by the time trajectory, which is the normalized fluorescence signal.

[0088] See Figure 3-4 As shown, in some embodiments of this application, determining the layout probability of the recombination quantum state in an axial magnetic field, and determining the coupling relationship between the magnetic field and fluorescence intensity based on fluorescence intensity, normalized fluorescence signal, and layout probability, includes:

[0089] The layout probability is determined by the following formula:

[0090] ;

[0091] in, This represents the number of layouts of the current spin state in the characteristic states |0, +1>. Indicates the electron spin-magnetic ratio. This represents the component of the axial magnetic field. δ represents the precession time, Bz represents the detuning relative to the resonance condition, and Bz represents the magnetic field component of the axial magnetic field in the z-axis direction.

[0092] The coupling relationship of the fluorescence intensity described by the magnetic field is determined according to the following formula:

[0093] ;

[0094] Where P(B, θ) represents the normalized fluorescence response function of the NV color center under the amplitude and direction angle of the axial magnetic field, and R represents the laser pump power. This indicates the pump saturation power.

[0095] Specifically, under normal circumstances, spin configurations exhibit an exponential decay and tend towards thermal equilibrium, while in a magnetic field, for 14 The calculation of the Hamiltonian of the spin of the NV color center can be simplified to:

[0096] ;

[0097] ;

[0098] ;

[0099] Here, HR represents the effective Hamiltonian of the NV color center spin at the anti-crossing energy level. Indicates the electron spin-magnetic ratio. The components of the axial magnetic field are represented by: i (imaginary unit), e (natural constant), θ (direction angle of the axial magnetic field), δ (detuning relative to the resonance condition), Bx (magnetic field component in the x-axis direction), By (magnetic field component in the y-axis direction), and Bz (magnetic field component in the z-axis direction).

[0100] Understandably, the axial magnetic field leads to the mixing of the |0,+1> state and the |-1,+1> state. Assuming that the pump light always initializes the NV spin of the |0,+1> state and determines the color center layout in the same energy level state, the number of the current spin state in the characteristic state |0,+1> can be obtained immediately after initialization and precession time. This determines the coupling relationship between the magnetic field and fluorescence intensity, which is the normalized fluorescence response function of the NV color center under the amplitude and direction angle of the axial magnetic field. As the axial magnetic field increases, the fluorescence intensity decreases accordingly. Therefore, in order to avoid the fluorescence intensity being too weak and causing a decrease in the signal-to-noise ratio when measuring currents exceeding 1200A, a bias magnetic field opposite to the axial magnetic field needs to be applied to increase the fluorescence intensity and thus improve the accuracy of current measurement.

[0101] See Figure 5-7 As shown, in some embodiments of this application, when determining the microwave frequency and open-loop transfer function, and applying a bias magnetic field opposite to the axial magnetic field based on the open-loop transfer function and microwave frequency, the process includes: setting modulation parameters, wherein the modulated microwave frequency is determined according to the following formula:

[0102] ;

[0103] in, Let ω(t) represent the modulated microwave frequency, and A represent the modulation amplitude. φ represents the modulation frequency deviation, v represents the modulation frequency, φ represents the modulation phase, and t represents the modulation time.

[0104] The open-loop transfer function is determined by the following formula:

[0105] ;

[0106] ;

[0107] ;

[0108] Where G(s) represents the open-loop transfer function, and C represents the ODMR spectral contrast. This represents the average fluorescence intensity. Let H(s) represent the full width at half maximum (FWHM) of the ODMR spectrum, H(s) be the transfer function of the first-order demodulation low-pass filter, α represent the normalization coefficients of the first-order demodulation low-pass filter, and s represent the complex frequency variables in the Laplace domain. This indicates the cutoff frequency of the low-pass filter. The sampling frequency of the low-pass filter is represented by a bias magnetic field applied based on the open-loop transfer function and the modulated microwave frequency, which is opposite to the axial magnetic field.

[0109] Specifically, by adjusting the microwave frequency PID with negative feedback, the resonant frequency of the ODMR spectrum can be tracked in real time without being affected by the linear range of the demodulated signal. Thus, the offset of the resonant frequency can be directly located to achieve current measurement in ultra-large magnetic fields. However, in the construction of the overall current measurement system, there are still a number of noises that need to be suppressed, such as: light source fluctuation noise caused by high-power lasers, photon shot noise caused by weak fluorescence collection efficiency, and noise caused by detectors.

[0110] See Figure 8 As shown, in some embodiments of this application, when adjusting the signal-to-noise ratio based on the linear relationship between the relative intensity noise and the laser intensity, the method includes: using a beam splitter to split the laser into two beams, one beam being used to excite the NV color center and the other beam being used to collect time-domain variations; using a multiplier to integrate the power of the two separated laser beams into one order of magnitude; determining the differential signal based on a subtractor; and demodulating the differential signal.

[0111] Specifically, in current measurement of ultra-large magnetic fields, factors such as source fluctuation noise from high-power lasers, photon shot noise from weak fluorescence collection efficiency, and detector noise can affect the accuracy of current measurement. When the laser intensity is higher than the fluorescence signal intensity, based on the linear relationship between laser relative intensity noise and laser intensity, and the 1 / 2 power correlation between shot noise and intensity, the overall signal-to-noise ratio is improved by increasing the laser intensity. The laser serves as the pump source, and after polarization adjustment by a half-wave plate, it enters a beam splitter. After beam splitting, one path is used to directly excite the fluorescence generated by the NV color centers in diamond, while the other path serves as a laser reference path. The time-domain variation of laser power is recorded. After the laser irradiates the diamond, the fluorescence generated by the NV color center is converged by the structure and filtered to remove residual laser light before being detected by a photodetector. Since the fluorescence power and the laser power differ by several orders of magnitude, the two photoelectric signals are amplitude matched and normalized to bring them within the same order of magnitude. Then, the fluorescence signal and the laser signal are differentially divided by a subtractor to eliminate the influence of laser power fluctuations on the measurement results, thus obtaining a differential signal. The differential signal is then input to a lock-in amplifier for demodulation, thereby extracting the corresponding time-domain and frequency-domain magnetic field signals, which improves the accuracy of the diamond NV color center current measurement. In high-current electromagnetic field environments, the noise energy in the mid-frequency band accounts for a relatively high proportion. The low-frequency magnetic field signal is shifted to the high-frequency band by carrier modulation to avoid the noise-dominated frequency domain. Then, the signal is restored to the baseband frequency through synchronous demodulation. During this process, the low-frequency noise is modulated by the high-frequency carrier, resulting in spectral shift and decoupling from the signal. While suppressing the low-frequency noise, lock-in amplification is used to filter out high-order harmonics. Ultimately, the mid- and low-frequency noise of NV magnetic intensity under dynamic magnetic field environment is suppressed, thereby improving the accuracy of NV color center current measurement.

[0112] In some embodiments of this application, when using a sine wave to modulate the measurement microwave frequency to determine the fluorescence signal function, the fluorescence signal function is determined according to the following formula:

[0113] ;

[0114] ;

[0115] ;

[0116] Where v(t) represents the modulated measurement microwave frequency, v start The starting frequency is given by k, the microwave frequency step is given by t, the modulation time is given by Dev, and the modulation depth is given by w. m The frequency is the sinusoidal modulation frequency, and v0 represents the resonant center frequency of the NV color center. Indicates the detuning frequency. S(∞) represents the fluorescence signal function, S(∞) represents the fluorescence signal reference value far from the NV color center resonance condition, and C represents the ODMR spectral contrast. This indicates the full width at half maximum (FWHM) of the ODMR spectrum.

[0117] In some embodiments of this application, when demodulating the fluorescence signal function and determining the Fourier coefficients, the process includes: performing a Fourier expansion on the fluorescence signal function to determine the first harmonic component after demodulation and filtering, and determining the Fourier coefficients based on the first harmonic component. The Fourier coefficients are determined according to the following formula:

[0118] ;

[0119] ;

[0120] ;

[0121] Where S(v) represents the first harmonic component, S(∞) represents the fluorescence signal reference value far from the NV color center resonance condition, and C represents the ODMR spectral contrast. Indicates the full width at half maximum (FWHM) of the ODMR spectrum. γ represents the detuning frequency, Dev represents the modulation depth, a0 represents the zeroth harmonic coefficient in the Fourier expansion, a1 represents the first harmonic coefficient in the Fourier expansion, and γ represents the composite parameter. u represents an auxiliary parameter. η represents the normalized detuning parameter. β represents the normalized linewidth parameter. .

[0122] Specifically, under frequency sweep conditions, a sine wave is used to modulate the measurement microwave frequency. The starting frequency is the reference value of the microwave source, and the modulated microwave frequency is the instantaneous frequency actually applied to the NV color center. The modulated measurement microwave frequency is the segment of the modulated microwave frequency used for measurement. After determining the ODMR spectral contrast and the full width at half maximum (FWHM) of the ODMR spectrum, the zeroth and first harmonic coefficients in the Fourier expansion are given by the modulation depth (Dev) and the detuning frequency. The function obtains the modulation parameters under high current electric field conditions through the zero-order harmonic coefficient and the first-order harmonic coefficient, which improves the stability and reliability of the current sensor. At the same time, based on the real-time tracking of the dual-channel resonant frequency, the PID control combined with digital signals feeds the two resonant frequency offsets of the ODMR spectrum back to the microwave, and then compensates for them by applying NV spin. This achieves real-time tracking of the resonant frequency, eliminates the influence of factors such as temperature on the accuracy of current measurement, and thus improves the accuracy of current measurement.

[0123] In summary, the beneficial effects of this invention are as follows: By applying an axial magnetic field outside the diamond sample, the energy level difference between the two characteristic states of the NV color center is compared with the target spin in the diamond sample, causing the NV color center to operate in the anti-crossover region of the energy levels, which is sensitive to changes in the magnetic field. This improves the sensitivity of current measurement to changes in weak magnetic fields. Under the condition of energy level anti-crossover, the change in fluorescence intensity is determined based on the energy level anti-crossover. A normalized fluorescence signal is constructed by acquiring the initial fluorescence signal at the start of the pulse and the target fluorescence signal after the end of the pulse. This eliminates the influence of non-target factors such as laser power fluctuations and changes in detection efficiency on the measurement results, improves the stability of the fluorescence signal, and further enhances the effectiveness of the invention. The layout probability of the composite quantum state is determined in the field, and the coupling relationship between the magnetic field and fluorescence intensity is established, so that changes in the magnetic field can be mapped to changes in the fluorescence signal, thereby enhancing the resolution of current information in the optical signal. At the same time, by determining the microwave frequency and open-loop transfer function, a bias magnetic field opposite to the axial magnetic field is applied, so that the NV color center is kept in the linear region of the fluorescence response, avoiding the risk of fluorescence saturation or sensitivity reduction due to strong magnetic fields. Sinusoidal modulation is applied to the measurement microwave frequency to transfer the current signal in the low-frequency noise environment to the vicinity of the modulation frequency. Combined with demodulation and Fourier coefficient extraction, the influence of low-frequency noise and drift on the measurement results is suppressed, further improving the signal-to-noise ratio and accuracy of current measurement.

[0124] In another preferred embodiment based on the above embodiments, see [reference] Figure 9 As shown, this embodiment provides a system for improving the measurement accuracy of diamond NV center current, used in applying the above-described method for improving the measurement accuracy of diamond NV center current, including:

[0125] The energy level determination unit is configured to apply an axial magnetic field outside the diamond sample, determine the two characteristic states of the NV color center and the target spin in the diamond sample, compare the energy level difference between the two characteristic states with the target spin, and determine whether there is an energy level anti-crossing based on the comparison result.

[0126] The fluorescence processing unit is configured to determine the fluorescence intensity based on the energy level anti-crossing if energy level anti-crossing exists, polarize the NV color center with a laser, determine the initial fluorescence signal at the start of the pulse and the target fluorescence signal at the end of the pulse, and determine the normalized fluorescence signal based on the initial fluorescence signal and the target fluorescence signal.

[0127] The high-precision magnetic field decoupling unit is configured to determine the layout probability of the composite quantum state in the axial magnetic field, determine the coupling relationship between the magnetic field and fluorescence intensity based on the fluorescence intensity, normalized fluorescence signal and layout probability, determine the microwave frequency and open-loop transfer function, apply a bias magnetic field opposite to the axial magnetic field based on the open-loop transfer function and microwave frequency, and adjust the signal-to-noise ratio based on the linear relationship between the laser relative intensity noise and the laser intensity.

[0128] The current measurement unit is configured to modulate the measurement microwave frequency with a sine wave to determine the fluorescence signal function, demodulate the fluorescence signal function to determine the Fourier coefficients, and measure the NV color center current based on the Fourier coefficients, the adjusted signal-to-noise ratio, and the bias magnetic field.

[0129] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program goods according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0130] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for improving the accuracy of diamond NV color center current measurement, characterized in that, include: An axial magnetic field is applied outside the diamond sample to determine the two characteristic states of the NV color center and the target spin in the diamond sample. The energy level difference between the two characteristic states and the target spin are compared, and the energy level anti-crossing is determined based on the comparison results. If there is energy level anti-crossing, the fluorescence intensity is determined based on the energy level anti-crossing, the NV color center is polarized by laser, and the initial fluorescence signal at the start of the pulse and the target fluorescence signal at the end of the pulse are determined. The normalized fluorescence signal is determined based on the initial fluorescence signal and the target fluorescence signal. The layout probability of the composite quantum state is determined in the axial magnetic field. The coupling relationship between the fluorescence intensity and the fluorescence intensity of the magnetic field is determined based on the fluorescence intensity, the normalized fluorescence signal and the layout probability. The microwave frequency and the open-loop transfer function are determined. A bias magnetic field opposite to the axial magnetic field is applied based on the open-loop transfer function and the microwave frequency. The signal-to-noise ratio is adjusted based on the linear relationship between the laser relative intensity noise and the laser intensity. A sine wave is used to modulate the measurement microwave frequency to determine the fluorescence signal function. The fluorescence signal function is then demodulated to determine the Fourier coefficients. Based on the Fourier coefficients, the adjusted signal-to-noise ratio, and the bias magnetic field, the NV color center current is measured. When determining the microwave frequency and open-loop transfer function, and applying a bias magnetic field opposite to the axial magnetic field based on the open-loop transfer function and microwave frequency, the process includes: The modulation parameters are set, and the modulated microwave frequency is determined according to the following formula: ； in, Let ω(t) represent the modulated microwave frequency, and A represent the modulation amplitude. φ represents the modulation frequency deviation, v represents the modulation frequency, φ represents the modulation phase, and t represents the modulation time. The open-loop transfer function is determined by the following formula: ； ； ； Where G(s) represents the open-loop transfer function, and C represents the ODMR spectral contrast. This represents the average fluorescence intensity. Let H(s) represent the full width at half maximum (FWHM) of the ODMR spectrum, H(s) be the transfer function of the first-order demodulation low-pass filter, α represent the normalization coefficients of the first-order demodulation low-pass filter, and s represent the complex frequency variables in the Laplace domain. This indicates the cutoff frequency of the low-pass filter. This indicates the sampling frequency of the low-pass filter; A bias magnetic field opposite to the axial magnetic field is applied based on the open-loop transfer function and the modulated microwave frequency.

2. The method for improving the accuracy of diamond NV color center current measurement according to claim 1, characterized in that, When comparing the energy level difference between the two characteristic states with the target spin, and determining whether there is an energy level anti-crossover based on the comparison result, the process includes: Determine the energy level difference between the characteristic states |0> and |−1> of the NV color center, and compare the energy level difference with the target spin; If the energy level difference is not equal to the target spin, then it is determined that there is no energy level anti-crossing; If the energy level difference is equal to the target spin, then an energy level anti-crossover is determined to exist.

3. The method for improving the accuracy of diamond NV color center current measurement according to claim 2, characterized in that, If anti-crossing of energy levels exists, the fluorescence intensity is determined based on the anti-crossing of energy levels, including: The fluorescence intensity at the anti-crossing of the energy level is determined based on the spin Hamiltonian, and the magnetic field component of the axial magnetic field in the z-axis direction is parallel to the NV axis.

4. The method for improving the accuracy of diamond NV color center current measurement according to claim 3, characterized in that, When polarizing the NV color center using a laser, and determining the initial fluorescence signal at the start of the pulse and the target fluorescence signal at the end of the pulse, and determining the normalized fluorescence signal based on the initial fluorescence signal and the target fluorescence signal, the process includes: The initial fluorescence signal at the start of the pulse is denoted as Is, and the target fluorescence signal at the end of the pulse is denoted as Ir. The normalized fluorescence signal is determined according to the following formula: ； ； in, This represents the normalized fluorescence signal, where a and b are constants. This represents the number of the current spin state |ψ(t)> in the |0> state, where |ψ(t)> represents the current spin state.

5. The method for improving the accuracy of diamond NV color center current measurement according to claim 4, characterized in that, Determining the layout probability of the recombination quantum state in the axial magnetic field, and determining the coupling relationship between the fluorescence intensity, the normalized fluorescence signal, and the layout probability of the magnetic field, includes: The layout probability is determined by the following formula: ； in, This represents the number of the current spin state's layout in the composite eigenstates of |0> and |+1>. Indicates the electron spin-magnetic ratio. This represents the component of the axial magnetic field. δ represents the precession time, Bz represents the detuning relative to the resonance condition, and Bz represents the magnetic field component of the axial magnetic field in the z-axis direction. The coupling relationship of the fluorescence intensity described by the magnetic field is determined according to the following formula: ； Where P(B, θ) represents the normalized fluorescence response function of the NV color center under the amplitude and direction angle of the axial magnetic field, and R represents the laser pump power. This indicates the pump saturation power.

6. The method for improving the accuracy of diamond NV color center current measurement according to claim 5, characterized in that, When adjusting the signal-to-noise ratio based on the linear relationship between laser relative intensity noise and laser intensity, the following are included: The laser is split into two beams using a beam splitter. One beam is used to excite the NV color center, while the other beam is used to collect time-domain variations. A multiplier is used to integrate the power of the two separated laser beams into one order of magnitude. A subtractor is used to determine the differential signal, and the differential signal is demodulated.

7. The method for improving the accuracy of diamond NV color center current measurement according to claim 6, characterized in that, When using a sine wave to modulate the measurement microwave frequency to determine the fluorescence signal function, the following steps are included: The fluorescence signal function is determined according to the following formula: ； ； ； Where v(t) represents the modulated measurement microwave frequency, v start The starting frequency is given by k, the microwave frequency step is given by t, the modulation time is given by Dev, and the modulation depth is given by w. m The frequency is the sinusoidal modulation frequency, and v0 represents the resonant center frequency of the NV color center. Indicates the detuning frequency. S(∞) represents the fluorescence signal function, S(∞) represents the fluorescence signal reference value far from the NV color center resonance condition, and C represents the ODMR spectral contrast. This indicates the full width at half maximum (FWHM) of the ODMR spectrum.

8. The method for improving the accuracy of diamond NV color center current measurement according to claim 7, characterized in that, Demodulating the fluorescence signal function and determining the Fourier coefficients includes: The fluorescence signal function is subjected to Fourier expansion to determine the first harmonic component after demodulation and filtering. Fourier coefficients are then determined based on the first harmonic component, and these coefficients are determined according to the following formula: ； ； ； Where S(v) represents the first harmonic component, S(∞) represents the fluorescence signal reference value far from the NV color center resonance condition, and C represents the ODMR spectral contrast. Indicates the full width at half maximum (FWHM) of the ODMR spectrum. γ represents the detuning frequency, Dev represents the modulation depth, a0 represents the zeroth harmonic coefficient in the Fourier expansion, a1 represents the first harmonic coefficient in the Fourier expansion, and γ represents the composite parameter. u represents an auxiliary parameter. η represents the normalized detuning parameter. β represents the normalized linewidth parameter. .

9. A system for improving the accuracy of diamond NV center current measurement, used in applying the method for improving the accuracy of diamond NV center current measurement as described in any one of claims 1-8, characterized in that, include: The energy level determination unit is configured to apply an axial magnetic field outside the diamond sample, determine the two characteristic states of the NV color center and the target spin in the diamond sample, compare the energy level difference between the two characteristic states and the target spin, and determine whether there is an energy level anti-crossing based on the comparison result. The fluorescence processing unit is configured to determine the fluorescence intensity based on the energy level anti-crossing if energy level anti-crossing exists, polarize the NV color center with a laser, determine the initial fluorescence signal at the start of the pulse and the target fluorescence signal after the end of the pulse, and determine the normalized fluorescence signal based on the initial fluorescence signal and the target fluorescence signal. A high-precision magnetic field decoupling unit is configured to determine the layout probability of the composite quantum state in the axial magnetic field, determine the coupling relationship of the fluorescence intensity of the magnetic field based on the fluorescence intensity, the normalized fluorescence signal and the layout probability, determine the microwave frequency and the open-loop transfer function, apply a bias magnetic field opposite to the axial magnetic field based on the open-loop transfer function and the microwave frequency, and adjust the signal-to-noise ratio based on the linear relationship between the laser relative intensity noise and the laser intensity. The current measurement unit is configured to modulate the measurement microwave frequency with a sine wave to determine the fluorescence signal function, demodulate the fluorescence signal function to determine the Fourier coefficients, and measure the NV color center current based on the Fourier coefficients, the adjusted signal-to-noise ratio, and the bias magnetic field.

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