A frequency agile method based on FPGA control

Abstract

The application discloses a frequency agile method and module based on FPGA control and a quantum sensing system, inputs a clock signal f_1 generated by a constant temperature crystal oscillator into a PLL, inputs a high frequency clock signal f_2 output by the PLL based on input reference signal frequency multiplication into a clock input end of a DDS chip, calculates a frequency control word M based on a frequency control instruction FTW through FPGA, and writes the frequency control word M in binary form into a register corresponding to an n-bit phase accumulator of the DDS chip through a high-speed IO port, and outputs a microwave frequency adjustment signal f_3 according to the clock signal f_2 and the frequency control word M. The FPGA is used as a control core of a frequency source output signal by taking advantages of flexibility and high calculation efficiency, and can complete frequency hopping output in a time scale of ns. In addition, compared with a finished microwave source, the structure is relatively simple, and the hardware cost is greatly reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of quantum sensing technology, and particularly relates to a frequency agility method based on FPGA control. BACKGROUND

[0002] Quantum sensing systems include cold atoms, ion traps, atomic vapors, superconducting circuits, and solid-state spins, among which diamond NV color centers are one of the solid-state quantum spin systems, have excellent optical readout, polarization properties, and very short coherence time, and unlike other quantum sensing systems, the diamond NV color center solid-state quantum sensing system can achieve high-sensitivity measurement at room temperature, which has great potential in industrial applications. Especially in the field of electric power measurement, the reliable operation of the power system and the real-time state detection of the electrical equipment cannot be separated from the accurate and real-time acquisition of voltage and current information. The diamond NV color center quantum sensor sensitive to electric and magnetic fields is a hot spot of researchers.

[0003] The diamond NV color center is a structure in which a carbon atom in the diamond structure is replaced by a nitrogen atom, and the adjacent place is a hole structure, which has C_3v symmetry. The ground state and the excited state of the diamond NV color center are both triplet states, which are M_s=0, M_s=±1 three states, among which the +1 and-1 states are degenerate states without the action of a magnetic field. When a magnetic field is applied, the degenerate states will separate, and the degree of separation is linearly related to the size of the magnetic field. The energy corresponding to the wavelength of the ground state and the excited state of the diamond NV color center is 637nm, when the wavelength of the laser used to irradiate the NV color center is less than 637nm, the electron on the ground state of the NV color center will absorb energy and transition to the excited state. The electron on the excited state is unstable and will undergo transition. However, not all electrons on the M_s=±1 state return to the original route, a part of the electrons will return to the ground state through non-radiative transition, and this process does not emit light. Therefore, for the diamond NV color center, the transition between the ground state and the excited state is conserved, but the transition through the metastable state, i.e. non-radiative transition, is not conserved, so the more electrons participating in non-radiative transition, the greater the probability of non-radiative transition, and the weaker the fluorescence emitted by the NV color center. The strength of the fluorescence can be used to judge the electron spin state of the NV color center. When the intensity of the fluorescence stabilizes, the complete polarization of the laser to the NV color center is completed. At this time, when the frequency of the microwave applied to the NV color center is equal to the energy level difference of the electron spin of the NV color center, resonance occurs, and the resonant microwave makes the electron of the NV color center transition from the 0 state to the +1 state or the-1 state, resulting in a decrease in fluorescence counting. Therefore, by applying continuous laser and microwave to the diamond NV color center, an optical detection magnetic resonance spectrum can be obtained. When a magnetic field exists, the energy level difference of the +1 state and the-1 state will increase due to the degenration of the energy level difference, and the two resonance peaks of the optical detection magnetic resonance spectrum will also move away from each other, and the frequency difference corresponding to the trough of the two resonance peaks is linearly related to the magnetic field strength, which can be specifically seen from the following formula:

[0004] Delta f = 2 * gamma * B

[0005] Wherein, Delta f is the difference between the microwave frequency at the wave peak and wave trough of the optical detection magnetic resonance spectrum, gamma is the gyromagnetic ratio, gamma is approximately 2.8MHz / Gs, B is the magnetic field strength around the NV color center. Since the zero field splitting value of the diamond NV color center is 2.87GHz, a pair of wave peaks presents a symmetrical relationship on the optical detection magnetic resonance spectrum, and the microwave resonance frequency f corresponding to the wave trough of the wave peak satisfies the following formula:

[0006] F = 2.87GHz + gamma * B

[0007] Therefore, the measurement of the size of the magnetic field by using the diamond NV color center can be converted into the measurement of the size of the microwave resonance frequency. In practical application, when the microwave source is continuously swept in a suitable frequency domain, the smaller the sweep step is, the higher the accuracy of the obtained spectrum is. However, in a suitable region, a complete sweep needs to experience several hundred or even thousands of frequency jumps to obtain a complete measurement spectrum, and the time interval for completing the measurement of the magnetic field each time is large, which leads to that the sampling rate of the measurement system cannot meet the requirement of the mutual inductor in the power system, and the diamond NV color center quantum sensing system cannot be applied to the actual scene of the power measurement in the basic index. Based on this background, in order to reduce the time for one measurement and improve the sampling rate of the system, the key is to find the size of the microwave resonance frequency in a short time. SUMMARY

[0008] In order to solve the technical problems in the background art, the application provides a frequency agile method based on FPGA control, a module and a quantum sensing system.

[0009] The frequency agile method based on FPGA control provided by the application comprises the following steps:

[0010] S1, inputting a clock signal f_1 generated by a constant temperature crystal oscillator into a PLL (phase-locked loop) as an input reference signal of the PLL;

[0011] S2, inputting a high-frequency clock signal f_2 output by frequency multiplication of the input reference signal of the PLL into a clock input end of a DDS (direct digital frequency synthesizer) chip as a clock reference signal of the DDS chip;

[0012] S3, calculating a frequency control word M based on a frequency control instruction FTW by using the FPGA, and writing the frequency control word M in the form of binary into a register corresponding to an n-bit phase accumulator of the DDS chip through a high-speed IO port;

[0013] S4, the DDS chip outputs a microwave frequency adjustment signal f_3 according to the clock signal f_2 and the frequency control word M.

[0014] Preferably, in S3, the signal f_3 is filtered through a low-pass filter to filter out high harmonics and image frequencies to obtain a signal f_4.

[0015] Preferably, in S3, the filtered signal f_4 is amplified by a power amplifier.

[0016] Preferably, in S4, the microwave adjustment frequency signal f_3 is obtained by the following equation:

[0017]

[0018] In the formula, f_3 is the signal output by the DDS chip, M is the frequency control word, n is the bit width of the phase accumulator of the DDS chip, and f_time is the input reference clock signal of the DDS chip.

[0019] In the present application, the proposed frequency agile method based on FPGA control inputs the clock signal f_1 generated by the constant temperature crystal oscillator into the PLL, inputs the high frequency clock signal f_2 output by the PLL based on the input reference signal frequency multiplication into the clock input end of the DDS chip, calculates the frequency control word M based on the frequency control instruction FTW through the FPGA, and writes the frequency control word M in binary form into the corresponding register of the n-bit phase accumulator of the DDS chip through the high-speed IO port; the DDS chip outputs a microwave frequency adjustment signal f_3 according to the clock signal f_2 and the frequency control word M. By using the advantages of flexibility and high computing efficiency of FPGA, the FPGA is used as the control core of the frequency source output signal, and the frequency jump output can be completed within the time scale of ns. In addition, compared with the finished microwave source, the structure is relatively simple, and the hardware cost is greatly reduced.

[0020] The present application also proposes a frequency agile module based on FPGA control for realizing the above-mentioned frequency agile method based on FPGA control.

[0021] The frequency agile module comprises a receiving control unit, a PLL unit and a DDS chip, the receiving control unit is used for converting the control instruction FTW based on the magnetic field detection signal into a frequency control word, the PLL unit is used for providing a reference clock, and the DDS chip is used for outputting a microwave frequency adjustment signal according to the frequency control word and the reference clock.

[0022] Preferably, the frequency agile module further comprises a microwave amplification unit, and the microwave amplification unit is used for power amplifying the microwave signal output by the DDS chip.

[0023] Preferably, the frequency agile module further comprises a circulator for preventing the backflow of the high-frequency microwave signal.

[0024] The application further provides a frequency agile tracking quantum sensing system, comprising an excitation module, a sensing module, a signal processing module and the frequency agile module described above.

[0025] The sensing module comprises a diamond NV color center sample and a microwave antenna, the excitation module is configured to emit laser to the diamond NV color center sample, the microwave antenna is configured to apply a magnetic field to the diamond NV color center sample, and the diamond NV color center sample is configured to obtain a magnetic field detection signal.

[0026] The signal processing module comprises a digital phase-locked unit, a frequency calculation unit and an interactive transmission unit, the digital phase-locked unit is configured to extract and demodulate the magnetic field detection signal by the digital phase-locked unit, the frequency calculation unit is configured to calculate the difference AV between the real-time signal demodulation amplitude V_1 of the digital phase-locked unit and the locking amplitude V_0, and calculate the resonance frequency deviation Δf according to the conversion coefficient k between the demodulation amplitude and the microwave frequency, and the interactive transmission unit is configured to convert the frequency deviation Δf into a control instruction FTW.

[0027] Preferably, the frequency agile module further comprises a host computer module, the host computer module is configured to display the frequency deviation value Δf and the magnetic field strength obtained by the signal processing module in real time.

[0028] Preferably, the frequency agile module further comprises a host computer module, the host computer module is configured to control the frequency agile module to perform frequency sweeping, obtain an optical detection magnetic resonance (ODMR) spectrum line, and lock the microwave resonance frequency and the signal demodulation amplitude at the frequency.

[0029] In the application, the frequency agile module and the frequency agile tracking quantum sensing system based on FPGA control have similar technical effects to the frequency agile method described above, and thus will not be described again. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 FIG. 1 is a structural schematic diagram of an embodiment of the frequency agile module based on FPGA control according to the application.

[0031] Figure 2 FIG. 3 is a schematic diagram of the communication connection between the FPGA host and the DDS chip in an embodiment of the frequency agile module based on FPGA control according to the application.

[0032] Figure 3 FIG. 5 is a connection block diagram of an embodiment of the frequency agile tracking quantum sensing system according to the application.

[0033] Figure 4A schematic diagram of an optical path of a sensing module in an embodiment of the frequency agile tracking quantum sensing system according to the present application.

[0034] Figure 5 A connection block diagram of a signal processing module in an embodiment of the frequency agile tracking quantum sensing system according to the present application. DETAILED DESCRIPTION

[0035] As shown in Figures 1 to 5 , Figure 1 A structural schematic diagram of an embodiment of the frequency agile module based on FPGA control according to the present application, Figure 2 A communication connection schematic diagram of an FPGA host and a DDS chip in an embodiment of the frequency agile module based on FPGA control according to the present application, Figure 3 A connection block diagram of an embodiment of the frequency agile tracking quantum sensing system according to the present application, Figure 4 A schematic diagram of an optical path of a sensing module in an embodiment of the frequency agile tracking quantum sensing system according to the present application, Figure 5 A connection block diagram of a signal processing module in an embodiment of the frequency agile tracking quantum sensing system according to the present application.

[0036] The present application provides a frequency agile method based on FPGA control, comprising the following steps:

[0037] S1, inputting a clock signal f_1 generated by a constant temperature crystal oscillator into a PLL 16 as an input reference signal of the PLL 16;

[0038] S2, inputting a high-frequency clock signal f_2 output by frequency multiplication of the input reference signal of the PLL 16 into a clock input end of a DDS chip as a clock reference signal of the DDS chip;

[0039] S3, calculating a frequency control word M based on a frequency control instruction FTW through an FPGA, and writing the frequency control word M in the form of binary into a register corresponding to an n-bit phase accumulator of the DDS chip through a high-speed IO port;

[0040] S4, outputting a microwave frequency adjustment signal f_3 according to the clock signal f_2 and the frequency control word M by the DDS chip.

[0041] In order to describe the frequency agile method based on FPGA control of the present embodiment in detail, refer to Figures 1-5 The present embodiment also provides a frequency agile tracking quantum sensing system, comprising an excitation module 1, a sensing module 2, a signal processing module 4 and a frequency agile module 6.

[0042] The sensing module 2 comprises a diamond NV color center sample 9 and a microwave antenna 10, the excitation module 1 is used for emitting laser to the diamond NV color center sample 9, the microwave antenna 10 is used for acting on the diamond NV color center sample 9 with a magnetic field, and the diamond NV color center sample 9 is used for acquiring a magnetic field detection signal;

[0043] Specifically, the sensing module 2 further comprises a dichroic mirror 7 and a confocal objective lens 8; the laser emitted by the excitation module 1 is reflected by the dichroic mirror 7 to the confocal objective lens 8, and then irradiates the diamond NV color center sample 9, and the excitation fluorescence of the diamond NV color center sample 9 is emitted in turn through the confocal objective lens 8 and the dichroic mirror 7. The dichroic mirror is inclined by 45°, reflects 532nm laser, and transmits 600-800nm waveband fluorescence, the confocal objective lens focuses the 532nm laser reflected by the dichroic mirror, the diamond NV color center sample is a block solid containing a certain concentration of diamond NV color centers, the microwave antenna converts a microwave radio frequency signal into a high-quality alternating magnetic field to act on the diamond NV color center, and the diamond NV color center sample emits 600-800nm waveband red fluorescence under the excitation of the 532nm laser, which is collected by the confocal objective lens and then transmitted out through the dichroic mirror.

[0044] The signal processing module 4 comprises a digital phase-locked unit 12, a frequency calculation unit 13 and an interactive transmission unit 14, the digital phase-locked unit 12 is used for extracting and demodulating the magnetic field detection signal through the digital phase-locked unit 12, the frequency calculation unit 13 is used for calculating the difference AV between the real-time signal demodulation amplitude V_1 of the digital phase-locked unit 12 and the locking amplitude V_0, and calculating the resonance frequency deviation Af according to the conversion coefficient k of the demodulation amplitude and the microwave frequency, and the interactive transmission unit 14 is used for converting the frequency deviation Af into a control instruction FTW;

[0045] The frequency agile module 6 comprises an FPGA host, a PLL 16 and a DDS chip 17, the FPGA host comprises a control word calculation unit and a control unit, the control word calculation unit is used for converting the control instruction FTW based on the magnetic field detection signal into a frequency control word, the control unit is used for realizing rapid transmission and writing of the calculated frequency control word M through high-speed SPI communication, the PLL 16 is used for providing a reference clock, and the DDS chip 17 is used for outputting a microwave frequency adjustment signal according to the frequency control word and the reference clock.

[0046] Wherein, the FPGA development board as the host, module board card containing DDS chip as the slave, two module board cards are connected through high-speed IO port. FPGA development board mainly has two parts, respectively for control word calculation unit and control unit, wherein the control word calculation unit completes the calculation of frequency control word M, the control unit is responsible for the calculated frequency control word M through high-speed SPI communication to realize fast transmission and write, the transmission rate of 100 megabit level SPI and the clock of GHz level register loading, can in dozens to hundreds of ns time scale, the binary frequency control word is transmitted from the FPGA end to write to the corresponding register of DDS chip, so as to complete the ns level frequency agile.

[0047] In the specific working process of the diamond NV color center based frequency agile tracking quantum sensing system of the embodiment, the microwave antenna converts the microwave radio frequency signal into a high-quality alternating magnetic field acting on the diamond NV color center, and the diamond NV color center sample emits fluorescence under the excitation of the laser;

[0048] The fluorescence signal is converted and extracted and demodulated by the digital phase-locked unit, then the difference AV between the real-time signal demodulation amplitude V_1 and the locking amplitude V_0 of the digital phase-locked unit is calculated by the frequency calculation unit 13, and the resonance frequency deviation Af is calculated according to the conversion coefficient k of the demodulation amplitude and the microwave frequency, and the frequency deviation Af is converted into a control instruction FTW through the interactive transmission unit 14;

[0049] The FPGA host converts the control instruction FTW into a frequency control word, and the DDS chip 17 outputs a microwave source frequency adjustment signal according to the frequency control word and the reference clock provided by the PLL 16, so as to realize the frequency agile tracking of the diamond NV color center.

[0050] In the embodiment, the proposed frequency agile method based on FPGA control inputs the clock signal f_1 generated by the constant temperature crystal oscillator into the PLL, inputs the high frequency clock signal f_2 output by the PLL based on the input reference signal frequency multiplication into the clock input end of the DDS chip, calculates the frequency control word M based on the frequency control instruction FTW through the FPGA, and writes the frequency control word M in binary form into the register corresponding to the n-bit phase accumulator of the DDS chip through the high-speed IO port; the DDS chip outputs a microwave frequency adjustment signal f_3 according to the clock signal f_2 and the frequency control word M. By using the advantages of flexibility and high calculation efficiency of FPGA, the FPGA is used as the control core of the frequency source output signal, and the frequency jump output can be completed in the time scale of ns. In addition, compared with the finished microwave source, the structure is relatively simple, and the hardware cost is greatly reduced.

[0051] In the S4, the microwave adjustment frequency signal f_3 is obtained by the following equation:

[0052]

[0053] In the formula, f_3 is the signal output by the DDS chip, M is the frequency control word, n is the bit width of the phase accumulator of the DDS chip, and f_time is the input reference clock signal of the DDS chip.

[0054] The spurs of the microwave frequency adjustment signal f_3 can be filtered before output, that is, in S3, the signal f_3 is passed through a low-pass filter to filter out high-order harmonics and image frequencies to obtain a signal f_4. Further, the filtered signal f_4 is amplified by a power amplifier. Accordingly, in the specific design of the frequency agile module, the frequency agile module further includes a microwave amplification unit for power amplifying the microwave signal output by the DDS chip 17.

[0055] In addition, the frequency agile module 6 further includes a circulator for preventing backflow of high-frequency microwave signals.

[0056] In other specific embodiments of the frequency agile tracking quantum sensing system of the present embodiment, a host computer module 5 is further included, which is used to display the frequency deviation value Δf and the magnetic field strength obtained by the signal processing module 4 in real time. The host computer module 5 can also be used to control the frequency agile module 6 to sweep the frequency to obtain the optical detection magnetic resonance (ODMR) spectrum, and lock the microwave resonance frequency and the signal demodulation amplitude at the frequency.

[0057] In addition, the quantum sensing system of the present embodiment can further include a fluorescence collection unit 3 for converting the excitation fluorescence signal of the diamond NV center sample 9 into an electrical signal. Specifically, the fluorescence collection unit 3 includes a filter set for filtering out light of non-target wavebands and a photodetector for converting the fluorescence signal into an electrical signal.

[0058] The above description is only a preferred embodiment of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can make equivalent replacements or changes to the technical solution and the inventive concept of the present application within the technical scope disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A frequency agile method based on FPGA control, characterized in that, The method comprises the following steps: S1, inputting a clock signal f_1 generated by a constant temperature crystal oscillator into a PLL (16) as an input reference signal of the PLL (16); S2, inputting a high-frequency clock signal f_2 output by frequency multiplication of the input reference signal of the PLL (16) into a clock input end of a DDS chip as a clock reference signal of the DDS chip; S3, converting a control instruction FTW based on a magnetic field detection signal into a frequency control word M through an FPGA, and writing the frequency control word M in binary form into a register corresponding to an n-bit phase accumulator of the DDS chip through a high-speed IO port; S4, outputting a microwave frequency adjustment signal f_3 by the DDS chip according to the clock signal f_2 and the frequency control word M.

2. The FPGA control based frequency agility method of claim 1, wherein, In S3, the signal f_3 is filtered through a low-pass filter to filter out high-order harmonics and image frequencies to obtain a signal f_4.

3. The FPGA control based frequency agility method of claim 2, wherein, In S3, the filtered signal f_4 is amplified through a power amplifier.

4. The FPGA control based frequency agility method of claim 1, wherein, In S4, the microwave frequency adjustment signal f_3 is obtained by the following equation: In the formula, f_3 is a signal output by the DDS chip, M is a frequency control word, n is the bit width of the phase accumulator of the DDS chip, and f_time is an input reference clock signal of the DDS chip.

5. A frequency agile module based on FPGA control, characterized in that, The frequency agile method based on FPGA control is used to realize the method according to any one of claims 1-4; The frequency agile module (6) comprises an FPGA host (15), a PLL (16) and a DDS chip (17), the FPGA host comprises a control word calculation unit and a control unit, the control word calculation unit is used to convert a control instruction FTW based on a magnetic field detection signal into a frequency control word M, the control unit is used to realize fast transmission and writing of the calculated frequency control word M through high-speed SPI communication, the PLL (16) is used to provide a reference clock, and the DDS chip (17) is used to output a microwave frequency adjustment signal according to the frequency control word and the reference clock.

6. The FPGA control based frequency agile module of claim 5, wherein, The frequency agile module further comprises a microwave amplification unit (18), which is used to amplify the microwave signal output by the DDS chip (17).

7. The FPGA control based frequency agile module of claim 5, wherein, The frequency agile module (6) further comprises a circulator (19), which is used to prevent high-frequency microwave signals from flowing back.

8. A frequency agile tracking quantum sensing system, characterized by, The method comprises an excitation module (1), a sensing module (2), a signal processing module (4) and the frequency agile module (6) according to any one of claims 5-7; The sensing module (2) comprises a diamond NV color center sample (9) and a microwave antenna (10), the excitation module (1) is used to emit laser to the diamond NV color center sample (9), the microwave antenna (10) is used to act on a magnetic field of the diamond NV color center sample (9), and the diamond NV color center sample (9) is used to obtain a magnetic field detection signal; The signal processing module (4) includes a digital phase-locked unit (12), a frequency calculation unit (13), and an interactive transmission unit (14). The digital phase-locked unit (12) is used to extract and demodulate the magnetic field detection signal. The frequency calculation unit (13) is used to calculate the difference between the real-time signal demodulation amplitude V_1 and the locking amplitude V_0 of the digital phase-locked unit (12). V, and calculate the resonant frequency deviation based on the conversion coefficient k between the demodulation amplitude and the microwave frequency. f, the interactive transmission unit (14) is used to transmit the frequency deviation f is converted into the control command FTW; Further comprising a host computer module (5), the host computer module (5) is used to control the frequency agile module (6) to perform frequency sweeping to obtain an optical detection magnetic resonance (ODMR) spectrum line, and lock a microwave resonance frequency and a signal demodulation amplitude value at the frequency.

9. The frequency-agile tracking quantum sensing system of claim 8, wherein, The system further comprises a host computer module (5) for displaying the frequency deviation value obtained by the signal processing module (4) in real time f and the magnetic field strength.

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