A continuous variable quantum key distribution method based on hardware synchronization

Abstract

The present application belongs to the field of continuous variable quantum key distribution, and particularly relates to a continuous variable quantum key distribution method based on hardware synchronization. The present application controls the timing signals of different instruments through a controller, specifically: at the sending end, a first controller is used to control an arbitrary waveform generator to output a synchronization signal, and to control the timing of the output pulses of a digital pulse generator, and the generated local oscillation light field and signal light field are transmitted to the receiving end through a quantum channel; at the receiving end, a second controller is used to control a pulse generator and a second and third multifunctional input / output card, and the generated clock signal can correspond one-to-one with the peak value of the electrical pulses output by a detection device, and the clock signal is synchronized and aligned with the electrical pulses, until the collection of the entire data block is completed. Compared with the frame synchronization and peak compensation method, the present application is easy to implement, does not require complex software layer algorithms, and can greatly shorten the development cycle of the continuous variable quantum key distribution system.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of continuous variable quantum key distribution, and particularly relates to a continuous variable quantum key distribution method based on hardware synchronization. BACKGROUND

[0002] With the development of quantum information technology, quantum key distribution (QKD) technology characterized by high security has become a research hotspot in the field of quantum communication. Quantum key distribution technology is based on the Heisenberg uncertainty principle and the principle of quantum state non-cloning in quantum mechanics, and has unconditional security in theory. At present, in the face of the increasing amount of data required by the encryption system, the low-speed continuous variable quantum key distribution cannot meet the actual needs in the future. How to realize high-speed quantum key distribution has become a problem to be solved.

[0003] In a continuous variable quantum key distribution (CV-QKD) system, how to design and realize the timing and synchronization of each component in the system by the sending end and the receiving end of the communication party is the basis for realizing high-speed sending and receiving of data. The document "Continuous variable quantum key distribution system synchronization scheme and implementation [J]. Journal of Quantum Optics, 2016(1):43-49." reports a synchronization scheme based on m sequence. The influencing factors of m sequence in the scheme are simulated by using matlab, and the results show that this method has good noise resistance and error code tolerance. The document "High-speed continuous variable quantum key distribution system synchronization technology research [J]. Acta Optica Sinica, 2015, 35(1)." reports a simple and efficient bit frame synchronization theory scheme. The feasibility of the scheme is verified on a high-speed continuous variable quantum key distribution system with a repetition frequency of 25MHz. Through experimental data, all parameters in the bit frame synchronization scheme are analyzed experimentally, the influence of the parameters on the success rate is obtained, and the theoretical time required for synchronization is given. Most of the existing synchronization schemes of CV-QKD system are based on software layer algorithm, and the synchronization frame or sequence structure is constructed. The peak value of the collected data is monitored and compensated, which improves the complexity of the system and increases the running time of the system. In such a scheme, the sender generates a special data synchronization frame structure, and then sends it to the receiver through the quantum channel. The receiver uses the detected regular component to search for the synchronization frame by selecting appropriate parameters, and then identifies the starting position of the valid data to realize the synchronization of the communication party. However, in actual system operation, the software layer algorithm is relatively complex, and the synchronization frame data is easily affected by external environment (such as mechanical vibration, temperature and humidity, etc.). This will cause the error code phenomenon in the transmission of the underlying physical layer. In addition, the selection of the synchronization frame parameter is also a complex process. SUMMARY

[0004] In order to solve the technical problems existing in the above-mentioned prior art, the present invention provides a hardware synchronization method in a continuous variable quantum key distribution system that is simple to operate and does not require complex software layer algorithms. This method is applied to the actual experimental system of continuous variable quantum key distribution and can achieve synchronization of data sending and receiving.

[0005] To achieve the above object, the present invention is implemented through the following technical solutions:

[0006] A continuous variable quantum key distribution method based on hardware synchronization comprises the following steps:

[0007] In the transmitting end: the first controller controls the arbitrary waveform generator to synchronously output arbitrary waveforms of three channels; channel one outputs a clock signal to the digital pulse generator, which is used to trigger the digital pulse generator to generate multi-channel pulse signals. The pulse signal generates a signal light field and a local oscillator light field after passing through the pulse light generating device; channel two outputs an amplitude modulated signal to the first amplitude modulator, and channel three outputs a phase modulated signal to the first phase modulator; the signal light field passes through the first amplitude modulator, the first phase modulator, and the first signal adjustment device, and is transmitted to the fiber polarization combiner. After being combined with the local oscillator light field into a quantum signal, it is transmitted to the receiving end through the quantum channel;

[0008] The first controller controls the pulse width, delay and triggering mode of the multi-channel pulses output by the digital pulse generator;

[0009] The first controller controls the first multifunctional input / output card to lock the bias voltages of the pulse light generating device, the amplitude modulators in the first signal adjusting device, and the first amplitude modulator, and to read the feedback signal of the first signal adjusting device to lock the signal light field intensity to a required intensity;

[0010] In the receiving end: the second controller controls the second multifunctional input / output card to generate multi-channel analog voltage and digital voltage signals, and at the same time receives the feedback signal from the second signal adjustment device; the analog voltage signal and the feedback signal are used to control the dynamic polarization control device to complete the locking of the polarization state of the signal light field and the local oscillator light field passing through the quantum channel; the locked signal light field and the local oscillator light field are re-divided into the signal light field and the local oscillator light field by the optical fiber polarization beam splitter; after the local oscillator light field passes through the second signal adjustment device, the electrical pulse signal required for clock recovery is generated, which is used to trigger the pulse generator to generate a two-channel delayed synchronous clock signal. The clock signal The pulse width and delay of the signal are controlled by the second controller; wherein, the pulse signal output by channel one is input to the second multifunctional input / output card, which generates the modulation signal required for the random switching measurement base, modulates the phase of the local oscillator light field passing through the second phase modulator, and the pulse signal output by channel two is input to the third multifunctional input / output card, and is synchronized and aligned with the electrical pulse signal output by the detection device to ensure accurate measurement and acquisition of the peak value of the output electrical pulse signal; the detection device completes the measurement of the orthogonal component of the signal light field by receiving the signal light field and the local oscillator light field, and outputs the corresponding electrical pulse signal, whose peak value is linearly related to the orthogonal component;

[0011] The second controller controls the third multifunctional input / output card. The input pulse signal corresponds to the peak value of the electrical pulse signal output by the detection device, and is synchronized and aligned. When the first clock signal is received, the first electrical pulse peak signal is collected, and the collection is completed until the entire data block is collected. This process is hardware synchronization and does not require subsequent software algorithm synchronization. Afterwards, the second controller reads the data from the third multifunctional input / output card.

[0012] The first controller at the transmitting end and the second controller at the receiving end are connected through a classical channel to complete data screening, parameter estimation, data coordination, privacy amplification, and security key generation in the quantum key distribution process.

[0013] Furthermore, the pulse light generating device includes a fiber laser, a second amplitude modulator, a third amplitude modulator, and a first polarization-maintaining fiber coupler;

[0014] The second amplitude modulator and the third amplitude modulator are cascaded between the fiber laser and the first polarization-maintaining fiber coupler, and are respectively connected to a digital pulse generator, so as to generate pulsed light with a high extinction ratio under the drive of the electrical pulse signal output by the digital pulse generator; the first polarization-maintaining fiber coupler splits the pulsed light into a signal light field and a local oscillator light field.

[0015] Furthermore, the first signal adjustment device includes a fourth amplitude modulator, a second polarization-maintaining fiber coupler, a first photodetector, a first polarization-maintaining fiber, and an adjustable optical attenuator;

[0016] The fourth amplitude modulator is used to control the intensity of the test pulse; the second polarization-maintaining fiber coupler and the first photodetector are used to output an electrical pulse signal and feed it back to the first multi-functional input / output card; the first polarization-maintaining fiber delays the pulse light of the signal light field at the transmitting end for time division multiplexing; and the adjustable optical attenuator is used to attenuate the signal light field intensity to an appropriate intensity.

[0017] Furthermore, the second signal adjustment device includes a third polarization-maintaining fiber coupler, a second photodetector, and a second polarization-maintaining fiber;

[0018] After the third polarization-maintaining fiber coupler separates part of the local oscillation light field, it generates an electrical pulse signal for recovering the clock through the second photodetector, and the remaining part of the light field is delayed through the second polarization-maintaining fiber. The second polarization-maintaining fiber corresponds to the first polarization-maintaining fiber to ensure that the signal light field and the local oscillation light field reach the detection device at the same time.

[0019] Furthermore, the detection device includes a first polarizer, a second polarizer, a 50 / 50 fiber-coupled beam splitter, and a first balanced homodyne detector;

[0020] The first polarizer, the 50 / 50 fiber-coupled beam splitter and the first balanced homodyne detector are connected in sequence, and the second polarizer, the 50 / 50 fiber-coupled beam splitter and the first balanced homodyne detector are connected in sequence;

[0021] The first polarizer and the second polarizer are used to improve the polarization extinction ratio of the signal light field and the local oscillator light field respectively; the first balanced homodyne detector adopts a time domain detector to detect the orthogonal components of the signal light field.

[0022] Furthermore, the detection device includes a first polarizer, a second polarizer, a 90° optical mixer, a second balanced homodyne detector, and a third balanced homodyne detector;

[0023] The input end of the 90° optical mixer is connected to the first polarizer and the second polarizer respectively, and the output end is connected to the second balanced homodyne detector and the third balanced homodyne detector respectively;

[0024] The first polarizer and the second polarizer are used to improve the polarization extinction ratio of the signal light field and the local oscillator light field respectively; the second balanced homodyne detector and the third balanced homodyne detector use time domain detectors to detect the orthogonal components of the signal light field.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The present invention is simple to operate and does not require complex software-layer algorithms. It only requires cleverly controlling the timing signals of different instruments through a controller, inputting the signals required by the transmitter and receiver in the CV-QKD system into the system, and appropriately delaying the clock of the receiver to correspond one-to-one with the peak value of the electric pulse signal output by the time-domain balanced homodyne (heterodyne) detector, synchronizing and aligning them. When the first clock signal is received, the first electric pulse peak signal can be collected until the collection of the entire data block is completed. This method does not require complex software algorithm operations for synchronization, and all instruments can be controlled by the controller, making operation convenient and fast. The present invention can shorten the development cycle of high-speed CV-QKD systems, improve the controllability and operability of the system, and can be extended to different high-speed CV-QKD systems while meeting the instrument performance requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A schematic diagram of a system for implementing a continuous variable quantum key distribution method based on hardware synchronization according to the present invention;

[0028] Figure 2 for Figure 1 Schematic diagram of the medium pulse light generating device;

[0029] Figure 3 for Figure 1 A schematic diagram of a first signal adjustment device;

[0030] Figure 4 for Figure 1 A schematic diagram of a second signal adjustment device;

[0031] Figure 5 for Figure 1 Schematic diagram of the detection device;

[0032] Figure 6 Schematic diagram of the GMCS CV-QKD system in an embodiment of the present invention;

[0033] Figure 7 Schematic diagram of multi-channel synchronous output waveforms of a signal generator according to an embodiment of the present invention;

[0034] Figure 8 Schematic diagram of a pulse waveform output by a digital pulse generator according to an embodiment of the present invention;

[0035] Figure 9 Schematic diagram of the phase space of a test pulse and a physical quantity measured using the test pulse in an embodiment of the present invention;

[0036] Figure 10 1 is a graph showing the excess noise and key rate of different data blocks received at a fixed loss of 10 dB in the system according to an embodiment of the present invention.

[0037] In the figure: 1-first controller, 2-arbitrary waveform generator, 3-digital pulse generator, 4-pulse light generating device, 5-first amplitude modulator, 6-first phase modulator, 7-first signal adjustment device, 8-fiber polarization combiner, 9-first multi-function input / output card, 10-quantum channel, 11-dynamic polarization control device, 12-fiber polarization beam splitter, 13-second signal adjustment device, 14-second phase modulator, 15-pulse generator, 16-detection device, 17-second multi-function input / output card, 18 second controller, 19-third multi-function input / output card, 20-classical channel;

[0038] 401 - fiber laser, 402 - second amplitude modulator, 403 - third amplitude modulator, 404 - first polarization-maintaining fiber coupler;

[0039] 701 - fourth amplitude modulator, 702 - second polarization-maintaining fiber coupler, 703 - first photodetector, 704 - first polarization-maintaining fiber, 705 - adjustable optical attenuator;

[0040] 1301 - third polarization-maintaining fiber coupler, 1302 - second photodetector, 1303 - second polarization-maintaining fiber;

[0041] 1601 - first polarizer, 1602 - second polarizer, 1603 - 50 / 50 fiber-coupled beam splitter, 1604 - first balanced homodyne detector, 1605 - 90° optical mixer, 1606 - second balanced homodyne detector, 1607 - third balanced homodyne detector. DETAILED DESCRIPTION

[0042] To facilitate understanding of the present invention, the present invention will be described more fully below.

[0043] The purpose of this invention is to provide a continuous variable quantum key distribution method based on hardware synchronization, such as Figure 1 As shown, the following steps are included:

[0044] In the transmitting end: the first controller 1 controls the arbitrary waveform generator 2 to synchronously output arbitrary waveforms of three channels; channel one outputs a clock signal to the digital pulse generator 3, which is used to trigger the digital pulse generator 3 to generate multi-channel pulse signals. The pulse signals generate signal light fields and local oscillation light fields after passing through the pulse light generating device 4; channel two outputs an amplitude modulated signal to the first amplitude modulator 5; channel three outputs a phase modulated signal to the first phase modulator 6; the signal light field passes through the first amplitude modulator 5, the first phase modulator 6, and the first signal adjustment device 7, and is transmitted to the fiber polarization combiner 8. After being combined with the local oscillation light field into a quantum signal, it is transmitted to the receiving end through the quantum channel 10;

[0045] The first controller 1 controls the pulse width, delay and triggering mode of the multi-channel pulses output by the digital pulse generator 3;

[0046] The first controller 1 controls the first multifunctional input / output card 9 to lock the bias voltages of the pulse light generating device 4, the amplitude modulators in the first signal adjusting device 7, and the first amplitude modulator 5, and to read the feedback signal of the first signal adjusting device 7 to lock the signal light field intensity to a required intensity;

[0047] In the receiving end: the second controller 18 controls the second multifunctional input / output card 17 to generate multi-channel analog voltage and digital voltage signals, and at the same time receives the feedback signal from the second signal adjustment device 13; the analog voltage signal and the feedback signal are used to control the dynamic polarization control transposition 11 to complete the locking of the polarization state of the signal light field and the local oscillator light field passing through the quantum channel 10; the locked signal light field and the local oscillator light field are re-divided into the signal light field and the local oscillator light field by the optical fiber polarization beam splitter 12; after the local oscillator light field passes through the second signal adjustment device 13, it generates the electrical pulse signal required for clock recovery, which is used to trigger the pulse generator 15 to generate a two-channel delayed synchronous clock signal. The pulse width and delay of the clock signal are controlled by the second controller 18; the clock signal output by channel one is input to the second multifunctional input / output card 17, which generates the modulation signal required for the random switching measurement base, modulates the phase of the local oscillator light field passing through the second phase modulator 14, and the clock signal output by channel two is input to the third multifunctional input / output card 19, which is synchronized and aligned with the electrical pulse signal output by the detection device 16 to ensure accurate measurement and acquisition of the peak value of the output electrical pulse signal; the detection device 16 completes the measurement of the orthogonal component of the signal light field by receiving the signal light field and the local oscillator light field, and outputs the corresponding electrical pulse signal, whose peak value is linearly related to the orthogonal component;

[0048] The second controller 18 controls the third multifunctional input / output card 19. The input pulse signal corresponds to the peak value of the electrical pulse signal output by the detection device 16, and is synchronized and aligned. When the first clock signal is received, the first electrical pulse peak signal can be collected, and the collection of the entire data block is completed. This process is hardware synchronization and does not require subsequent software algorithm synchronization. Afterwards, the second controller 18 reads data from the third multifunctional input / output card 19.

[0049] The first controller 1 at the transmitting end and the second controller 18 at the receiving end are connected via a classical channel 20 to complete data screening, parameter estimation, data coordination, privacy amplification, and key generation in the process of quantum key distribution.

[0050] Specifically, if Figure 2As shown, the pulse light generating device 4 includes a fiber laser 401, a second amplitude modulator 402, a third amplitude modulator 403, and a first polarization-maintaining fiber coupler 404;

[0051] The second amplitude modulator 402 and the third amplitude modulator 403 are cascaded between the fiber laser 401 and the first polarization-maintaining fiber coupler 404, and are respectively connected to the digital pulse generator 3, and are used to generate pulsed light with a high extinction ratio under the drive of the electrical pulse signal output by the digital pulse generator 3; the first polarization-maintaining fiber coupler 404 splits the pulsed light into a signal light field and a local oscillator light field.

[0052] Specifically, if Figure 3 As shown, the first signal adjustment device 7 includes a fourth amplitude modulator 701, a second polarization-maintaining fiber coupler 702, a first photodetector 703, a first polarization-maintaining fiber 704, and an adjustable optical attenuator 705;

[0053] The fourth amplitude modulator 701 is used to control the intensity of the test pulse; the second polarization-maintaining fiber coupler 702 and the first photodetector 703 are used to output electrical pulse signals and feed them back to the first multi-functional input / output card 9; the first polarization-maintaining fiber 704 delays the pulse light of the signal light field at the transmitting end for time division multiplexing; and the adjustable optical attenuator 705 is used to attenuate the signal light field intensity to an appropriate intensity.

[0054] Specifically, if Figure 4 As shown, the second signal adjustment device 13 includes a third polarization-maintaining fiber coupler 1301, a second photodetector 1302, and a second polarization-maintaining fiber 1303;

[0055] After the third polarization-maintaining fiber coupler 1301 separates part of the local oscillation light field, it generates an electrical pulse signal for recovering the clock through the second photodetector 1302, and the remaining part of the light field is delayed through the second polarization-maintaining fiber 1303. The second polarization-maintaining fiber 1303 corresponds to the first polarization-maintaining fiber 704 to ensure that the signal light field and the local oscillation light field reach the detection device 16 at the same time.

[0056] Specifically, if Figure 5 As shown in (1), if a zero-beat detection scheme is adopted, the detection device 16 includes a first polarizer 1601, a second polarizer 1602, a 50 / 50 fiber-coupled beam splitter 1603, and a first balanced homodyne detector 1604;

[0057] The first polarizer 1601, the 50 / 50 fiber-coupled beam splitter 1603 and the first balanced homodyne detector 1604 are connected in sequence, and the second polarizer 1602, the 50 / 50 fiber-coupled beam splitter 1603 and the first balanced homodyne detector 1604 are connected in sequence;

[0058] The first polarizer 1601 and the second polarizer 1602 are used to improve the polarization extinction ratio of the signal light field and the local oscillator light field respectively; the first balanced homodyne detector 1604 adopts a time domain detector to detect the orthogonal components of the signal light field.

[0059] Specifically, if Figure 5 As shown in (2), if a heterodyne detection scheme is adopted, the detection device 16 includes a first polarizer 1601, a second polarizer 1602, a 90° optical mixer 1605, a second balanced homodyne detector 1606, and a third balanced homodyne detector 1607;

[0060] The input end of the 90° optical mixer 1605 is connected to the first polarizer 1601 and the second polarizer 1602 respectively, and the output end is connected to the second balanced homodyne detector 1606 and the third balanced homodyne detector 1607 respectively;

[0061] The first polarizer 1601 and the second polarizer 1602 are used to improve the polarization extinction ratio of the signal light field and the local oscillator light field respectively; the second balanced homodyne detector 1606 and the third balanced homodyne detector 1607 use time domain detectors to detect the orthogonal components of the signal light field.

[0062] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to specific embodiments.

[0063] Example

[0064] like Figure 6 As shown in the figure, a Gaussian Modulated Coherent State Continuous variable quantum key distribution (GMCS CV-QKD) system with a repetition frequency of 10 MHz is used to implement a continuous variable quantum key distribution method based on hardware synchronization. In the GMCS CV-QKD system,

[0065] Transmitter: The first controller 1 uses an industrial personal computer, the arbitrary waveform generator 2 uses a TFG 2944A, the digital pulse generator 3 uses an ASG 8100, the first multi-function input / output card 9 uses a USB 6259, the amplitude modulator uses a Mach-Zehnder interferometer modulator based on a lithium niobate crystal, the first polarization-maintaining fiber coupler 404 uses a 99 / 1 polarization-maintaining fiber coupler, and the second polarization-maintaining fiber coupler 702 uses a 50 / 50 polarization-maintaining fiber coupler;

[0066] The first industrial computer controls TFG 2944A to output three channels of arbitrary waveforms synchronously. The real data waveform is shown in Figure 7; Channel one outputs a base clock signal with a frequency of 20MHz to ASG 8100, which can trigger ASG 8100 to generate two pulse signals with a frequency of 10MHz. The second amplitude modulator 402 and the third amplitude modulator 403 are cascaded between the fiber laser 401 and the 99 / 1 polarization-maintaining fiber coupler to generate pulsed light with a high extinction ratio. After passing through the 99 / 1 polarization-maintaining fiber coupler, the signal light field and the local oscillator light field are split; Channel two outputs an amplitude modulated signal with a frequency of 10MHz to the first amplitude modulator 5, and channel three outputs a phase modulated signal with a frequency of 10MHz to the first phase modulator 6; After the signal light field is Gaussian modulated by the first amplitude modulator 5 and the first phase modulator 6, it is transmitted to the fourth amplitude modulator 701 to control the intensity of the test pulse, and then divided into two paths through the 50 / 50 polarization-maintaining fiber coupler, one of which is connected to the first photodetector 703 to output an electrical pulse signal to the USB 6259, the other path passes through the first polarization-maintaining fiber 704 to delay the signal light field for time division multiplexing, is attenuated by the variable optical attenuator 705, and is transmitted to the fiber polarization combiner 8. After being combined with the local oscillator light field to form a quantum signal, it is transmitted to the receiving end through the quantum channel 10;

[0067] The first industrial computer controls the output of the two-channel pulse of ASG8100 with a pulse width of 20ns and a delay of 18ns. It uses the free square wave mode under external triggering and the trigger cycle is 1 time. The real data is shown in the figure. Figure 8 ;

[0068] The first industrial computer controls the USB 6259 to lock the bias voltages of the second amplitude modulator 402 , the third amplitude modulator 403 , and the fourth amplitude modulator 701 ; and to read the feedback signal of the first photodetector 703 to lock the signal light field intensity to the required intensity.

[0069] Receiving end: The pulse generator 15 uses ASG 8100, the second controller 18 uses an industrial personal computer, the second multi-function input / output card 17 uses PCIe 6259, the third multi-function input / output card 19 uses PCI 6115, and the first balanced homodyne detector 1604 uses a time-domain balanced homodyne detector;

[0070] The second industrial computer controls PCIe 6259 to generate multi-channel analog voltage and digital voltage signals, and at the same time receives feedback signals from the second photodetector 1302; the analog voltage signal and feedback signal are used to control the dynamic polarization control transpose 11 to complete the locking of the polarization state of the signal light field and the local oscillator light field passing through the quantum channel 10; the locked signal light field and the local oscillator light field are re-divided into the signal light field and the local oscillator light field by the optical fiber polarization beam splitter 12; after the local oscillator light field passes through the 50 / 50 polarization-maintaining optical fiber coupler and the second photodetector 1302, it generates the electrical pulse signal required for clock recovery, which is used to trigger ASG 8100 to generate a two-channel delayed synchronous clock signal, and the pulse width and delay are controlled by the second industrial computer 18; wherein, the pulse signal output by channel one is input to PCIe6259 to generate the modulation signal required for random switching of the measurement basis, modulate the phase of the local oscillator light field passing through the second phase modulator 14, and the pulse signal output by channel two is input to PCI In 6115, the electrical pulse signal output by the time-domain balanced homodyne detector is synchronized and aligned to ensure accurate measurement and acquisition of the peak value of the output electrical pulse signal; the time-domain balanced homodyne detector can receive the signal light field and the local oscillator light field, complete the measurement of the orthogonal components of the signal light field, and output the corresponding electrical pulse signal, whose peak value is linearly related to the orthogonal component.

[0071] The second industrial computer controls the PCI 6115. The input pulse signal corresponds one-to-one with the peak value of the electrical pulse signal output by the time-domain balanced homodyne detector, ensuring synchronization and alignment. Upon receiving the first clock signal, the second industrial computer begins collecting the first peak signal of the electrical pulse, continuing until the entire data block is collected. This process is hardware synchronization and does not require subsequent software algorithms for synchronization. The second industrial computer then reads the data from the PCI 6115.

[0072] The first industrial computer at the transmitting end and the second industrial computer at the receiving end are connected via a classical channel 20 to complete data screening, parameter estimation, data coordination, privacy amplification, and key generation in the process of quantum key distribution.

[0073] The transmitter sends a data block with 50K pulses. Each data block contains 500 data packets, each of which contains 100 pulses, consisting of 24 test pulses, 16 noise pulses, and 60 data pulses. Therefore, each 50K data block contains only 30K of modulated data. The test pulses are used to calculate the current phase, while the data pulses contain the modulated data. The test pulses consist of three types of pulses, with eight pulses of each type. The amplitude modulation data (r) follows a Rayleigh distribution, while the phase modulation data (θ) follows a uniform distribution.

[0074] The base clock and modulation signal are sent to the TFG 2944A through the first industrial computer, and then the three channels are closed through the command line statement. Then the receiving end runs the acquisition program, and when there is no input of the acquisition clock, the first industrial computer can control the PCI 6115 to be in the empty acquisition state. At this time, the channel output of the TFG 2944A is opened through the command line statement, and the channel starts to output data. When the first acquisition clock signal is input, the PCI 6115 is in the acquisition state, and starts to acquire the first data peak value of the time domain balanced homodyne detector output pulse. After acquiring 10M data, it is automatically stopped. The current phase value of the receiving end receiving data is set as The average of the voltage values measured by the receiving end on the orthogonal X component of the three test pulses is recorded as U0, U2, and U4. The current phase calculation formula is as follows:

[0075]

[0076]

[0077]

[0078]

[0079] Figure 9 The phase space diagram of the test pulse and the physical quantity measured by using the test pulse. After random modulation, the sending end can be modulated into a Gaussian modulation coherent state, and the conversion relationship is x A = rcosθ. 10M data X B is acquired at the receiving end, and then a current phase value is calculated every 50k data packet n∈N + and n∈[1, 200], 200 current phase values are calculated, and then the data x A of the sending end is rotated by a current phase to obtain a group of data x B '

[0080]

[0081] The size of the rotated data X B ' is 200*50k=10M, and the correlation degree is calculated with the received data. In order to test the timing and stability of the system, data reception is performed every 20 minutes, a total of 12 groups of data are acquired, and the correlation degree of the rotation transformation of the data of each time is calculated. The first 30k modulation data and the 180th 30k modulation data of each group of data are selected for correlation degree calculation, and the results are shown in the following table:

[0082]

[0083]

[0084] From the results in the above table, we can see that the maximum correlation between the data sent by the transmitter and the data received by the receiver is stable at above 0.95.

[0085] Under collective attack, the security key rate of the sender and receiver is

[0086] K col =βI AB -χ BE

[0087] β is the coordination efficiency. col >0, indicating that key distribution is unconditionally secure; if K col <0, it means that the key distribution is not secure and there are security risks.

[0088] When the receiving end adopts balanced zero-beat detection, the mutual information between the sending end and the receiving end I AB Expressed as

[0089]

[0090] The noise introduced by the detector is χ hom =[(1-η)+υ el ] / η, the channel noise is The total system noise is T is the channel transmittance, ε is the channel additional noise, η is the detection efficiency, V A is the modulation variance at the transmitter, υ el is the electronic noise of the detector.

[0091] Eve steals information BE Under collective attack, the Holevo bound is defined as

[0092] Before the receiving end measures S(ρ E )=S(ρ AB )=g(λ1)+g(λ2)

[0093] After receiving end measurement

[0094]

[0095]

[0096] Under collective attack, channel transmittance T, additional noise ε, and the mixed covariance matrix between the transmitter and receiver (before measurement at the receiver):

[0097]

[0098] Where I2 is the two-dimensional identity matrix, σ z =diag(1,-1) is the Pauli matrix. Related functions

[0099] Let α=V,β=T(V+χ line ), Where V = V A +1. The covariance matrix eigenvalues ​​λ1 and λ2 satisfy:

[0100]

[0101] S(ρ AB )=g(λ1)+g(λ2)

[0102]

[0103] Under balanced zero-beat detection,

[0104]

[0105]

[0106] To calculate the security key rate, the additional noise must be normalized to the unit of shot noise. Then the modulation variance of the transmitter, the electronic noise variance, the balanced zero-beat detector noise, the channel noise, and the system noise also change with the shot noise variance. Substituting the above parameters into the above equation, the key rate can be obtained. Figure 10 As shown in FIG, the additional noise and key rate of the system for collecting different data blocks are calculated under a fixed loss of 10 dB.

[0107] The above-described embodiments merely represent specific implementation examples of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art could make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A continuous variable quantum key distribution method based on hardware synchronization, characterized in that: The following steps are involved: In the transmitting end: a first controller (1) controls an arbitrary waveform generator (2) to synchronously output arbitrary waveforms of three channels; Channel 1 outputs a clock signal to a digital pulse generator (3) for triggering the digital pulse generator (3) to generate a multi-channel pulse signal. The pulse signal generates a signal light field and a local oscillation light field after passing through a pulse light generating device (4); Channel 2 outputs an amplitude modulation signal to a first amplitude modulator (5); Channel 3 outputs a phase modulation signal to a first phase modulator (6); The signal light field passes through the first amplitude modulator (5), the first phase modulator (6), and the first signal adjustment device (7) and is transmitted to a fiber polarization combiner (8), and is combined with the local oscillation light field to form a quantum signal, which is then transmitted to a receiving end through a quantum channel (10); The first controller (1) controls the pulse width, delay and triggering mode of the multi-channel pulses output by the digital pulse generator (3); The first controller (1) controls the first multifunctional input / output card (9) to lock the bias voltages of the pulse light generating device (4), each amplitude modulator in the first signal adjusting device (7), and the first amplitude modulator (5), and to read the feedback signal of the first signal adjusting device (7) to lock the signal light field intensity to a required intensity; In the receiving end: a second controller (18) controls a second multifunctional input / output card (17) to generate multi-channel analog voltage and digital voltage signals, and simultaneously receives a feedback signal from a second signal adjustment device (13); the analog voltage signal and the feedback signal are used to control a dynamic polarization control transposition (11) to complete the locking of the polarization states of the signal light field and the local oscillator light field passing through the quantum channel (10); the locked signal light field and the local oscillator light field are re-divided into a signal light field and a local oscillator light field through a fiber polarization beam splitter (12); after the local oscillator light field passes through the second signal adjustment device (13), an electrical pulse signal required for clock recovery is generated, which is used to trigger a pulse generator (15) to generate a two-channel delayed synchronous clock signal , the pulse width and delay of the clock signal are controlled by the second controller (18); wherein, the clock signal output by channel one is input to the second multifunctional input / output card (17), generating a modulation signal required for randomly switching the measurement base, modulating the phase of the local oscillator light field passing through the second phase modulator (14), and the clock signal output by channel two is input to the third multifunctional input / output card (19), and is synchronized and aligned with the electric pulse signal output by the detection device (16) to ensure accurate measurement and collection of the peak value of the output electric pulse signal; the detection device (16) completes the measurement of the orthogonal component of the signal light field by receiving the signal light field and the local oscillator light field, and outputs the corresponding electric pulse signal, whose peak value is linearly related to the orthogonal component; The second controller (18) controls the third multifunctional input / output card (19), and the input pulse signal corresponds to the peak value of the electric pulse signal output by the detection device (16) in a one-to-one manner, and is synchronized and aligned. When the first clock signal is received, the first electric pulse peak signal can be collected until the collection of the entire data block is completed. This process is hardware synchronization and does not require subsequent software algorithm synchronization. Afterwards, the second controller (18) reads data from the third multifunctional input / output card (19); A first controller (1) at the transmitting end and a second controller (18) at the receiving end are connected via a classical channel (20) and are used to complete data screening, parameter estimation, data coordination, privacy amplification, and key generation in the process of quantum key distribution.

2. The continuous variable quantum key distribution method based on hardware synchronization according to claim 1, characterized in that: The pulse light generating device (4) comprises a fiber laser (401), a second amplitude modulator (402), a third amplitude modulator (403), and a first polarization-maintaining fiber coupler (404); The second amplitude modulator (402) and the third amplitude modulator (403) are cascaded between the fiber laser (401) and the first polarization-maintaining fiber coupler (404), and are respectively connected to the digital pulse generator (3), and are used to generate pulsed light with a high extinction ratio under the drive of the electrical pulse signal output by the digital pulse generator (3); the first polarization-maintaining fiber coupler (404) splits the pulsed light into a signal light field and a local oscillator light field.

3. The continuous variable quantum key distribution method based on hardware synchronization according to claim 1, characterized in that: The first signal adjustment device (7) comprises a fourth amplitude modulator (701), a second polarization-maintaining fiber coupler (702), a first photodetector (703), a first polarization-maintaining fiber (704), and an adjustable optical attenuator (705); The fourth amplitude modulator (701) is used to control the intensity of the test pulse; the second polarization-maintaining fiber coupler (702) and the first photodetector (703) are used to output an electrical pulse signal for feedback to the first multifunctional input / output card (9); the first polarization-maintaining fiber (704) delays the pulse light of the signal light field at the transmitting end for time division multiplexing; and the adjustable optical attenuator (705) is used to attenuate the signal light field intensity to a suitable intensity.

4. The continuous variable quantum key distribution method based on hardware synchronization according to claim 3 is characterized in that: The second signal adjustment device (13) comprises a third polarization-maintaining fiber coupler (1301), a second photodetector (1302), and a second polarization-maintaining fiber (1303); The third polarization-maintaining fiber coupler (1301) separates a portion of the local oscillation light field, and generates an electrical pulse signal for recovering the clock through the second photodetector (1302). The remaining portion of the light field is delayed through the second polarization-maintaining fiber (1303). The second polarization-maintaining fiber (1303) corresponds to the first polarization-maintaining fiber (704) to ensure that the signal light field and the local oscillation light field reach the detection device (16) at the same time.

5. The continuous variable quantum key distribution method based on hardware synchronization according to claim 1, characterized in that: The detection device (16) comprises a first polarizer (1601), a second polarizer (1602), a 50 / 50 fiber-coupled beam splitter (1603), and a first balanced homodyne detector (1604); The first polarizer (1601), the 50 / 50 fiber-coupled beam splitter (1603), and the first balanced homodyne detector (1604) are connected in sequence; the second polarizer (1602), the 50 / 50 fiber-coupled beam splitter (1603), and the first balanced homodyne detector (1604) are connected in sequence; The first polarizer (1601) and the second polarizer (1602) are used to improve the polarization extinction ratio of the signal light field and the local oscillator light field respectively; the first balanced homodyne detector (1604) adopts a time domain detector and is used to detect the orthogonal components of the signal light field.

6. The continuous variable quantum key distribution method based on hardware synchronization according to claim 1, characterized in that: The detection device (16) comprises a first polarizer (1601), a second polarizer (1602), a 90° optical mixer (1605), a second balanced homodyne detector (1606), and a third balanced homodyne detector (1607); The input end of the 90° optical mixer (1605) is connected to the first polarizer (1601) and the second polarizer (1602) respectively, and the output end is connected to the second balanced homodyne detector (1606) and the third balanced homodyne detector (1607) respectively; The first polarizer (1601) and the second polarizer (1602) are respectively used to improve the polarization extinction ratio of the signal light field and the local oscillator light field; the second balanced homodyne detector (1606) and the third balanced homodyne detector (1607) use time domain detectors to detect the orthogonal components of the signal light field.

Images