A quantum key distribution system and method

Abstract

The present disclosure relates to a quantum key distribution system, comprising a sending end and a receiving end; a seawater channel is arranged between the sending end and the receiving end; the sending end comprises a quantum optical signal generation device, a first system control device, a first wavelength division multiplexer, a second wavelength division multiplexer, a synchronous optical signal laser, a first classical optical signal laser, a first polarization beam splitter, a first classical optical signal detector and a first expansion mirror; the receiving end comprises a quantum optical signal detection device, a second system control device, a third wavelength division multiplexer, a fourth wavelength division multiplexer, a second classical optical signal laser, a second polarization beam splitter, a synchronous optical signal detector, a second classical optical signal detector and a second expansion mirror. The quantum secret key distribution system provided by the embodiment of the present disclosure introduces classical optical communication into the quantum secret key distribution system, so that the quantum secret key distribution process can be free from the constraint of the cable, can adapt to the demand of the water channel free space, and makes the air-sea cross-medium and underwater quantum secret key distribution system practically feasible.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of quantum communication, and in particular to a quantum key distribution system and method. BACKGROUND

[0002] Quantum key distribution uses photons to carry information for key distribution, and based on the basic principles of quantum mechanics, quantum key distribution has higher security. Since the first quantum key distribution protocol was proposed, quantum key distribution has made great progress in theory and experiment.

[0003] In the atmosphere and optical fiber channel, quantum key distribution has taken a big step towards practicality and industrialization. As one of the important channels for information transmission, the development of underwater quantum key distribution technology has important significance for the secure transmission of information of underwater vehicles, secure collection of underwater data, and other scenarios that require encryption communication underwater. However, in the face of the large loss of the seawater channel, the traditional low-repetition-frequency quantum optical signal generation and the use of cables as a classical information channel are difficult to meet the requirements. In order to realize real-time secure communication in the marine environment, it is necessary and urgent to research a set of high-speed all-optical seawater channel decoy state quantum key distribution system. SUMMARY

[0004] The present disclosure provides a quantum key distribution system and method, which can realize secure and secret real-time communication in an underwater environment.

[0005] According to a first aspect of an embodiment of the present disclosure, a quantum key distribution system is provided, comprising a sending end and a receiving end;

[0006] A seawater channel is arranged between the sending end and the receiving end;

[0007] The sending end comprises a quantum optical signal generation device, a first system control device, a first wavelength division multiplexer, a second wavelength division multiplexer, a synchronous optical signal laser, a first classical optical signal laser, a first polarization beam splitter, a first classical optical signal detector, and a first expansion lens;

[0008] The receiving end comprises a quantum optical signal detection device, a second system control device, a third wavelength division multiplexer, a fourth wavelength division multiplexer, a second classical optical signal laser, a second polarization beam splitter, a synchronous optical signal detector, a second classical optical signal detector, and a second expansion lens;

[0009] The first system control device is connected with the quantum optical signal generation device, the synchronization optical signal laser, the first classical optical signal laser and the first classical optical signal detector respectively; the quantum optical signal emitted by the quantum optical signal generation device and the synchronization optical signal emitted by the synchronization optical signal laser pass through the first wavelength division multiplexer and the second wavelength division multiplexer in sequence, and finally pass through the first beam expander to be emitted to the seawater channel; the horizontal polarization classical optical signal emitted by the first classical optical signal laser passes through the first polarization beam splitter and the second wavelength division multiplexer in sequence, and finally passes through the first beam expander to be emitted to the seawater channel; the first classical optical signal detector receives the vertical polarization classical optical signal from the seawater channel which passes through the first beam expander, the second wavelength division multiplexer and the first polarization beam splitter in sequence.

[0010] The second system control device is connected with the quantum optical signal detection device, the second classical optical signal laser, the synchronization optical signal detector and the second classical optical signal detector respectively; the quantum optical signal detection device and the synchronization optical signal detector receive the quantum optical signal and the synchronization optical signal from the seawater channel which pass through the second beam expander, the third wavelength division multiplexer and the fourth wavelength division multiplexer in sequence; the second classical optical signal detector receives the horizontal polarization classical optical signal from the seawater channel which passes through the second beam expander, the third wavelength division multiplexer and the second polarization beam splitter in sequence; the vertical polarization classical optical signal emitted by the second classical optical signal laser passes through the second polarization beam splitter and the third wavelength division multiplexer in sequence, and finally passes through the second beam expander to be emitted to the seawater channel.

[0011] The wavelengths of the optical pulses corresponding to the quantum optical signal, the synchronization optical signal and the classical optical signal are in the seawater blue-green window of 450nm to 550nm.

[0012] Preferably, the quantum optical signal generation device comprises a decoy state light source module and an encoding module.

[0013] The decoy state light source module comprises four decoy state light sources, each of which is provided with a power supply circuit, a laser driver circuit, a laser temperature control circuit, a semiconductor laser and a semiconductor refrigerator.

[0014] The output end of the power supply circuit is connected with the input end of the laser driver circuit and the input end of the laser temperature control circuit respectively, the output end of the laser driver circuit is connected with the input end of the semiconductor laser, and the output end of the laser temperature control circuit is connected with the input end of the semiconductor refrigerator; the semiconductor laser is connected with the semiconductor refrigerator.

[0015] The first system control device is connected with the four decoy state light sources of the quantum optical signal generation device.

[0016] Preferably, the encoding module comprises a first beam splitter, a third polarization beam splitter and a fourth polarization beam splitter.

[0017] The quantum optical signal emitted by the first decoy state light source of the four decoy state light sources passes through a first mirror and is combined with the quantum optical signal emitted by the second decoy state light source through the third polarization beam splitter; the quantum optical signal emitted by the fourth decoy state light source of the four decoy state light sources passes through a second mirror and is combined with the quantum optical signal emitted by the third decoy state light source through the fourth polarization beam splitter.

[0018] A first fiber coupler and a first half-wave plate are sequentially arranged between the first beam splitter and the third polarization beam splitter; a second half-wave plate, a second fiber coupler and a third half-wave plate are sequentially arranged between the first beam splitter and the fourth polarization beam splitter.

[0019] An adjustable attenuator is arranged between the four decoy state light sources and the encoding module.

[0020] Preferably, the quantum optical signal detection device comprises a second beam splitter, a first single-photon detector, a second single-photon detector, a third single-photon detector and a fourth single-photon detector; the input end of the second beam splitter is connected with a filter.

[0021] The quantum optical signal is divided into two beams of quantum optical signals through the second beam splitter, one of which passes through the fourth half-wave plate and a fifth polarization beam splitter in sequence and is collected by the first single-photon detector and the second single-photon detector; the other passes through a sixth polarization beam splitter and is collected by the third single-photon detector and the fourth single-photon detector; the first single-photon detector, the second single-photon detector, the third single-photon detector and the fourth single-photon detector are connected with the second system control device.

[0022] Preferably, the first system control device comprises a first FPGA chip, a first power module, a random number chip and a first host computer post-processing module; the first FPGA chip is connected with the first power module, the random number chip, the first host computer post-processing module and the quantum optical signal generation device, respectively.

[0023] Preferably, the first FPGA chip comprises a first FPGA control module and a first host computer communication module, the first power module and the random number chip are connected with the first FPGA control module, and the first host computer communication module is connected with the first host computer post-processing module.

[0024] Preferably, the second control system comprises a second FPGA chip, a second power module, a second host computer post-processing module and a delay chip; the second FPGA chip is connected with the second power module, the second host computer post-processing module and the delay chip respectively.

[0025] Preferably, the second FPGA chip comprises a second FPGA control module and a second host computer communication module, the second power module is connected with the second FPGA control module, and the second host computer communication module is connected with the second host computer post-processing module.

[0026] According to a second aspect of the embodiments of the present disclosure, a quantum key distribution method is provided, characterized in that the data format of the quantum key comprises 39 bits of information, including 35 bits of key count information, 2 bits of decoy state information, 1 bit of base selection information and 1 bit of key information, and the method comprises:

[0027] The receiving end establishes a time sequence relationship with the sending end in response to the synchronization optical signal sent by the sending end, and generates a gating signal corresponding to the quantum optical signal;

[0028] The receiving end determines the arrangement order of the first quantum optical signal based on the synchronization optical signal and the gating signal in response to the first quantum optical signal sent by the sending end, and determines the optimal sampling time based on the gating signal;

[0029] The sending end generates a synchronization optical signal and a second quantum optical signal, sends the synchronization optical signal and the second quantum optical signal to the receiving end, and encodes and stores the second quantum optical signal based on the arrangement order;

[0030] The receiving end acquires the synchronization optical signal and the second quantum optical signal, processes the synchronization optical signal and the second quantum optical signal to obtain an initial key, and sends the key count information and the base selection information of the initial key to the sending end;

[0031] The sending end acquires the initial key information, compares the initial key information with a base based on the second quantum optical signal, processes the initial key to generate a screened key if the initial key information meets a preset detection condition, sends the key count information and the decoy state information of the screened key to the receiving end, and publishes a preset number of key information for error code estimation, so as to determine whether there is eavesdropping;

[0032] If there is no eavesdropping, the sending end and the receiving end respectively perform error correction and privacy amplification processing on the screened key to generate a final quantum key.

[0033] Preferably, the first quantum optical signal is a horizontal polarization optical signal in a fixed signal state, and the second quantum optical signal is a random polarization optical signal containing a signal state, a decoy state or a vacuum state.

[0034] The technical solutions provided by the embodiments of the present disclosure bring at least the following beneficial effects:

[0035] The quantum key distribution system provided by the embodiments of the present disclosure introduces classical optical communication into the quantum key distribution system, so that the quantum key distribution process can be free from the constraint of cables, can adapt to the requirements of water channels and free space, and makes the air-sea cross-medium and underwater quantum key distribution system practically feasible; the semiconductor laser is used as a laser light source and has two input channels of modulation signals, according to the requirements of the decoy state protocol, each channel is continuously adjustable to the semiconductor laser, so that the average photon number of each pulse of the signal state and the decoy state optical pulse can be adjusted respectively, and the integration degree of the system is improved; the FPGA is used to complete the random emission, detection and basis operation of photons, the host computer is used to complete the post-processing operation, a higher basis rate is allowed, and the photon distribution, basis operation and post-processing process are allowed to be performed in parallel.

[0036] It should be understood that the above general description and the following detailed description are only exemplary and explanatory, and cannot limit the present disclosure. BRIEF DESCRIPTION OF DRAWINGS

[0037] The accompanying drawings incorporated in the specification and forming a part of the specification illustrate embodiments consistent with the present disclosure and, together with the description, serve to explain the principles of the present disclosure, and do not constitute an undue limitation on the present disclosure.

[0038] Figure 1 is a structural schematic diagram of a quantum key distribution system according to an exemplary embodiment;

[0039] Figure 2 is a structural schematic diagram of a signal generation device according to an exemplary embodiment;

[0040] Figure 3 is a structural schematic diagram of a decoy state light source according to an exemplary embodiment;

[0041] Figure 4 is a structural schematic diagram of a quantum optical signal detection device according to an exemplary embodiment;

[0042] Figure 5 is a structural schematic diagram of a first system control device according to an exemplary embodiment;

[0043] Figure 6 is a structural schematic diagram of a second control system according to an exemplary embodiment;

[0044] Figure 7 A flow diagram of quantum key distribution according to an example embodiment is shown in FIG. 1.

[0045] Figure 8 A timing diagram of a synchronization optical signal and a quantum optical signal according to an example embodiment is shown in FIG. 2.

[0046] Figure 9 A key data format diagram according to an example embodiment is shown in FIG. 3. DETAILED DESCRIPTION

[0047] In order to make the ordinary person skilled in the art better understand the technical solutions of the present disclosure, the technical solutions in the embodiments of the present disclosure will be described clearly and completely below in conjunction with the drawings. It should be noted that the terms "first", "second" and the like in the specification and claims of the present disclosure and the above drawings are used to distinguish similar objects, and do not necessarily describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances, so that the embodiments of the present disclosure described herein can be implemented in an order other than those illustrated or described herein. The implementation described in the following example embodiments does not represent all implementations consistent with the present disclosure. Rather, they are merely examples of devices and methods consistent with some aspects of the present disclosure as detailed in the appended claims.

[0048] The embodiments of the present disclosure provide a quantum key distribution system, as shown in FIG. 1, which includes a sending end and a receiving end, wherein a seawater channel is arranged between the sending end and the receiving end. Figure 1

[0049] In the present embodiment, the sending end includes a quantum optical signal generation device 101, a first system control device 102, a first wavelength division multiplexer 103, a second wavelength division multiplexer 104, a synchronization optical signal laser 105, a first classical optical signal laser 106, a first polarization beam splitter 107, a first classical optical signal detector 108, and a first expansion lens 109.

[0050] ​In practical application, the first system control device 102 is connected with the quantum optical signal generating device 101, the synchronous optical signal laser 105, the first classical optical signal laser 106 and the first classical optical signal detector 108 respectively; the quantum optical signal generating device 101 and the synchronous optical signal laser 105 are connected with the first expansion mirror 109 through the first wavelength division multiplexer 103 and the second wavelength division multiplexer 104 in sequence, and the first classical optical signal laser 106 and the first classical optical signal detector 108 are connected with the first expansion mirror 109 through the first polarization beam splitter 107 and the second wavelength division multiplexer 104 in sequence. The quantum optical signal of the sending end can be transmitted through the transmission of the first wavelength division multiplexer 103 and the second wavelength division multiplexer 104 in sequence, enter the first expansion mirror 109 and then enter the seawater channel; the synchronous optical signal emitted by the synchronous optical signal laser 105 can be reflected by the first wavelength division multiplexer 103 and then transmitted by the second wavelength division multiplexer 104, enter the first expansion mirror 109 and then enter the seawater channel; the horizontal polarization classical optical signal emitted by the first classical optical signal laser 106 can pass through the first polarization beam splitter 107, be reflected by the second wavelength division multiplexer 104 after transmission, enter the first expansion mirror 109 and then enter the seawater channel; in addition, the classical optical signal from the receiving end can be received by the first expansion mirror 109, be reflected by the second wavelength division multiplexer 104 and then be collected by the first classical optical signal detector 108 after being reflected by the first polarization beam splitter 107.

[0051] On the other hand, the receiving end comprises a quantum optical signal detection device 110, a second system control device 111, a third wavelength division multiplexer 112, a fourth wavelength division multiplexer 113, a second classical optical signal laser 114, a second polarization beam splitter 115, a synchronous optical signal detector 116, a second classical optical signal detector 117 and a second expansion mirror 118.

[0052] In practical application, the second system control device 111 is connected with the quantum optical signal detection device 110, the second classical optical signal laser 114, the synchronous optical signal detector 116 and the second classical optical signal detector 117 respectively; the quantum optical signal detection device 110 and the synchronous optical signal detector 116 are connected with the second expansion mirror 118 through the fourth wavelength division multiplexer 113 and the third wavelength division multiplexer 112 in sequence, and the second classical optical signal laser 114 and the second classical optical signal detector 117 are connected with the second expansion mirror 118 through the second polarization beam splitter 115 and the third wavelength division multiplexer 112 in sequence.

[0053] The quantum light signal from the sending end can be shrunk by the second beam expander 118, and then pass through the third wavelength division multiplexer 112 and the fourth wavelength division multiplexer 113, and be collected by the quantum light signal detector 110. The synchronization light signal from the sending end can be shrunk by the second beam expander 118, be transmitted by the third wavelength division multiplexer 112, and be reflected by the fourth wavelength division multiplexer 113, and be collected by the synchronization light signal detector 116. The classical light signal from the sending end can be shrunk by the second beam expander 118, be reflected by the third wavelength division multiplexer 112, and then be transmitted by the second polarization beam splitter 115, and be collected by the second classical light signal detector 117. The vertically polarized classical light signal emitted by the second classical light signal laser 114 is reflected by the second polarization beam splitter 115, reflected by the third wavelength division multiplexer 112, and then enters the second beam expander 118 and the seawater channel.

[0054] In an optional embodiment, the classical light signal is a bidirectional signal. The classical light signal emitted by the sending end is emitted by the first classical light signal laser 106, and is horizontally polarized light. The classical light signal emitted by the receiving end is emitted by the second classical light signal laser 114, and is vertically polarized light. This makes the bidirectional classical light signal share a channel and avoid mutual interference, greatly simplifying the optical path. It should be noted that the information transmitted by the classical light signal mainly includes key information of the sending end and the receiving end, error correction information and error checking information.

[0055] In practical applications, the wavelengths of the quantum light signal, the synchronization light signal and the classical light signal are selected in the seawater blue-green window of 450 nm to 550 nm. On this basis, the interval between the wavelengths can be as large as possible, and the scheme of quantum light signal light pulse 450 nm, classical light signal light pulse 488 nm and synchronization light signal pulse 520 nm can be used.

[0056] In an optional embodiment, as shown in Figure 2 The signal generation device includes a decoy state light source 201 module and an encoding module.

[0057] In this embodiment, the decoy state light source 201 module includes four decoy state light sources 201. Each decoy state light source 201 is provided with a power supply circuit 301, a laser driver circuit 302, a laser temperature control circuit 303, a semiconductor laser 304 and a semiconductor cooler 305. The structure of the decoy state light source 201 is as shown in Figure 3

[0058] ​In practical application, the output end of the power supply circuit 301 is connected with the input end of the laser driver circuit 302 and the input end of the laser temperature control circuit 303 respectively, the output end of the laser driver circuit 302 is connected with the input end of the semiconductor laser 304, and the output end of the laser temperature control circuit 303 is connected with the input end of the semiconductor refrigerator 305; the semiconductor laser 304 is connected with the semiconductor refrigerator 305; the first system control device is connected with the four decoy state light sources 201 of the quantum optical signal generation device. In an optional embodiment, the semiconductor laser 304 can be composed of a 450nm laser diode, an aluminum heat dissipation shell and a temperature sensing resistor.

[0059] The laser driver circuit 302 can drive the semiconductor laser 304 to emit pulsed laser, has two independent modulation signal input channels, the two modulation channels can trigger the semiconductor laser 304 respectively, and the intensity of the light pulse triggered by each channel can be continuously adjusted, so as to meet the adjustment requirement of different light pulse intensity and realize the adjustment of different average photon numbers of the signal state, the decoy state and the vacuum state in the decoy state protocol. The laser temperature control circuit 303 controls the semiconductor refrigerator 305 to heat or cool the semiconductor laser 304 by reading the temperature sensing resistor data installed on the semiconductor laser 304, so as to keep the semiconductor laser 304 working stably at the design temperature and realize the output of stable power and stable wavelength. The power supply circuit 301 can convert the 12V direct current provided by the direct current power supply into direct current power with different voltage values, so as to meet the power requirement of each circuit submodule in the decoy state light source 201.

[0060] In the embodiment, the encoding module includes a first beam splitter 202, a third polarization beam splitter 203 and a fourth polarization beam splitter 204.

[0061] In practical application, a first optical fiber coupler 205 and a first half-wave plate 206 are sequentially arranged between the first beam splitter 202 and the third polarization beam splitter 203; a second half-wave plate 207, a second optical fiber coupler 208 and a third half-wave plate 209 are sequentially arranged between the first beam splitter 202 and the fourth polarization beam splitter 204. Among them, the third polarization beam splitter 203 is connected with the first decoy state light source and the second decoy state light source of the four decoy state light sources 201, and a first reflector 210 is arranged between the third polarization beam splitter 203 and the first decoy state light source; the fourth polarization beam splitter 204 is connected with the third decoy state light source and the fourth decoy state light source of the four decoy state light sources 201, and a second reflector 211 is arranged between the fourth polarization beam splitter 204 and the fourth decoy state light source; an adjustable attenuator is arranged between the four decoy state light sources 201 and the encoding module.

[0062] The quantum light emitted by the first decoy state light source of the four decoy state light sources 201 is combined with the quantum light emitted by the second decoy state light source through the first mirror 210 and the third polarizing beam splitter 203; the quantum light emitted by the fourth decoy state light source of the four decoy state light sources is combined with the quantum light emitted by the third decoy state light source through the second mirror 211 and the fourth polarizing beam splitter 204;

[0063] Based on the above, the function of the encoding module is to generate four different quantum polarization states, and the four groups of decoy state light sources 201 with a wavelength of 450 nm are responsible for emitting four kinds of polarization quantum light signals under the cross base and the fork base; wherein the adjustable attenuator can attenuate the average photon number of each pulse of the light pulse emitted by the decoy state light source 201 to the single photon level.

[0064] For the cross base, the horizontally polarized light is combined with the vertically polarized light through the first mirror 210 and the third polarizing beam splitter 203, and then collected into a polarization maintaining fiber by the first fiber coupler 205 through the first half-wave plate 206; similarly, the two beams under the fork base are also combined through the second mirror 211 and the fourth polarizing beam splitter 204, and then collected into a polarization maintaining fiber by the second fiber coupler 208 through the fourth half-wave plate 207, and after exiting, the two beams are collectively rotated by 45° through the third half-wave plate 209 to obtain 45° polarized light and 135° polarized light. The two groups of orthogonally polarized light that have completed beam shaping and preliminary combination will complete the final combination through the first beam splitter 202 and then be transmitted and operated. It should be noted that the above-mentioned encoding module can include a decoy state BB84 protocol encoding module.

[0065] In an optional embodiment, as shown in Figure 4 The quantum light signal detection device includes a second beam splitter 401, a first single-photon detector 402, a second single-photon detector 403, a third single-photon detector 404, and a fourth single-photon detector 405; the input end of the second beam splitter 401 is connected with a filter.

[0066] The second beam splitter 401 is connected with the first single-photon detector 402 and the second single-photon detector 403 in sequence through a fourth half-wave plate 406 and a fifth polarizing beam splitter 407, and is connected with the third single-photon detector 404 and the fourth single-photon detector 405 through a sixth polarizing beam splitter 408; the first single-photon detector 402, the second single-photon detector 403, the third single-photon detector 404, and the fourth single-photon detector 405 are all connected with a second system control device.

[0067] The quantum light signal is split into two beams of quantum light by the second beam splitter 401, one of which is sequentially passed through the fourth half-wave plate 406 and the fifth polarization beam splitter 407, and collected by the first single-photon detector 402 and the second single-photon detector 403; the other beam of quantum light signal is collected by the third single-photon detector 404 and the fourth single-photon detector 405 through the sixth polarization beam splitter 408;

[0068] In practical applications, the quantum light signal detection device can be built according to the BB84 protocol and internally integrated with a filter corresponding to the wavelength of the quantum light signal. The quantum light signal reaching the quantum light signal detection device is randomly transmitted or reflected by the second beam splitter 401. If the quantum light signal is transmitted, it is split by the fourth half-wave plate 406 and the fifth polarization beam splitter 407, and the two beams of light signal obtained are collected by the first single-photon detector 402 and the second single-photon detector 403, respectively; if the quantum light signal is reflected, it is split by the sixth polarization beam splitter, and the two beams of light signal obtained are collected by the third single-photon detector 404 and the fourth single-photon detector 405, respectively.

[0069] In an optional embodiment, as shown in Figure 5 The first system control device includes a first FPGA chip 501, a first power module 502, a random number chip 503, and a first host computer post-processing module 504; the first FPGA chip 501 is connected with the first power module 502, the random number chip 503, the first host computer post-processing module 504, and the quantum light signal generation device, respectively.

[0070] The first FPGA chip 501 includes a first FPGA control module 505 and a first host computer communication module 506, the first power module 502 and the random number chip 503 are connected with the first FPGA control module 505, and the first host computer communication module 506 is connected with the first host computer post-processing module 504.

[0071] The first FPGA control module 505 includes a laser control module 505, a first base module, a first classical light signal transmission module, a first classical light signal receiving module, and a first serial port module. The first base module is connected with the laser control module 505, the first classical light signal transmission module, the first classical light signal receiving module, and the first serial port module, respectively.

[0072] In an optional embodiment, as shown in Figure 6 The second control system includes a second FPGA chip 601, a second power module 602, a second host computer post-processing module 603, and a delay chip 604; the second FPGA chip 601 is connected with the second power module 602, the second host computer post-processing module 603, and the delay chip 604, respectively.

[0073] The second FPGA chip 601 comprises a second FPGA control module 605 and a second host computer communication module 606, the second power module 602 is connected with the second FPGA control module 605, and the second host computer communication module 606 is connected with the second host computer post-processing module 603.

[0074] The second FPGA control module 605 comprises a photon reading and synchronization module, a second base pair module, a second classical optical signal transmitting module, a second classical optical signal receiving module and a second serial port module.

[0075] The quantum key distribution system provided by the embodiment of the present disclosure introduces classical optical communication into the quantum key distribution system, so that the quantum key distribution process can be free from the constraint of cables, can adapt to the demand of water channel free space, and makes the air-sea cross-medium and underwater quantum key distribution system practically feasible; the laser diode is used as a laser light source and has two input channels of modulation signals, according to the requirement of the decoy state protocol, each channel is continuously adjustable to the laser diode, the average photon number of each pulse of the signal state and the decoy state optical pulse can be adjusted respectively, and the integration degree of the system is improved; the FPGA is used to complete the random emission, detection and base operation of photons, the host computer is used to complete the post-processing operation, a higher base rate is allowed, and the photon distribution, base operation and post-processing process can be performed in parallel.

[0076] The embodiment of the present disclosure provides a quantum key distribution method, as shown in the method comprises S701-S706. Figure 7 S701, the receiving end establishes a time sequence relationship with the sending end in response to the synchronization optical signal sent by the sending end, and generates a gate signal corresponding to the quantum optical signal.

[0077] S702, the receiving end determines the arrangement order of the first quantum optical signal based on the synchronization optical signal and the gate signal in response to the first quantum optical signal sent by the sending end, and determines the optimal sampling time based on the gate signal.

[0078] S703, the sending end generates the synchronization optical signal and the second quantum optical signal, sends the synchronization optical signal and the second quantum optical signal to the receiving end, and encodes and stores the second quantum optical signal based on the arrangement order.

[0079] S704, the receiving end acquires the synchronization optical signal and the second quantum optical signal, processes the synchronization optical signal and the second quantum optical signal to obtain an initial key, and sends the key count bit information and the base selection bit information of the initial key to the sending end.

[0080] S705, the sending end acquires initial key information, and performs basis comparison on the initial key information based on the second quantum optical signal. If the initial key information meets a preset detection condition, the initial key is processed to generate a screened key, and key count bit information and decoy state information bit information of the screened key are sent to the receiving end, and a preset number of key bit information is disclosed for error code estimation, so as to determine whether there is eavesdropping.

[0081] S706, if there is no eavesdropping, the sending end and the receiving end respectively perform error correction and privacy amplification processing on the screened key to generate a final quantum key.

[0082] If there is eavesdropping, the key is discarded.

[0083] First of all, it should be pointed out that in the embodiment, the data format of the quantum key is 39 bits, including 35 key count bits, 2 decoy state information bits, 1 base selection bit and 1 key bit. The whole process is divided into two stages of receiving and transmitting timing synchronization and generating key generation, and the quantum signal is divided into first quantum signal and second quantum signal according to the same timing characteristics.

[0084] The laser control module controls the synchronization optical signal laser and the first classical optical signal laser to emit light according to the transmission timing requirements of the synchronization optical signal and the quantum optical signal. First, 80*1024 groups of synchronization optical signal synchronization optical signal and corresponding horizontal polarization state quantum optical signal (i.e. first quantum optical signal) are sent to the receiving end to complete synchronization, then the random number of the random number chip is read to send random quantum state signal at a frequency of 50MHz, and the quantum optical signal is cached according to the key encoding logic.

[0085] In the embodiment, the transmission timing requirements of the synchronization optical signal and the quantum optical signal are that: using 5MHz synchronization optical signal, in each synchronization optical signal period, after sending a synchronization optical signal, 8 quantum optical signals of 50MHz are sent with an interval of 20ns. The timing diagram of the synchronization optical signal and the quantum optical signal is shown in Figure 8

[0086] Among them, the random number modulated quantum optical signal refers to that the random number chip can generate 4-bit random number at high rate, the first two bits control the signal state of the quantum optical signal, and the ratio of the signal state, the decoy state and the vacuum state is 2:1:1; the last two bits control the polarization state of the quantum optical signal, and the total emission ratio of the four polarization states of horizontal polarization H, vertical polarization V, 45° polarization P and 135° polarization M is 1:1:1:1.

[0087] ​The key encoding logic refers to: in order to ensure the accuracy of the base process, the transmitting and receiving parties encode each quantum optical signal. The count bit is composed of 32-bit synchronous optical signal count bit and 3-bit quantum optical signal count bit, the synchronous optical signal count bit is obtained by the FPGA chip synchronous optical signal pulse of the transmitting and receiving parties, and the quantum optical signal count bit is obtained by the synchronous calibrated number of gate signal pulses. The 2-bit decoy state information, 1-bit base selection bit and 1-bit key bit are determined by the random number chip. Since the receiving end cannot identify different states, the receiving end key has no decoy state information bit. The key data format diagram is as shown in Figure 9

[0088] The photon reading and synchronization module completes the transmitting and receiving synchronization process with the help of the random number chip and the synchronous optical signal, and then buffers the quantum optical signal detected by the detector according to the key encoding logic.

[0089] The establishment of the timing and synchronization process refers to that the photon reading and synchronization module generates a gate signal for collecting quantum optical signals with the help of the FPGA phase-locked loop IP core and the synchronous optical signal. Each 1024 synchronous optical signals form a group, and the receiving end obtains the pulse count of the horizontal polarization state according to the optical pulses obtained by the quantum optical signal detection module using the gate signal. The high-precision delay chip called by the module can realize the time movement of the synchronous optical signal with a precision of 0.25 ns. For a quantum optical signal with a width of 20 ns, the gate signal needs 80 steps to traverse. After each group of synchronous optical signals is received, the delay amount is increased, and the number of received photons at this delay amount is recorded. The receiving end FPGA chip fixes the delay amount corresponding to the maximum number of received photons, and determines the arrangement order of the quantum optical signal (i.e. the first quantum optical signal) through the statistical quantity of the number of photons under the fixed group of gate signals, to ensure the encoding of subsequent signals.

[0090] In order to facilitate understanding, the embodiments of the present disclosure take the high-speed all-optical underwater decoy state quantum key distribution scene as an example to describe the quantum key distribution system and method provided by the embodiments of the present disclosure. In the high-speed all-optical underwater decoy state quantum key distribution scene, the key distribution steps of the transmitting end and the receiving end are as follows:

[0091] Step 1, establishment of timing relationship.

[0092] The upper computer of the transmitting end and the receiving end issues a start instruction. At this time, the system control device of the transmitting end and the receiving end starts to work, the transmitting end emits synchronous optical pulses through the synchronous optical signal laser, the synchronous optical signal is collected by the synchronous optical signal detector in the receiving end through the water channel, and is converted into an electrical pulse signal and transmitted to the receiving end control module. The receiving end FPGA chip uses the received electrical signal to complete the phase-locked loop phase locking through the internal programmed timing logic circuit, establishes the timing relationship between the transmitting and receiving ends, and generates a gate signal with the same frequency and duty cycle as the quantum optical signal through frequency multiplication. ​

[0093] Step 2, completion of the synchronization scheme.

[0094] After the transmission of a synchronization optical signal is completed, the sending end transmits eight quantum optical signals of horizontal polarization states using the quantum optical signal generation module, and every 1024 synchronization optical signals form a group. The receiving end obtains the pulse count of the horizontal polarization state according to the light pulses obtained by the quantum optical signal detection module using the gate signal. The delay precision of the high-precision delay chip of the receiving end is 0.25 ns, and for a quantum optical signal of 50M frequency, the gate signal needs 80 steps to traverse. After the transmission of each group of signals is completed, the delay amount is increased, and the number of received photons at the delay amount is recorded. The receiving end FPGA chip fixes the delay amount corresponding to the maximum number of received photons, and determines the arrangement order of the quantum optical signal through the statistical amount of the number of photons under each group of gate signals, to ensure the encoding of subsequent signals.

[0095] Step 3, transmission and reception of quantum optical signals.

[0096] After synchronization is completed, the sending end continues to transmit synchronization optical signals and quantum optical signals. The FPGA chip of the sending end reads the random number of the random number chip, modulates the quantum optical signal generation module at a rate of 50M, and generates quantum optical signals of random states (signal state, decoy state, vacuum state), random polarization states (H, V, P, M). The FPGA chip encodes and stores each quantum optical signal, and the encoding consists of count bits, decoy state information bits, base selection bits and key bits.

[0097] The synchronization optical signal detector of the receiving end receives the synchronization optical signal, and the quantum optical signal is collected by the quantum optical signal detection module. The receiving end FPGA chip encodes the count bits according to the count of the detected synchronization optical signal and quantum optical signal, encodes the base selection bits and key bits according to different detectors, and stores the results. The key is transmitted to the classical optical signal transmission module.

[0098] Step 4, generation of a screened key.

[0099] After the key is generated, the receiving end first feeds back information to the sending end through classical communication, and the communication protocol used by the classical communication is OOK protocol. The count bits of the received key and the base selection bits are sent through a classical optical signal laser. The sending end receives the classical optical signal from the receiving end through a classical optical signal detector, and compares the key count bits in the storage module in the sending end FPGA chip one by one. If the key count bits in the storage module in the sending end FPGA chip can be corresponded and the base selection bits are correct, it is calculated as a code. If not, it is directly discarded. Since only data with correct base selection bits is sent, there is no need to send the base selection bits again. The base selection bit position is replaced by the key enable bit, and is set to 1 with a probability of 20%. If the bit is 1, the key bit is published and sent to the receiving end. If it is 0, the key bit is forced to be 0. The coded count bits, decoy state information bits, key enable bits, and key bits are transmitted to the receiving end through a classical optical signal laser. The receiving end codes and counts the code rate, and calculates the error rate according to the published key. The codes of the sending end and the receiving end are called screened keys.

[0100] It should be noted that steps 3 and 4 are repeated. After both parties code 6144 bits, the codes are sent to the host computer through the respective host computer communication modules for post-processing. The key is continuously generated when sent to the host computer.

[0101] Step 5, complete post-processing and generate the final secure key.

[0102] The host computer module of the FPGA will block the data and add a packet header for sending. For different types of data, the packet header is different. In the sending end, if the host computer post-processing module identifies that the packet header is the character specified by the screened key, LDPC encoding is performed, and a 384 byte check sub is generated to send the receiving end through the classical optical signal laser controlled by the sending end FPGA chip. At the same time, the number of key groups is counted. If there are 256 groups, the host computer post-processing module performs error checking and private amplification, and sends the hash value generated by the error checking to the receiving end through the classical optical signal laser controlled by the sending end FPGA chip. If it is information from the receiving end whether the error checking is successful, the host computer post-processing module detects whether it is successful, and decides whether to keep the key. If it is successful, the compressed key is written to the hard disk, and the sending end key generation is successful.

[0103] At the receiving end, if the upper computer post-processing module identifies the post-screening key, it is stored in the buffer area, waiting for the check sub from the sending end to perform LDPC decoding; if the upper computer post-processing module identifies the LDPC check sub, it performs LDPC decoding and increases the count; if the upper computer post-processing module identifies the state information, it judges the circuit board state according to the state information and calculates the code rate and the bit error rate; if the upper computer post-processing module identifies the error check hash value from the sending end, it performs error check and private amplification on the existing key, and judges whether the generated hash value is the same as the received one from the sending end, if the same, it feeds back the information of successful error check to the sending end through the classical optical signal laser, and stores the key and writes it into the hard disk, and the receiving end key generation is successful.

[0104] Other embodiments of the disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the features disclosed herein. The disclosure is intended to cover any variations, uses or adaptations of the disclosure following, in general, the principles of the disclosure and including such features that are evident to those skilled in the art to which the disclosure pertains. The specification and examples are to be regarded as illustrative only, and the true scope and spirit of the disclosure are indicated by the following claims.

[0105] It should be understood that the present disclosure is not limited to the precise construction that has been described above and shown in the accompanying drawings, and that various modifications and changes can be made without departing from the scope thereof. The scope of the present disclosure is limited only by the claims that follow.

Claims

1. A quantum key distribution system, characterized by, The system comprises a sending end and a receiving end; A seawater channel is arranged between the sending end and the receiving end; The sending end comprises a quantum optical signal generation device, a first system control device, a first wavelength division multiplexer, a second wavelength division multiplexer, a synchronous optical signal laser, a first classical optical signal laser, a first polarization beam splitter, a first classical optical signal detector and a first beam expander; The receiving end comprises a quantum optical signal detection device, a second system control device, a third wavelength division multiplexer, a fourth wavelength division multiplexer, a second classical optical signal laser, a second polarization beam splitter, a synchronous optical signal detector, a second classical optical signal detector and a second beam expander; The first system control device is connected with the quantum optical signal generation device, the synchronous optical signal laser, the first classical optical signal laser and the first classical optical signal detector respectively; the quantum optical signal emitted by the quantum optical signal generation device and the synchronous optical signal emitted by the synchronous optical signal laser pass through the first wavelength division multiplexer and the second wavelength division multiplexer in sequence, and finally pass through the first beam expander to exit into the seawater channel; the horizontally polarized classical optical signal emitted by the first classical optical signal laser passes through the first polarization beam splitter and the second wavelength division multiplexer in sequence, and finally passes through the first beam expander to exit into the seawater channel; the first classical optical signal detector receives the vertically polarized classical optical signal from the seawater channel, which passes through the first beam expander, the second wavelength division multiplexer and the first polarization beam splitter in sequence; The second system control device is connected with the quantum optical signal detection device, the second classical optical signal laser, the synchronous optical signal detector and the second classical optical signal detector respectively; the quantum optical signal detection device and the synchronous optical signal detector receive the quantum optical signal and the synchronous optical signal from the seawater channel, which pass through the second beam expander, the third wavelength division multiplexer and the fourth wavelength division multiplexer in sequence; the second classical optical signal detector receives the horizontally polarized classical optical signal from the seawater channel, which passes through the second beam expander, the third wavelength division multiplexer and the second polarization beam splitter in sequence; the vertically polarized classical optical signal emitted by the second classical optical signal laser passes through the second polarization beam splitter and the third wavelength division multiplexer in sequence, and finally passes through the second beam expander to exit into the seawater channel; The wavelengths of the optical pulses corresponding to the quantum optical signal, the synchronous optical signal and the classical optical signal are in the seawater blue-green window of 450nm to 550nm; The quantum optical signal generation device comprises a decoy state light source module and an encoding module; The decoy state light source module comprises four decoy state light sources, each of which is provided with a power supply circuit, a laser driver circuit, a laser temperature control circuit, a semiconductor laser and a semiconductor refrigerator; The output end of the power supply circuit is connected with the input end of the laser driver circuit and the input end of the laser temperature control circuit respectively, the output end of the laser driver circuit is connected with the input end of the semiconductor laser, and the output end of the laser temperature control circuit is connected with the input end of the semiconductor refrigerator. The first system control device is connected with the four decoy state light sources of the quantum optical signal generation device.

2. The quantum key distribution system of claim 1, wherein, The encoding module comprises a first beam splitter, a third polarization beam splitter and a fourth polarization beam splitter. The quantum optical signal emitted by the first decoy state light source of the four decoy state light sources and the quantum optical signal emitted by the second decoy state light source pass through the third polarization beam splitter after being combined by the first reflector; the quantum optical signal emitted by the fourth decoy state light source of the four decoy state light sources and the quantum optical signal emitted by the third decoy state light source pass through the fourth polarization beam splitter after being combined by the second reflector. A first fiber coupler and a first half-wave plate are sequentially arranged between the first beam splitter and the third polarization beam splitter; a second half-wave plate, a second fiber coupler and a third half-wave plate are sequentially arranged between the first beam splitter and the fourth polarization beam splitter. An adjustable attenuator is arranged between the four decoy state light sources and the encoding module.

3. The quantum key distribution system of claim 1, wherein, The quantum optical signal detection device comprises a second beam splitter, a first single-photon detector, a second single-photon detector, a third single-photon detector and a fourth single-photon detector; the input end of the second beam splitter is connected with a filter; The quantum optical signal passes through the second beam splitter to be divided into two quantum optical signals; one of the quantum optical signals passes through a fourth half-wave plate and a fifth polarization beam splitter in sequence and is collected by the first single-photon detector and the second single-photon detector; the other quantum optical signal passes through a sixth polarization beam splitter and is collected by the third single-photon detector and the fourth single-photon detector; the first single-photon detector, the second single-photon detector, the third single-photon detector and the fourth single-photon detector are connected with the second system control device.

4. The quantum key distribution system of claim 1, wherein, The first system control device comprises a first FPGA chip, a first power module, a random number chip and a first host computer post-processing module; the first FPGA chip is connected with the first power module, the random number chip, the first host computer post-processing module and the quantum optical signal generation device respectively.

5. The quantum key distribution system of claim 4, wherein, The first FPGA chip comprises a first FPGA control module and a first host computer communication module; the first power module and the random number chip are connected with the first FPGA control module; and the first host computer communication module is connected with the first host computer post-processing module.

6. The quantum key distribution system of claim 1, wherein, The second system control device comprises a second FPGA chip, a second power module, a second host computer post-processing module and a delay chip; the second FPGA chip is connected with the second power module, the second host computer post-processing module and the delay chip respectively.

7. The quantum key distribution system of claim 6, wherein, The second FPGA chip comprises a second FPGA control module and a second host computer communication module, the second power module is connected with the second FPGA control module, and the second host computer communication module is connected with the second host computer post-processing module.

8. An underwater quantum key distribution method applied to the quantum key distribution system according to any one of claims 1-7, characterized in that, The data format of the quantum key comprises 39 bits of information, including 35 bits of key count information, 2 bits of decoy state information, 1 bit of base selection information and 1 bit of key information. The receiving end establishes a timing relationship with the sending end in response to the synchronization optical signal sent by the sending end, and generates a gating signal corresponding to the quantum optical signal; The receiving end determines the arrangement order of the first quantum optical signal based on the synchronization optical signal and the gating signal, and determines the optimal sampling time based on the gating signal in response to the first quantum optical signal sent by the sending end; The sending end generates a synchronization optical signal and a second quantum optical signal, sends the synchronization optical signal and the second quantum optical signal to the receiving end, and encodes and stores the second quantum optical signal based on the arrangement order; The receiving end acquires the synchronization optical signal and the second quantum optical signal, processes the synchronization optical signal and the second quantum optical signal to obtain an initial key, and sends the key count information and the base selection information of the initial key to the sending end; The sending end acquires the initial key information, compares the initial key information with a base based on the second quantum optical signal, processes the initial key if the initial key information meets a preset detection condition to generate a screened key, sends the key count information and the decoy state information of the screened key to the receiving end, and publishes a preset number of key information for error estimation to determine whether there is eavesdropping; If there is no eavesdropping, the sending end and the receiving end respectively perform error correction and privacy amplification processing on the screened key to generate a final quantum key.

9. The method of claim 8, wherein, The first quantum optical signal is a horizontal polarization optical signal in a fixed signal state, and the second quantum optical signal is a random polarization optical signal containing a signal state, a decoy state or a vacuum state.

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