Gyroscope based on NV center in diamond

Abstract

The invention provides a gyroscope based on an NV center in diamond, and relates to the field of instrument manufacturing, in particular to a quantum gyroscope based on a nitrogen-vacancy center in diamond, which comprises diamond, two light sources with the wavelength of 450-650nm and an optical system for guiding light of the light sources to the diamond. For two independent sets of NV centers illuminated by light, a sufficient optical radiation power density is provided to make the electron spin of the NV centers orthogonal to the NV center axis. The fluorescence of the NV center in the diamond is directed to a photodetector of a second optical system and the fluorescence intensity is recorded. The gyroscope includes at least one microwave radiation source, at least one high frequency radiation source, a constant magnetic field source, and a control circuit. The technical effect is to reduce rotation angular velocity measurement errors caused by magnetic field fluctuations in a diamond region.

Description

Technical Field

[0001] The present invention relates to the field of instrument manufacturing, in particular to a quantum gyroscope based on nitrogen-vacancy centers (NV centers) in diamond. Background Art

[0002] Patent RU2661442 (application number: 2016116860, application date: November 28, 2016, applicant: SensorSpin Technologies LLC) discloses a technical solution. The gyroscope includes a diamond plate, a green light source, an optical system for guiding the green light to the diamond plate, and a nitrogen-vacancy color center (NV center) in the diamond plate. Figure 1 ) fluorescence photodetector, an optical element for guiding fluorescence from the diamond plate to the photodetector, an ultra-high frequency radiation source, a high frequency radiation source, and a constant magnetic field source. The gyroscope uses the spin of the NV center in the diamond as a sensing element, and the energy-saving microwave antenna has a strong and uniform longitudinal field in the entire volume of the crystal and realizes frequency tuning, and the microwave field frequency is associated with the transition frequency of the NV center, which has the technical effect of reducing the volume of the sensor element and improving the spectral sensitivity. However, the disadvantage of this technical solution is that it is easily affected by external magnetic field fluctuations, resulting in the gyroscope being unable to achieve high spectral sensitivity when the external magnetic field is unstable. Summary of the invention

[0003] The present invention aims to solve the technical problem of measuring the rotational angular velocity of a gyroscope under arbitrary external magnetic field conditions. The rotational angular velocity is calculated by measuring the Larmor frequency of the nuclear spin and the electron spin of two closely adjacent NV center sets in diamond, which can suppress the influence of external magnetic field fluctuations on the rotational angular velocity measured by the gyroscope.

[0004] To achieve the above object, the present invention proposes a gyroscope based on NV center in diamond, comprising: a diamond plate having NV center and selected crystal axis; two wavelengths of 450nm

[0005] A 650nm light source is used to illuminate the diamond plate and form two independent NV center sets within the volume of the diamond plate in the irradiation area; a first optical system is capable of guiding the light from the light source to the diamond plate, and the light radiation power density can convert the spin projection of the electron spin system of the color center in the axial direction of the NV center to zero by continuously irradiating the diamond plate; a photodetector is capable of detecting the total fluorescence intensity of the NV center in the diamond plate; a second optical system is capable of guiding the fluorescence of the diamond plate to the photodetector; at least one ultra-high frequency microwave radiation source; at least one high frequency radiation source; a constant magnetic field source; and a control circuit is capable of generating control signals to control the microwave radiation source and the high frequency radiation source, the amplitude and frequency of the microwave radiation source and the high frequency radiation source, and the analog-to-digital conversion of the signals of the light source and the photodetector. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The present invention is illustrated by the following drawings.

[0007] Figure 1 Shown is an NV centre in diamond.

[0008] Figure 2 A block diagram of the device is shown, and its figure numbers are as described later. The first optical system includes elements 7 and 12, the second optical system includes elements 14 and 15, the microwave radiation source includes elements 17 and 18, and the constant magnetic field source includes elements 21 and 22. The constant magnetic field source may also include a permanent magnet to reduce the current in the Helmholtz coil, thereby saving energy consumption of the gyroscope. The constant magnetic field source may include a shielding layer to improve the stability of the generated magnetic field, and at least element 22 and the diamond plate are located in the shielding layer.

[0009] Figure 3 A schematic diagram of the ground state energy level sublevels of an NV centre is shown (not to scale).

[0010] 1: Diamond plate

[0011] 2.3: Light source

[0012] 4: Light used to illuminate the diamond plate

[0013] 5, 6: NV center collection

[0014] 7, 10: Photodetector to record light intensity

[0015] 8, 11: Beam splitter

[0016] 9, 12: Focusing lens

[0017] 13: Photodetector for fluorescence detection

[0018] 14: Parabolic concentrator for collecting fluorescence

[0019] 15: Filter

[0020] 16: Fluorescence emission

[0021] 17: Microwave generator

[0022] 18: Microwave Antenna

[0023] 19: High frequency generator

[0024] 20: High frequency antenna

[0025] 21: Current Source

[0026] 22: Helmholtz coil

[0027] 23: Control circuit DETAILED DESCRIPTION

[0028] In order to realize the gyroscope design of the present invention (such as Figure 2 As shown in Figure 1, a diamond plate with an NV center concentration in the range of 0.011000 ppm (parts per million) and a nitrogen concentration not exceeding 100 times the NV center concentration can be used, and other impurity concentrations are less than 1 ppm. Diamond plates with lower concentrations may result in insufficient fluorescence intensity, while diamond plates with higher concentrations may result in increased magnetic resonance width and decreased device sensitivity.

[0029] To achieve the technical effect and ensure measurement accuracy, two optical systems are used in the gyroscope.

[0030] The first optical system is used to guide the light from the light source to the diamond plate.

[0031] When light in the 650nm range is irradiated from two light sources onto the diamond plate, two independent NV center sets are formed within the volume of the diamond plate in the irradiated area. The first optical system is used to independently irradiate each NV center set with light, in order to convert the spin projection of the electron spin system of the NV center on the axis of the NV center to zero and to excite the fluorescence of the NV center. Appropriate LEDs and / or laser diodes can be used as light sources with a wavelength in the range of 450-650nm, and the system can include, for example, elements for focusing and directing the light into the volume of the diamond plate to ensure that the light radiation power density is at least 0.0001W / mm 2 . For example, biconvex lenses, parabolic mirrors and optical waveguides can be used as elements for focusing and guiding light. If the light source is close to the diamond plate, the focusing element can be omitted. In addition, to improve the measurement accuracy, the first optical system can use a beam splitter and its corresponding photodetector for each light source, receive an appropriate portion of the light radiation from the beam splitter, and normalize the fluorescence intensity of the NV center during the operation of the gyroscope. A silicon photodiode can be used as a photodetector.

[0032] The second optical system is used to collect fluorescent radiation with an efficiency of more than 1%. The optical elements of the second system collect and guide the fluorescent radiation in the diamond plate with a wavelength in the range of 650-800 nm (fluorescence spectrum of NV center) to the photodetector, while preventing the light of the first system with a wavelength less than 650 nm from entering the photodetector. The radiation can be filtered using a filter (e.g. Edmund Optics (USA) #34-742).

[0033] The photodetector is used to measure the total fluorescence intensity of the NV center in the diamond plate. A silicon photodetector can be used as a photodetector to convert the fluorescence intensity into a photocurrent, which can be converted into a voltage through a resistor or a transimpedance amplifier for analog-to-digital conversion. For example, Thorlabs (USA) model PDAl00A2 can be used as a combination of a photodetector and an amplifier.

[0034] An ultra-high frequency (microwave) radiation source with a frequency range of 15 GHz is used to excite magnetic dipole transitions of electron spin projection changes in the NV center collection. The radiation source consists of a sinusoidal signal generator and a resonator or antenna, the latter of which generates an alternating magnetic field in the collection area, and the amplitude of the magnetic field induction intensity in the orthogonal direction of the selected crystal axis is at least 0.001 Gs (Gauss). The signal from the generator can be further amplified by a power amplifier. As a generator, a frequency multiplier with fractional coefficients and capable of controlling the signal amplitude (such as Analog Devices (USA) model ADDF4351) can be used, which can be controlled by a modulation key (such as Minicircuits (USA) HSWA2-63DR+) or a direct digital synthesizer controlled by a digital signal. By using a microwave radiation source, magnetic dipole transitions between sub-energy levels with different quantum numbers mS can be excited (such as Figure 3 There may be multiple such radiation sources, for example one for each collection.

[0035] The constant magnetic field source is used to eliminate the degeneracy between the NV center magnetic dipole transition frequencies. As a constant magnetic field source, a source that provides a magnetic field induction intensity range of 0100 Gauss in the area occupied by the NV center set can be used. To ensure the effectiveness of the magnetic field fluctuation compensation algorithm, the difference in average magnetic field induction intensity between two NV center sets does not exceed 1 Gauss. For the overall operation of the gyroscope, the standard deviation of the magnetic field induction intensity within the volume of each NV center set does not exceed 1 Gauss to prevent non-uniform broadening of NV center transitions.

[0036] A high frequency (HF) radiation source with a frequency range up to 10 MHz is used to excite the hyperfine transitions of the NV center. Exciting the hyperfine transitions is required to measure the Larmor precession frequency of the nuclear spin, which is required to measure the angular velocity of rotation. A direct digital synthesis generator (e.g., Analog Devices (USA) AD9833) combined with a high power amplifier (e.g., Minicircuits (USA) LZY-22+) and a coil-shaped antenna can be used as a high frequency radiation source. In order to simultaneously generate high frequency signals of two frequencies (as described in step 4 below), the high frequency radiation source can include two digital synthesizers, whose signals are combined before being input to the amplifier. There can be multiple such high frequency radiation sources, for example, one for each set.

[0037] The control circuit is used to generate control signals to control the microwave and high frequency radiation sources, their amplitude and frequency, the light source, and the analog-to-digital conversion of the signals of the photodetector. A programmable logic integrated circuit (such as the Spartan7 series manufactured by Xilinx), a digital signal processing processor or a dedicated integrated circuit can be used as the control circuit to implement the algorithm of the following device. In addition, the control circuit includes an analog-to-digital converter and may also include a digital-to-analog converter to generate an analog control signal.

[0038] The working principle of the device is as follows.

[0039] Based on the effect of the change in the Larmor spin precession frequency when measuring in a rotating reference frame, the projection of the rotational angular velocity of the measuring device on z (Ω z ). However, the Larmor precession frequency (Ω L ) also depends on the induction strength (B) of the magnetic field in which the spin (with gyromagnetic ratio Y) is located.

[0040] Ω L =|γB z +Ω Z | (1)

[0041] Here, the z axis is the selected crystal axis in diamond. Here, the following fact is used: under the condition of magnetic field less than 100 Gauss, the z axis can be regarded as the quantization axis of electron spin and nuclear spin, because for the corresponding spin, the Zeeman interaction is mainly dominated by the spin-spin interaction and the quadrupole interaction of the lattice field. In order to remove the magnetic field B from expression (1), Z The fluctuation component of is measured using the Larmor frequencies of two different spins.

[0042] In the present invention, one set uses nuclear spin (subscript n) and the other set uses electron spin (subscript e). Using expression (1), in |Ω z |<<|γB z| Under the condition of n and Ω e ,available:

[0043]

[0044] Among them, Ye and γn are the gyromagnetic ratios of the NV center electron spin and the nitrogen nuclear spin, respectively.

[0045] The Larmor frequencies of nuclear and electron spins must be measured simultaneously, otherwise the efficiency of compensation of magnetic field fluctuations will be reduced due to stroboscopic effects.

[0046] The Larmor frequency of the nuclear spin (Ω n ) is measured by performing the following steps 1 to 7, the Larmor frequency (Ω) of the electron spin e ) is measured by performing the following steps 8 to 18.

[0047] 1. By the following operations a, b and c, the state of the first NV center set in the diamond plate is set to |mS=0, mI=-0> (where mS and mI are the projections of the electron spin and nuclear spin on the z-axis, respectively).

[0048] a. Illuminate the first set with a light source to set the electron spin state of the NV center set to mS = 0. The pulse duration is typically in the range of 1 to 1000 microseconds.

[0049] b. Irradiate the diamond plate using the following pulse sequence.

[0050] i. Microwave π pulse, transition frequency is F5

[0051] ii. Microwave π pulse, transition frequency is F6

[0052] iii. Low frequency π pulse, transition frequency is F10

[0053] iv. Low frequency π pulse, transition frequency is F11

[0054] As a result, the population distribution between the hyperfine and electronic magnetic sublevels is exchanged, filling the first set with the hyperfine sublevel mI=0.

[0055] C. Then use a light source to illuminate the first set, transferring its state to |mS=0, mI=0>.

[0056] 2. Then, using a high-frequency radiation source, two π pulses are applied simultaneously at transition frequencies F8 and F9 with a duration of T7 to transfer the first set to a superposition state.

[0057] 1 / 2^(1 / 2)(|mS=0,mI=+1>+e^(1j*φ 0)|mS=0,mI=-1>) (3)

[0058] 3. After that, if no operation is performed on the set within time T, the state of the set becomes 2^(1 / 2)(e^(1j*(φ 0 -φ))|mS=0,mI=+1>+e^(1j*(φ 0 +φ))|mS=0, mI=-1>), where φ=TΩ n The dynamic phase.

[0059] 4. Then, a high-frequency radiation source is used to simultaneously apply π pulses at transition frequencies F8 and F9 with a duration of T7.

[0060] 5. Then, apply 5 pulses at frequency F7 using a microwave radiation source.

[0061] 6. Then, the first set is illuminated using a light source and the fluorescence intensity is measured (S1).

[0062] 7. Calculate the Larmor frequency Ω by the following formula n .

[0063]

[0064] To determine Ω n , choose time T = Tm so that for a certain Larmor frequency Ω n0 Meet 2Ω n0 (Tm+2*T7)+φ′=2πN, where N is an integer.

[0065] A, B, φ′, and T2* are empirical coefficients that can be determined by repeating steps 1 to 7 for different times T under constant magnetic field and no rotation conditions and using the fitting formula (5).

[0066] S1=A+B*sin(2Ω n (T+2*T7)+φ′)*exp(-T / T2*) (5)

[0067] In the second set, the Larmor frequency Ω of the electron spin is measured e .

[0068] The Larmor precession frequency can be calculated by the difference between the NV center magnetic transition frequencies F12 and F7.

[0069] Ω e =(F12-F7) / 2 (6)

[0070] Frequencies F12 and F7 can be determined by pulsed or continuous optical detection magnetic resonance (ODMR) methods, i.e., the NV center is probed in a microwave field slightly deviated (1 to 1000 kHz) from the transition frequencies (F1, F2, F3, F4). Taking continuous optical detection resonance as an example, the measurement steps of the precession frequency are as follows.

[0071] 8. Use the light source to illuminate the second set and set its state to mS=0.

[0072] 9. Use a microwave radiation source to apply π pulses at a frequency of F1.

[0073] 10. Use the light source to illuminate the second set for a duration of T2O, and detect the fluorescence intensity S1.

[0074] 11. Use a microwave radiation source to apply π pulses at a frequency of F2.

[0075] 12. Use the light source to illuminate the second set for a duration of T20, and detect the fluorescence intensity S2.

[0076] 13. Use a microwave radiation source to apply π pulses at a frequency of F3.

[0077] 14. Use the light source to illuminate the second set for a duration of T20, and detect the fluorescence intensity S3.

[0078] 15. Use a microwave radiation source to apply π pulses at a frequency of F4.

[0079] 16. Use the light source to illuminate the second set for a duration of T20, and detect the fluorescence intensity S4.

[0080] 17. Calculate the frequencies F12 and F7 using the following formula.

[0081] F7'=(S2-S1)*A7 (7)

[0082] F12'=(S4-S3)*A12 (8)

[0083] 18. Calculate the Larmor precession frequency of electron spin using the following formula.

[0084] Ω e =(F12′-F7′) / 2

[0085] The coefficients A7 and A12 are determined by calibration experiments, that is, steps 7 to 14 are repeated while adjusting the frequency pairs F1, F2 and F3, F4.

[0086] The duration of the π pulses should be the same in steps 7, 9, 11, and 13. The duration and frequency adjustments (F2-F1) and (F3-F4) should be selected to make coefficients A7 and A12 as small as possible to improve the detection sensitivity of F7 and F12.

[0087] In the device algorithm, the order of the frequency measurements in steps 8 to 16 can be changed, and the number of polling times can also be changed to ensure that the total number of polling times for each frequency is the same.

[0088] When measuring the Larmor precession frequency of the electron spin through steps 8 to 18 and the Larmor precession frequency of the nuclear spin through steps 1 to 7, it is necessary to ensure that the start time of step 9 is synchronized with the start time of step 2, and the end time of the π pulse in step 4 is synchronized with the end time of step 13. To this end, the fluorescence accumulation time T20 and the polling times of the frequencies F1, F2, F3, and F4 need to be appropriately selected.

[0089] The presence of magnetic field differences between sets may lead to systematic errors. To eliminate this error, the rotational angular velocity can be averaged by making an even number of measurements; periodically reallocating the set numbers, i.e., reallocating the first set to the second set (performing steps 8 to 18 on it), and reallocating the second set to the first set (performing steps 1 to 7 on it); and then restoring the numbers.

Claims

1. A gyroscope based on NV centers in diamond, comprising: a diamond plate having NV centers and a selected crystal axis; two light sources with wavelengths ranging from 450 nm to 650 nm, irradiating the diamond plate and forming two independent NV center assemblies within the volume of the diamond plate in the irradiation area; a first optical system capable of guiding the light from the light sources to the diamond plate, and the optical radiation power density can convert the spin projection of the electron spin system of the color center along the NV center axis to zero through continuous irradiation of the diamond plate; a light detector capable of detecting the total fluorescence intensity of the NV centers in the diamond plate; a second optical system capable of guiding the fluorescence of the diamond plate to the light detector; at least one ultra-high frequency microwave radiation source; at least one high frequency radiation source; a constant magnetic field source; and a control circuit capable of generating control signals to control the microwave radiation source and the high frequency radiation source, the amplitude and frequency of the microwave radiation source and the high frequency radiation source, and the analog-to-digital conversion of the signals of the light sources and the light detector.

2. The gyroscope based on NV centers in diamond according to claim 1, wherein, the constant magnetic field source is used to generate a magnetic field with a magnetic induction intensity ranging from 0 to 100 Gauss in the area where the NV center assemblies are located, and the standard deviation within the volume of each NV center assembly does not exceed 1 Gauss.

3. The gyroscope based on NV centers in diamond according to claim 1, wherein, the constant magnetic field source can maintain a constant magnetic field in the areas of the two NV center assemblies in the diamond plate.

4. The gyroscope based on NV centers in diamond according to claim 1, wherein, the constant magnetic field source can maintain the difference in the average magnetic induction intensity between the two NV center assemblies not exceeding 1 Gauss.

5. The gyroscope based on NV centers in diamond according to claim 1, wherein, the constant magnetic field source can maintain a constant magnetic field in the entire area of the diamond plate.

6. The gyroscope based on NV centers in diamond according to claim 1, wherein, the first optical system also uses a beam splitter and a corresponding light detector for each light source, so as to normalize the fluorescence intensity of the NV centers during the operation of the gyroscope.

7. The gyroscope based on NV centers in diamond according to claim 1, wherein, the concentration range of NV centers in the diamond plate is 0.01 to 1000 ppm, the nitrogen concentration does not exceed 100 times the NV center concentration, and the concentration of other impurities is less than 100 ppm.

8. The gyroscope based on NV centers in diamond according to claim 1, wherein, using a laser or LED light source with a power of at least 0.01 W, the first optical system can generate an optical radiation power density of at least 0.0001 W / mm2.

9. The gyroscope based on NV centers in diamond according to claim 1, wherein, using an ultra-high frequency microwave radiation source with a frequency range of 1 to 5 GHz.

10. The gyroscope based on NV centers in diamond according to claim 1, wherein, The frequency range of the microwave radiation source is from 1 to 5 GHz, and it also includes an antenna, capable of generating an alternating magnetic field with a magnetic induction intensity of at least 0.001 gauss in the orthogonal direction of the selected crystal axis.

11. The gyroscope based on the NV center in diamond according to claim 1, characterized in that, a high-frequency radiation source with a frequency up to 10 MHz is used.

12. The gyroscope based on the NV center in diamond according to claim 1, characterized in that, the fluorescence radiation collection efficiency of the second optical system is higher than 1%.

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