CN108494494B - Method for locking single photon phase in real time - Google Patents

Method for locking single photon phase in real time Download PDF

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CN108494494B
CN108494494B CN201810261222.7A CN201810261222A CN108494494B CN 108494494 B CN108494494 B CN 108494494B CN 201810261222 A CN201810261222 A CN 201810261222A CN 108494494 B CN108494494 B CN 108494494B
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phase
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phi
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voltage
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CN108494494A (en
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于波
菅在河
张清
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Xinzhou Teachers University
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    • H—ELECTRICITY
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    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/50—Transmitters
    • H04B10/516—Details of coding or modulation
    • H04B10/548—Phase or frequency modulation
    • H04B10/556—Digital modulation, e.g. differential phase shift keying [DPSK] or frequency shift keying [FSK]
    • H04B10/5561—Digital phase modulation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/50—Transmitters
    • H04B10/516—Details of coding or modulation
    • H04B10/524—Pulse modulation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
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    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
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    • H04L9/08—Key distribution or management, e.g. generation, sharing or updating, of cryptographic keys or passwords
    • H04L9/0816—Key establishment, i.e. cryptographic processes or cryptographic protocols whereby a shared secret becomes available to two or more parties, for subsequent use
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Abstract

The invention relates to a method for locking relative phases of two single photon light fields in real time based on a phase estimation algorithm and a search algorithm by utilizing a single photon interference method and a single photon counting method. The relative phase of the two single photon light fields is converted into the physically measurable intensity by using a single photon interference method, and the statistical value of the single photon intensity is measured by using a single photon counting method, so that the measurement of the relative phase of the two single photon light fields is realized. And comparing the measured relative phase with a set reference phase, calculating the optimized phase adjusting voltage by using a phase estimation algorithm when the deviation between the measured relative phase and the set reference phase is large so as to quickly perform phase feedback, calculating the optimized phase adjusting voltage by using a search algorithm when the deviation between the measured relative phase and the set reference phase is small, and locking the relative phases of the two single photon light fields by continuously repeating the steps. The method can be applied to locking the phase of the single photon signal in the phase coding quantum key distribution system, and has the advantages of simple operation, high locking efficiency and high precision.

Description

Method for locking single photon phase in real time
Technical Field
The invention belongs to the field of quantum communication, and particularly relates to a method for locking a single photon phase in real time based on single photon phase interference and single photon counting.
Background
With the development of society, the secure communication technology will play more and more important roles in various fields such as military, finance, information and the like.
The quantum key distribution ensures the absolute security of the key by the physical principle, and the secure communication can be realized by combining the secure key with the one-time pad encryption mode, so the quantum key distribution is valued by various countries and develops rapidly. At present, quantum key distribution using a single photon as a carrier mainly uses polarization and phase of the single photon to load information. In single mode fiber, phase encoded quantum key distribution is typically performed in single mode fiber, since phase is easier to stabilize than polarization. However, in an actual environment, phase drift caused by environmental random disturbance affects the working stability of the phase-coded quantum key distribution system, and the working performance of the system is reduced. The two communication parties can obtain the phase drift parameters by scanning the interference intensity curve of the single photon signal by using a four-phase scanning method so as to compensate the phase drift of the single photon, but the method needs to scan 4 interference curves of the receiving party, is complex in operation, long in consumed time, limited in locking precision and not beneficial to practical application, and the two communication parties need to exchange information, so that the safety of the system is reduced.
Disclosure of Invention
In order to solve the existing problems, the invention provides a method for locking the relative phase of two single photon light fields in real time by using a single photon interference method and a single photon counting method based on a phase estimation algorithm and a search algorithm, which can be applied to the phase drift of a compensation system in a phase coding quantum key distribution system, improves the interference visibility of the single photon, and has the advantages of no need of information exchange between the two parts, simple operation, high locking efficiency and high precision.
The invention is realized by adopting the following technical scheme:
a method for locking single photon phase in real time comprises the following steps:
s1, marking the two single photon light fields as a reference light field and a signal light field respectively, wherein the phase of the signal light field can be adjusted, and the reference phase of the two light fields to be locked is set to be delta phir，Δφr∈[0，2π)。
And S2, measuring the relative phase delta phi between the two single photon optical fields.
The relative phase of the two single photon light fields is measured by converting the non-Hermite phase into Hermite intensity by a single photon interference method, and the measured intensity is measured by a single photon detection method and a single photon counting method. The single photon detector is used as a tool for measuring the single photon intensity in the single photon detection method. The single photon counting method is to count the digital pulses output by the single photon detector to obtain the intensity information of the light field. The method comprises the following specific steps:
the signal light field is input to the input end of the phase modulation module, the output end of the phase modulation module is connected to one input end of a 50:50 optical fiber coupler, the reference light field is input to two input ends of the optical fiber coupler, two single photon light fields meet in the optical fiber coupler to generate interference, the output end of the optical fiber coupler is connected to the input end of a single photon detector, the output end of the single photon detector is connected to the input end of a photon counting module, the output end of the photon counting module is connected to the input end of the phase calculation module, the output end of the phase calculation module is connected to the voltage input end of the phase modulation module, and the voltage of the voltage input.
The signal light field is coherent light field, and its annihilation operator is expressed as
Figure BDA0001610299990000021
The wave function is represented as | αsig>. The reference light field is coherent light field, and its annihilation operator is expressed as
Figure BDA0001610299990000031
The wave function is represented as | αref>. The signal light and the reference light have the same frequency and polarization direction, and the two beams of light are input into the optical fiber coupler to interfere. Under Heisebarg mapping, the output is
Figure BDA0001610299990000032
The wave function of the interference field is expressed as the direct product of the wave functions of the input field, i.e. | ψ1>＝|αsigαref>And probability of single photon detector output signal
Figure BDA0001610299990000033
Figure BDA0001610299990000034
η represents the transmission efficiency of the system, including the detection efficiency of the single photon detector, etc. the probability of the output signal of the final single photon detector is
Figure BDA0001610299990000035
Wherein, | αsig|2Is the average photon number of the signal light pulse, | αref|2Is the average photon number of the reference light pulse, phisigIs the phase of the signal light phirefIs the reference light phase. If the repetition frequency of the signal light pulse is equal to the repetition frequency of the reference light pulse and is f, the photon counting module measures the single photon counting by the integration time T, and the single photon counting is within the integration time
Figure BDA0001610299990000036
The photon counting module inputs the counting value N into the phase calculation module.
In order to obtain an accurate phase value, it is necessary to know the slope at which the photon count corresponds to the relative phase
Figure BDA0001610299990000037
The slope is obtained by perturbation, the phase calculation module applies perturbation voltage delta V to the phase modulation module, and if the phase variation of the signal light and the variation of the voltage applied by the phase modulation module have a linear relationship, the relative phase variation is
Figure BDA0001610299990000038
Wherein VπIs the half-wave voltage of the phase modulation module. The photon counting module collects a photon counting value N ' after the perturbation voltage delta V is applied by the integration time T and inputs the photon counting value N ' into the phase calculation module, and at the moment, the phase calculation module can determine the relative phase delta phi of the signal light field and the reference light field according to parameters such as the single photon counting value N, N '. When in use
Figure BDA0001610299990000039
Time, relative phase
Figure BDA00016102999900000310
Figure BDA0001610299990000041
When in use
Figure BDA0001610299990000042
Time, relative phase
Figure BDA0001610299990000043
The structure for converting the phase of the single photon optical field into the intensity by single photon interference is not limited to the 50:50 coupler structure, but also includes a sideband interference-based structure and the like.
The phase modulation module can be a Mach-Zehnder modulator, an electro-optic modulator, an acousto-optic modulator, a scanning mirror with piezoelectric ceramics and other devices for realizing optical field phase modulation.
The photon counting module can be realized based on hardware programming such as a Microcontroller (MCU), a Field Programmable Gate Array (FPGA) and the like.
The phase calculation module can be realized based on hardware programming such as a Microcontroller (MCU), a Field Programmable Gate Array (FPGA) and the like, and can also be realized based on software programming such as Matlab and the like used by a computer.
The parameters in the formula are η, f, | αsig|2And | αref|2Etc. are considered to be known values.
Preferably, when choosing the integration time T in a practical system, the phase resolution and the feedback rate should be considered. Assuming that the dark noise of the detection system is small, the phase resolution of the whole detection process is limited by the photon shot noise, and then the phase resolution
Figure BDA0001610299990000044
Too little integration time results in too poor phase resolution and too low locking accuracy. However feedback rate of the system
Figure BDA0001610299990000045
The larger integration time will result in a lower feedback rate and will not compensate for the faster phase drift in time, so the system needs to select the optimal integration time T.
Preferably, in a practical system, the perturbation voltage δ V should be as close as possible to the ideal value
Figure BDA0001610299990000046
S3, comparing the measured relative phase delta phi with the set reference phase delta phirComparing the two values, and determining the absolute value of the difference between the two valuesrI and the set threshold phase phithAnd (3) selecting and utilizing a phase estimation algorithm or a search algorithm to calculate an optimized phase adjustment voltage and adjusting the phase of the signal light field.
The phase estimation algorithm means that the phase adjusted by the phase modulation module in the signal light path is assumed to be linear response to the input voltage, and the voltage value required to be loaded on the phase modulation module is calculated according to the difference value of the actual relative phase and the set reference phase. This step can greatly reduce the time required for lock when the actual relative phase is far from the reference phase.
The search algorithm is that when the actual relative phase is closer to the reference phase, the difference sign between the relative phase and the reference phase before and after the perturbation is applied is observed by applying the perturbation, so as to judge the phase adjustment direction, and the phase is continuously adjusted in the same direction without adjusting the phase or reversely adjusting the phase. More accurate phase locking around the set value can be achieved using a search algorithm.
The method comprises the following specific steps:
in the phase calculation module, the relative phase delta phi is compared with a reference phase delta phirIf the absolute value of the difference is | Δ φ - Δ φrI is greater than the threshold phase phithAnd estimating the optimized applied voltage value of the phase modulation module according to a phase estimation algorithm. The phase estimation algorithm is based on the formula
Figure BDA0001610299990000051
Figure BDA0001610299990000052
Calculating the change value of the applied voltage on the phase modulation module, and the newly optimized phase modulation module applied voltage value VAnd V + delta V, wherein V is the applied voltage value of the phase modulation module before optimization. If the absolute value of the difference is | Δ φ - Δ φrPhase phi of | less than thresholdthThen a search algorithm is used to obtain a new optimized phase modulation module applied voltage value. The search algorithm is based on the formula
Figure BDA0001610299990000053
Calculating the applied voltage value of the newly optimized phase modulation module, wherein delta phi 'is the relative phase corresponding to the two light fields after the perturbation voltage delta V is applied, and when (delta phi' -delta phi)r)|-|(Δφ-Δφr) When | ═ 0, no voltage is applied to the phase modulation module. The combination of the two algorithms can realize that when the phase offset is too large, the system quickly converges to the vicinity of the required phase, and when the phase offset is smaller, the system carries out phase feedback with higher precision.
And the phase calculation module applies an optimized voltage signal to the phase modulation module so as to adjust the phase of the single photon optical field.
Preferably, the threshold phase phithHas a value range of (phi)resPi), but not too large, otherwise the phase shift is too large, which may result in the situation where the phase drift cannot be compensated for quickly by the phase estimation algorithm.
And S4, repeating the steps S2 and S3 to realize the real-time locking of the single photon phase.
The method for locking the single photon phase has the following advantages:
1. the phase locking precision of the method is higher than that of the traditional phase locking method.
2. The method can be applied to a phase coding quantum key distribution system for compensating phase drift, does not need phase scanning and information exchange, reduces phase compensation time and system complexity, and improves locking efficiency and system safety.
3. The method is a universal method and is suitable for other laser communication systems needing to compensate single photon phase drift.
The invention provides a method for locking single photon phases in real time, which converts the relative phases of two single photon light fields into physically measurable intensity by using a single photon interference method, and measures the statistic value of the single photon intensity by using a single photon counting method, thereby realizing the measurement of the relative phases of the two single photon light fields. And comparing the measured relative phase with a set reference phase, calculating the optimized phase adjusting voltage by using a phase estimation algorithm when the deviation between the measured relative phase and the set reference phase is large so as to quickly perform phase feedback, calculating the optimized phase adjusting voltage by using a search algorithm when the deviation between the measured relative phase and the set reference phase is small, and locking the relative phases of the two single photon light fields by continuously repeating the steps. The method can be applied to locking the phase of the single photon signal in the phase coding quantum key distribution system, and has the advantages of simple operation, high locking efficiency and high precision.
Drawings
FIG. 1 shows a schematic block diagram of locking single photon phases in a single probe equal arm Mach-Zehnder interferometer system, where the dashed lines represent optical signals and the solid lines represent electrical signals.
Figure 2 shows a flow chart of the system locking single photon phase.
Detailed Description
The following detailed description of specific embodiments of the invention refers to the accompanying drawings.
A method for locking the phase of a single photon in real time reflects the degree of phase drift of the single photon through the interference intensity of single photon pulses, loads an optimized control signal to a phase modulation module by using a feedback circuit, and keeps a single photon interference counting value at a fixed value, so that the relative phase of the single photon can be effectively locked.
The method can be applied to a phase coding quantum key distribution system, such as a Mach-Zehnder interferometer system or a sideband interference system, by combining a time division multiplexing technology, so that the interference visibility of single photons is improved, and the system can realize long-time stable key output. The following describes the implementation process of the method in detail by taking a single-probe equal-arm Mach-Zehnder interferometer as an experimental system.
A schematic block diagram based on locking single photon phase in a single-probe equal-arm Mach-Zehnder interferometer system is shown in figure 1, and the system comprises a laser, wherein the output end of the laser is connected with the input end of a beam splitter (50:50), one output end of the beam splitter is connected with the input end of a first electro-optical modulator, the output end of a first Field Programmable Gate Array (FPGA) is connected with the control end of the first electro-optical modulator, and the output end of the first electro-optical modulator is connected with one input end of a beam combiner (50: 50). The second output end of the beam splitter is connected with the input end of the second electro-optical modulator, the second FPGA output end is connected with the control end of the second electro-optical modulator, and the second electro-optical modulator output end is connected with the second input end of the beam combiner. The output end of the beam combiner is connected with the input end of the single photon detector, the output end of the single photon detector is connected with the input end of a third FPGA, and the output end of the third FPGA is connected with the input end of a second FPGA.
At the transmitting side, the laser is used for generating single photon pulse light (the average photon number is about 0.1), and the single photon pulse light is divided into time division multiplexing phase compensation pulses and signal pulses, the interference intensity of the phase compensation pulses is used for locking the single photon phase, and the signal pulses are used as information carriers for generating quantum keys. The first FPGA is used for generating a voltage signal to control the first electro-optical modulator, and the first electro-optical modulator is used for carrying out phase modulation on an input single photon pulse and carrying out phase modulation of a fixed phase on a phase compensation pulse.
At the receiver, a second electro-optic modulator is used to phase demodulate the incoming single photon pulses. After the phase compensation pulse is demodulated, the single photon detector detects the interference intensity of the single photon, outputs corresponding digital pulses, counts and counts the digital pulses by a third FPGA, inputs the count value to a second FPGA, the second FPGA is used for analyzing and calculating the count value, and outputs an optimized demodulation voltage signal to be loaded on a second electro-optic modulator, so that the phase compensation pulse is demodulated, the interference intensity of the phase compensation pulse is maintained at a fixed value, and the phase of the phase compensation pulse can be locked.
The phase compensation pulse output by the laser is divided into two beams after passing through the beam splitter, the first beam of single photon signal is phase-modulated by the first electro-optical modulator, and the modulation phase is phiaThe annihilation operator of the single-photon signal is represented as
Figure BDA0001610299990000081
The wave function is represented as | αa>. The second beam single photon signal is phase-modulated by a second electro-optical modulator with a modulation phase phibThe annihilation operator of the single-photon signal is represented as
Figure BDA0001610299990000082
The wave function is represented as | αb>. The average photon number of the single photon pulse of the two arms of the interferometer is the same, two beams of single photon signals enter the beam combiner and are coupled together to generate interference, and the output is
Figure BDA0001610299990000091
The wave function of the interference field is expressed as the direct product of the wave functions of the input field, i.e. | ψ1〉＝|αaαb>And the probability of the output signal of the single photon detector is
Figure BDA0001610299990000092
η represents the transmission efficiency of the system, including the detection efficiency of the single photon detector, etc. the probability of the output signal of the final single photon detector is
Pout＝η|α|2[1+cos(φa-φb)](1)
Wherein | α | ceiling2＝|αa|2＝|αb|2Is the average number of photons on one arm of the interferometer. If the repetition frequency of the optical pulse is f and the integral time of the single photon counting is T, the photon counting measured by the single photon detector is T within the integral time
N＝fηT|α|2[1+cos(φa-φb)](2)
The relative phase of the two paths of single photon signals is
Figure BDA0001610299990000093
The obtained relative phase is in [0, π]An interval. To obtain the true phase, it is also necessary to know the slope at which the photon count corresponds to the relative phase
Figure BDA0001610299990000094
The slope is obtained by perturbation, i.e. applying perturbation voltage delta V on the second electro-optical modulator, and assuming that the phase variation of the signal light has linear relation with the variation of the voltage applied by the second electro-optical modulator, the relative phase variation is
Figure BDA0001610299990000095
Wherein VπIs the half-wave voltage of the second electro-optic modulator. Collecting photon count value N' after applying perturbation voltage delta V, if the perturbation voltage delta V is smaller, then
Figure BDA0001610299990000096
When k is less than 0, there are
Figure BDA0001610299990000097
When k > 0, there are
Figure BDA0001610299990000098
Note that the reference phase to be locked is delta phir，Δφr∈ [0, 2 pi.) the flow of a single photon phase in a quantum key distribution system of an equal-arm Mach-Zehnder interferometer by using a single photon interference method and single photon counting statistical locking is shown in FIG. 2, which specifically comprises the following steps:
1. initializing system settings;
2. the first FPGA loads a fixed voltage signal to the first electro-optical modulator to perform phase modulation on the phase compensation pulse;
3. the second FPGA applies a set voltage signal to the second electro-optical modulator to perform phase modulation on the phase compensation pulse;
4. measuring the interference intensity of the phase compensation pulse by the single photon detector, and counting the corresponding phase compensation pulse interference count value N in the integration time T by the third FPGAtAnd inputting the data into a second FPGA;
5. the second FPGA applies perturbation voltage delta V to the second electro-optical modulator, and the third FPGA counts corresponding phase compensation pulse interference count values N 'in the integration time T'tAnd inputting the data into a second FPGA;
6. the second FPGA determines the relative phase delta phi of the two communication parties;
7. in the second FPGA, the relative phase delta phi is compared with the reference phase delta phirIf the absolute value of the difference is | Δ φ - Δ φrI is greater than the threshold phase phithThe optimized voltage signal loaded to the second electro-optic modulator is estimated according to a phase estimation algorithm according to a formula
Figure BDA0001610299990000101
An applied voltage change value is calculated, and the applied voltage value V' of the newly optimized second electro-optical modulator is V + Δ V, where V is the applied voltage value before optimization. If the absolute value of the difference is | Δ φ - Δ φrPhase phi of | less than thresholdthObtaining a new optimized phase modulation signal using a search algorithm according to the formula
Figure BDA0001610299990000102
Calculating the newly optimized applied voltage value of the second electro-optical modulator, wherein delta phi 'is the corresponding relative phase of the second FPGA and the second FPGA after the perturbation voltage delta V is applied, and delta phi' -delta phir)|-|(Δφ-Δφr) When | ═ 0, no voltage is applied to the second electro-optical modulator. The combination of the two algorithms can realize that the phase position can be quickly converged to the vicinity of the required phase position when the phase position distance is far, and the phase position feedback can be carried out with higher precision when the phase position distance is close;
8. the second FPGA applies an optimized voltage signal to the second electro-optical modulator for phase modulation;
9. and (4) repeatedly executing the steps 4-8 by the system, so that the real-time locking of the single photon phase can be realized.
Finally, it should be noted that the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting, and although the detailed description is made with reference to the embodiments of the present invention, it should be understood by those skilled in the art that modifications or equivalent substitutions may be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, which shall be covered by the claims of the present invention.

Claims (4)

1. A method for locking single photon phase in real time is characterized in that: the method comprises the following steps:
s1, marking the two single photon light fields as a reference light field and a signal light field respectively, wherein the phase of the signal light field can be adjusted, and setting the reference phase delta phi to be lockedr，Δφr∈[0，2π)；
S2, measuring the relative phase delta phi between the two single photon optical fields; the method comprises the following specific steps:
the signal light field is input to the input end of the phase modulation module, the output end of the phase modulation module is connected to one input end of the optical fiber coupler, the reference light field is input to two input ends of the optical fiber coupler, the two single photon light fields meet in the optical fiber coupler to generate interference, the output end of the optical fiber coupler is connected to the input end of the single photon detector, the output end of the single photon detector is connected to the input end of the photon counting module, the output end of the photon counting module is connected to the input end of the phase calculation module, the output end of the phase calculation module is connected to the voltage input end of the;
the signal light field is coherent light field, and its annihilation operator is expressed as
Figure FDA0002436132240000011
The wave function is represented as | αsig>(ii) a The reference light field is coherent light field, and its annihilation operator is expressed as
Figure FDA0002436132240000012
The wave function is represented as | αref>(ii) a The signal light and the reference light have the same frequency and polarization direction, and the two beams of light are input into the optical fiber coupler to generate interference; under Heisebarg mapping, the output is
Figure FDA0002436132240000013
The wave function of the interference field is expressed as the direct product of the wave functions of the input field, i.e. | ψ1>＝|αsigαref>And probability of single photon detector output signal
Figure FDA0002436132240000014
Figure FDA0002436132240000015
η represents the transmission efficiency of the system, and the probability of the output signal of the final single-photon detector is
Figure FDA0002436132240000016
Wherein, | αsig|2Is the average photon number of the signal light pulse, | αref|2Is the average photon number of the reference light pulse, phisigIs the phase of the signal light phirefIs the reference light phase; if the repetition frequency of the signal light pulse is equal to the repetition frequency of the reference light pulse and is f, the photon counting module measures the single photon counting by the integration time T, and the single photon counting is within the integration time
Figure FDA0002436132240000021
The photon counting module inputs a counting value N into the phase calculation module;
to obtain the true phase, it is also necessary to know the slope at which the photon count corresponds to the relative phase
Figure FDA0002436132240000022
The slope is obtained by perturbation, the phase calculation module applies perturbation voltage delta V to the phase modulation module, and if the phase variation of the signal light and the variation of the voltage applied by the phase modulation module have a linear relationship, the relative phase variation is
Figure FDA0002436132240000023
Wherein VπIs the half-wave voltage of the phase modulation module; the photon counting module collects and applies perturbation voltage by integration time TThe single photon counting value N 'after delta V is input into the phase calculation module, and at the moment, the phase calculation module can determine the relative phase delta phi of the signal light field and the reference light field according to the parameters such as the single photon counting value N, N' and the like; when in use
Figure FDA0002436132240000024
Time, relative phase
Figure FDA0002436132240000025
Figure FDA0002436132240000026
When in use
Figure FDA0002436132240000027
Time, relative phase
Figure FDA0002436132240000028
S3, comparing the measured relative phase delta phi with the set reference phase delta phirComparing the two values, and determining the absolute value of the difference between the two valuesrI and the set threshold phase phithThe optimized phase adjusting voltage is calculated by selecting a phase estimation algorithm or a search algorithm, and the phase of the signal light field is adjusted; the method comprises the following specific steps:
if the relative phase delta phi and the reference phase delta phirAbsolute value of difference | Δ φ - Δ φrI is greater than the threshold phase phithEstimating the optimized applied voltage value of the phase modulation module according to a phase estimation algorithm according to a formula
Figure FDA0002436132240000029
Calculating a change value of the applied voltage on the phase modulation module, wherein the newly optimized phase modulation module applied voltage value V is V + delta V, and V is the applied voltage value of the phase modulation module before optimization;
if the relative phase delta phi and the reference phase delta phirAbsolute value of difference | Δ φ - Δ φr| less than thresholdValue phase phithObtaining a new optimized phase modulation module applied voltage value using a search algorithm according to a formula
Figure FDA0002436132240000031
Calculating a new optimized phase modulation module applied voltage value, where′Is the relative phase corresponding to the two light fields after applying perturbation voltage delta V, when (delta phi' -delta phi)r)|-|(Δφ-Δφr) When | ═ 0, no voltage is applied to the phase modulation module;
the phase calculation module applies an optimized voltage signal to the phase modulation module so as to adjust the phase of the single photon optical field;
and S4, repeating the steps S2 and S3 to realize the real-time locking of the single photon phase.
2. The method for locking single photon phases in real time according to claim 1, characterized in that: the perturbation voltage
Figure FDA0002436132240000032
Phase resolution
Figure FDA0002436132240000033
3. The method for locking single photon phases in real time according to claim 1, characterized in that: the phase modulation module is a Mach-Zehnder modulator, an electro-optic modulator, an acousto-optic modulator or a scanning mirror with piezoelectric ceramics;
the photon counting module is realized by hardware programming based on a microcontroller and a field programmable gate array;
the phase calculation module is realized by hardware programming based on a microcontroller and a field programmable gate array, or by Matlab software programming based on a computer.
4. The method of locking single photon phases in real time according to claim 1, characterized in thatThe method comprises the following steps: the threshold phase phithHas a value range of (phi)res，π)。
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