Quantum key distribution method and system

Abstract

The present disclosure provides a quantum key distribution method and system, relating to the field of quantum communication technology. The method includes using a clock amplification module to process pulse seed light transmitted by a measurement end through a classical channel to obtain a clock electrical signal and a pump optical signal; inputting the clock electrical signal into a signal source to output a clock reference signal; based on the clock reference signal, using a labeled single-photon source module to process the pump optical signal to obtain a labeled single photon and a first detection result; based on the clock reference signal, using an encoding module to process the labeled single photon to obtain an output optical pulse, and transmitting the output optical pulse to a measurement end through a quantum channel, so that the measurement end generates a second detection result based on the output optical pulse of the transmitting end and the output optical pulse of the receiving end; and generating a key distribution result based on the second detection result and the first detection result published by the measurement end.

Description

Technical Field

[0001] The present disclosure relates to the field of quantum communication technology, and more specifically, to a quantum key distribution method and system. Background Art

[0002] With the development of an information-based society, people have a higher demand for information security. Currently, the security of classical cryptographic systems relies on computational complexity. However, with the development of quantum computing, this classical encryption method will become less secure. Quantum Key Distribution (QKD) technology provides a method for establishing unconditionally secure keys between communicators. Combined with the "one-time pad" method, it can theoretically achieve unconditional information security. However, due to the open nature of the detection channel, many security vulnerabilities have been identified.

[0003] Using high-power femtosecond or picosecond mode-locked lasers in conjunction with nonlinear crystals of specific lengths to generate high-spectral-purity single-photon markers requires synchronizing two remotely located high-power femtosecond or picosecond mode-locked lasers. Existing lasers are often unsuitable for long-distance synchronization and are complex, resulting in timing jitter exceeding tens of picoseconds. Furthermore, limited by the modulator bandwidth, femtosecond or picosecond pulses are difficult to generate. Summary of the Invention

[0004] In view of this, the embodiments of the present disclosure provide a quantum key distribution method and system.

[0005] One aspect of an embodiment of the present disclosure provides a quantum key distribution method, which is applied to a transmitting end or a receiving end of a quantum key distribution system. The method includes: using a clock amplification module to process a pulse seed light transmitted by a measuring end through a classical channel to obtain a clock electrical signal and a pump optical signal; inputting the clock electrical signal into a signal source to output a clock reference signal; based on the clock reference signal, using a marked single-photon source module to process the pump optical signal to obtain a marked single photon and a first detection result; based on the clock reference signal, using an encoding module to process the marked single photon to obtain an output optical pulse, and transmitting the output optical pulse to the measuring end through a quantum channel, so that the measuring end generates a second detection result based on the output optical pulse of the transmitting end and the output optical pulse of the receiving end; and generating a key distribution result based on the second detection result and the first detection result published by the measuring end.

[0006] According to an embodiment of the present disclosure, a clock amplification module is used to process the pulse seed light transmitted by the measurement end through the classical channel to obtain a clock electrical signal and a pump light signal, including: using an optical beam splitter to process the pulse seed light to obtain a first seed light and a second seed light; using an optical amplification module to process the first seed light to obtain a pump light signal; and using a photoelectric detection module to process the second seed light to obtain a clock electrical signal.

[0007] According to an embodiment of the present disclosure, based on a clock reference signal, a marked single-photon source module is used to process a pump light signal to obtain a marked single photon and a first detection result, including: using a spontaneous parametric down-conversion method to convert the pump light signal to obtain a first photon pair, wherein the first photon pair includes a first photon and a second photon that are temporally correlated; using a first polarization beam splitter to process the first photon pair to obtain a separated first photon and a second photon, wherein the separated first photon represents the marked single photon; based on the clock reference signal, using a first single-photon detector to process the separated second photon to obtain The first detection result; wherein, before converting the pump light signal by using the spontaneous parametric down-conversion method, it also includes: using the frequency doubling module to process the pump light signal to obtain the frequency-doubled pump light signal, so that the pump light signal meets the conditions for spontaneous parametric down-conversion; wherein, before using the first polarization beam splitter to process the first photon pair, it also includes: using the optical filter to process the first photon pair to obtain the filtered first photon pair, and using the first polarization beam splitter to process the filtered first photon pair, wherein the optical filter is configured to isolate the pump light in the first photon pair and improve the spectral purity of the first photon pair.

[0008] According to an embodiment of the present disclosure, based on a clock reference signal, a marked single-photon source module is used to process a pump light signal to obtain a marked single photon and a first detection result, including: using a spontaneous four-wave mixing method to convert the pump light signal to obtain a second photon pair, wherein the second photon pair includes a third photon and a fourth photon that are temporally correlated; using a dense wavelength division multiplexer to process the second photon pair to obtain a separated third photon and a fourth photon, wherein the separated third photon represents the marked single photon; based on the clock reference signal, using a second single-photon detector to process the separated fourth photon to obtain the first detection result.

[0009] According to an embodiment of the present disclosure, based on a clock reference signal, a coding module is used to process a marked single photon to obtain an output optical pulse, including: using a first polarization controller to process the marked single photon to obtain a first optical signal; using a first intensity modulator to process the first optical signal to obtain a second optical signal; using a second polarization controller to process the second optical signal to obtain a third optical signal; using a second polarization beam splitter to process the third optical signal to obtain a fourth optical signal and a fifth optical signal; based on the clock reference signal, using a first phase modulator to process the fourth optical signal to obtain a sixth optical signal; using a polarization beam combiner to process the fifth optical signal and the sixth optical signal to obtain a seventh optical signal; and using a third polarization controller to process the seventh optical signal to obtain an output optical pulse.

[0010] According to an embodiment of the present disclosure, based on a clock reference signal, a coding module is used to process a marked single photon to obtain an output optical pulse, including: using a fourth polarization controller to process the marked single photon to obtain a first pulse signal; based on the clock reference signal, using a second intensity modulator to process the first pulse signal to obtain a second pulse signal; based on the clock reference signal, using a circulator to input the second pulse signal into a Sagnac ring to output a third pulse signal and a fourth pulse signal; based on the clock reference signal, using a second phase modulator to process the third pulse signal to obtain a fifth pulse signal; using a first optical coupler to process the fifth pulse signal and the sixth pulse signal to obtain a seventh pulse signal, wherein the sixth pulse signal is obtained by processing the fourth pulse signal by the circulator; using a fifth polarization controller to process the seventh pulse signal to obtain an output optical pulse.

[0011] Another aspect of the embodiments of the present disclosure provides a quantum key distribution method, which is applied to the measurement end of a quantum key distribution system, the method comprising: generating pulse seed light using a seed laser; sending pulse seed light to a transmitting end and a receiving end respectively using a classical channel, so that both the transmitting end and the receiving end generate output optical pulses, wherein the output optical pulse is obtained by processing a labeled single photon using an encoding module based on a clock reference signal, the labeled single photon is obtained by processing a pump optical signal using a labeled single photon source module based on the clock reference signal, the clock reference signal is obtained by inputting a clock electrical signal into a signal source, and the clock electrical signal and the pump optical signal are obtained by processing the pulse seed light using a clock amplification module; processing the output optical pulses transmitted by the transmitting end and the receiving end using a detection module to obtain a second detection result, and publishing the second detection result to the transmitting end and the receiving end, so that the transmitting end and the receiving end generate a key distribution result based on the second detection result and the first detection result, wherein the first detection result is obtained by processing the pump optical signal using the labeled single photon source module.

[0012] Another aspect of an embodiment of the present disclosure provides a user end of a quantum key distribution system, comprising: a clock amplification module, for processing pulse seed light transmitted by a measuring end through a classical channel to obtain a clock electrical signal and a pump optical signal; a signal source, for processing the clock electrical signal to obtain a clock reference signal; a marked single-photon source module, for processing the pump optical signal based on the clock reference signal to obtain a marked single photon and a first detection result; an encoding module, for processing the marked single photon based on the clock reference signal to obtain an output optical pulse, and transmitting the output optical pulse to the measuring end through a quantum channel, so that the measuring end generates a second detection result based on the output optical pulse of the transmitting end and the output optical pulse of the receiving end; and a generation module, for generating a key distribution result based on the second detection result and the first detection result published by the measuring end.

[0013] Another aspect of the embodiments of the present disclosure provides a measurement end of a quantum key distribution system, comprising: a seed laser, for generating pulse seed light, and using a classical channel to send the pulse seed light to a transmitting end and a receiving end respectively, so that both the transmitting end and the receiving end generate output optical pulses, wherein the output optical pulse is obtained by processing a labeled single photon using an encoding module based on a clock reference signal, the labeled single photon is obtained by processing a pump optical signal using a labeled single photon source module based on the clock reference signal, the clock reference signal is obtained by inputting a clock electrical signal into a signal source, and the clock electrical signal and the pump optical signal are obtained by processing the pulse seed light using a clock amplification module; a detection module, for processing the output optical pulses transmitted by the transmitting end and the receiving end, obtaining a second detection result, and publishing the second detection result to the transmitting end and the receiving end, so that the transmitting end and the receiving end generate a key distribution result based on the second detection result and the first detection result, wherein the first detection result is obtained by processing the pump optical signal using the labeled single photon source module.

[0014] Another aspect of an embodiment of the present disclosure provides a quantum key distribution system, including: a measurement end, used to send pulse seed light to a transmitter and the receiving end through a classical channel; a classical channel, used to transmit the pulse seed light of the measurement end to the transmitter and the receiving end; a transmitter, constructed based on the above-mentioned user end; a receiving end, constructed based on the above-mentioned user end; wherein, both the transmitter and the receiving end are used to generate a first detection result and an output light pulse based on the pulse seed light; a quantum channel, used to transmit the output light pulse generated by the transmitter and the receiving end to the measurement end, so that the measurement end generates a second detection result based on the output light pulse, and publishes the second detection result to the transmitter and the receiving end, so that the transmitter and the receiving end generate a key distribution result based on the first detection result and the second detection result.

[0015] According to the embodiments of the present disclosure, by using the same pulse seed light and transmitting it via optical links at the transmitting and receiving ends respectively, the jitter problem of pulse arrival time caused by electronic noise is avoided, and long-distance, low-cost, and low-time-jitter optical pulse synchronization can be achieved, providing an important basic guarantee for long-distance measurement device-independent quantum key distribution. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The above and other objects, features and advantages of the present disclosure will become more apparent through the following description of the embodiments of the present disclosure with reference to the accompanying drawings, in which:

[0017] Figure 1 A flowchart of a quantum key distribution method applied to a transmitting end or a receiving end of a quantum key distribution system according to an embodiment of the present disclosure is schematically shown;

[0018] Figure 2The flowchart of the quantum key distribution method applied to the measurement end of the quantum key distribution system according to the embodiment of the present disclosure is schematically shown;

[0019] Figure 3 A schematic diagram of a quantum key distribution method based on a spontaneous four-wave mixing source according to an embodiment of the present disclosure is schematically shown;

[0020] Figure 4 A schematic diagram of a quantum key distribution method based on a spontaneous four-wave mixing source according to an embodiment of the present disclosure is schematically shown;

[0021] Figure 5 A block diagram schematically illustrates a user terminal of a quantum key distribution system according to an embodiment of the present disclosure;

[0022] Figure 6 A block diagram schematically illustrates a measurement end of a quantum key distribution system according to an embodiment of the present disclosure; and

[0023] Figure 7 A block diagram of a quantum key distribution system according to an embodiment of the present disclosure is schematically shown. DETAILED DESCRIPTION

[0024] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present disclosure. In the detailed description below, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of the embodiments of the present disclosure. However, it is apparent that one or more embodiments may also be implemented without these specific details. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion of the concepts of the present disclosure.

[0025] The terms used herein are only for describing specific embodiments and are not intended to limit the present disclosure. The terms "comprise," "include," etc. used herein indicate the presence of the features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0026] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0027] When expressions such as "at least one of A, B and C, etc." are used, they should generally be interpreted in accordance with the meaning of the expression commonly understood by those skilled in the art (for example, "a system having at least one of A, B and C" should include but is not limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.).

[0028] Since a high-power femtosecond or picosecond mode-locked laser is used in conjunction with a nonlinear crystal of a specific length to produce a high-spectral-purity labeled single-photon source, it is necessary to synchronize two high-power femtosecond or picosecond mode-locked lasers at different locations.

[0029] Most lasers in the existing technology are not suitable for long-distance laser synchronization and are relatively complex, causing time jitter to reach more than ten picoseconds. At the same time, they are limited by the modulator bandwidth and are not easy to generate femtosecond or picosecond pulses.

[0030] In view of the above problems, the inventors found that by using the same pulse seed light and transmitting it via an optical link at the transmitting end and the receiving end respectively, the jitter problem of the pulse arrival time caused by electronic noise can be avoided.

[0031] The embodiments of the present disclosure provide a quantum key distribution method and system. The method includes using a clock amplification module to process pulsed seed light transmitted from a measurement end through a classical channel to obtain a clock electrical signal and a pump optical signal; inputting the clock electrical signal into a signal source to output a clock reference signal; based on the clock reference signal, using a labeled single-photon source module to process the pump optical signal to obtain a labeled single photon and a first detection result; based on the clock reference signal, using an encoding module to process the labeled single photon to obtain an output optical pulse, and transmitting the output optical pulse to the measurement end through a quantum channel, so that the measurement end generates a second detection result based on the output optical pulse of the transmitting end and the output optical pulse of the receiving end; and generating a key distribution result based on the second detection result and the first detection result published by the measurement end.

[0032] Figure 1 The flowchart of the quantum key distribution method applied to the transmitting end or the receiving end of the quantum key distribution system according to an embodiment of the present disclosure is schematically shown.

[0033] like Figure 1 As shown, the method includes operations S110 to S150.

[0034] In operation S110, the clock amplification module is used to process the pulse seed light transmitted by the measurement end through the classical channel to obtain a clock electrical signal and a pump light signal.

[0035] In operation S120 , a clock electrical signal is input to a signal source, and a clock reference signal is output.

[0036] In operation S130 , based on the clock reference signal, the pump light signal is processed using the labeled single photon source module to obtain a labeled single photon and a first detection result.

[0037] In operation S140, based on the clock reference signal, the coding module is used to process the labeled single photon to obtain an output optical pulse, and the output optical pulse is transmitted to the measurement end through the quantum channel, so that the measurement end generates a second detection result according to the output optical pulse of the transmitting end and the output optical pulse of the receiving end.

[0038] In operation S150, a key distribution result is generated based on the second detection result and the first detection result published by the measurement terminal.

[0039] According to an embodiment of the present disclosure, the clock electrical signal of the input signal source is used to adjust the clock of the transmitting end or the receiving end of the quantum key distribution system, so that the clocks of the transmitting end and the receiving end are synchronized, and the clock reference signals output by the transmitting end and the receiving end are consistent.

[0040] According to the embodiments of the present disclosure, the pulse seed light is outputted through the clock amplification module to obtain a pump light signal with an amplified light intensity, which can ensure that the subsequent marking single-photon source module can obtain sufficient pump power.

[0041] According to an embodiment of the present disclosure, the first detection result is used to determine whether the labeled single photon exists.

[0042] According to an embodiment of the present disclosure, the encoding module adopts the MDI protocol (measurement device independent).

[0043] According to the embodiments of the present disclosure, when the labeled single-photon source module processes the pump light signal, errors inherent in the module result in a first detection result that produces two results: valid and invalid, represented by 1 and 0, respectively. If both the transmitting and receiving ends indicate a first detection result of 1, the second detection result published by the measuring end is also 1, and the key distribution result indicates successful key transmission. If at least one of the transmitting and receiving ends indicates a first detection result of 0, the second detection result is also 0, and the key distribution result indicates invalid key transmission. Based on the key distribution result, the transmitting and receiving ends determine whether to retain the current key.

[0044] According to the embodiments of the present disclosure, by using the same pulse seed light and transmitting it via optical links at the transmitting and receiving ends respectively, the jitter problem of pulse arrival time caused by electronic noise is avoided, and long-distance, low-cost, and low-time-jitter optical pulse synchronization can be achieved, providing an important basic guarantee for long-distance measurement device-independent quantum key distribution.

[0045] According to an embodiment of the present disclosure, a clock amplification module is used to process the pulse seed light transmitted by the measurement end through the classical channel to obtain a clock electrical signal and a pump light signal, including: using an optical beam splitter to process the pulse seed light to obtain a first seed light and a second seed light; using an optical amplification module to process the first seed light to obtain a pump light signal; and using a photoelectric detection module to process the second seed light to obtain a clock electrical signal.

[0046] According to the embodiments of the present disclosure, an optical beam splitter splits the pulsed seed light into two beams. The first seed light passes through an optical amplifier module, which amplifies its intensity to ensure sufficient pump power for the subsequent labeled single-photon source module. The optical amplifier module can be an erbium-doped fiber amplifier or a semiconductor optical amplifier. This disclosure does not limit the choice of spontaneous parametric down-conversion source; those skilled in the art can make their own selection based on practical needs.

[0047] According to an embodiment of the present disclosure, the second seed light passes through the photoelectric detection module and undergoes photoelectric conversion to obtain a clock electrical signal, which is input into the signal source and used as a local clock reference to ensure synchronization between the clock and the clock electrical signal.

[0048] According to an embodiment of the present disclosure, based on a clock reference signal, a marked single photon source module is used to process a pump light signal to obtain a marked single photon and a first detection result, including:

[0049] The pump light signal is converted using a spontaneous parametric down-conversion method to obtain a first photon pair, wherein the first photon pair includes a first photon and a second photon that are temporally correlated; the first photon pair is processed using a first polarization beam splitter to obtain separated first and second photons, wherein the separated first photon represents a labeled single photon; and based on a clock reference signal, the separated second photon is processed using a first single-photon detector to obtain a first detection result.

[0050] Before the spontaneous parametric down-conversion source is used to process the pump light signal, the method further includes: converting the pump light signal using a spontaneous parametric down-conversion method to obtain a frequency-doubled pump light signal, so that the pump light signal meets the conditions for spontaneous parametric down-conversion.

[0051] Before using the first polarization beam splitter to process the first photon pair, the method further includes: using an optical filter to process the first photon pair to obtain a filtered first photon pair, and using the first polarization beam splitter to process the filtered first photon pair, wherein the optical filter is configured to isolate the pump light in the first photon pair and improve the spectral purity of the first photon pair.

[0052] According to an embodiment of the present disclosure, the frequency doubling module is used to double the frequency of the pump light signal so as to enable it to meet the conditions for spontaneous parametric down-conversion.

[0053] According to an embodiment of the present disclosure, a spontaneous parametric down-conversion source can be selected based on a type-II nonlinear crystal. After the pump light signal passes through the type-II nonlinear crystal of the spontaneous parametric down-conversion source, a first photon pair is spontaneously generated with a certain probability, and the first photon and the second photon are temporally correlated. Since a type-II spontaneous parametric down-conversion source is used, the polarizations of the generated first photon pairs are mutually orthogonal. The present disclosure does not limit the choice of the spontaneous parametric down-conversion source, and those skilled in the art can make a selection based on actual needs.

[0054] According to an embodiment of the present disclosure, the optical filter is used to isolate the pump light in the first photon pair on the one hand, and to improve the photon spectral purity of the output first photon pair on the other hand.

[0055] According to an embodiment of the present disclosure, after the first photon pair passes through the first polarization beam splitter, the first photon and the second photon are respectively output from two different output ports thereof.

[0056] According to the embodiments of the present disclosure, because the spontaneous parametric down-conversion source determines the probability of generating a first photon pair based on its own performance, there may be results where a first photon pair is generated or not generated. If the first single-photon detector receives the second photon, a first detection result of 1 indicates that the result is valid. If the first photon pair is not generated, the first single-photon detector cannot receive the second photon and a first detection result of 0 indicates that the result is invalid.

[0057] According to an embodiment of the present disclosure, based on a clock reference signal, a marked single-photon source module is used to process a pump light signal to obtain a marked single photon and a first detection result, including: using a spontaneous four-wave mixing method to convert the pump light signal to obtain a second photon pair, wherein the second photon pair includes a third photon and a fourth photon that are temporally correlated; using a dense wavelength division multiplexer to process the second photon pair to obtain a separated third photon and a fourth photon, wherein the separated third photon represents the marked single photon; based on the clock reference signal, using a second single-photon detector to process the separated fourth photon to obtain the first detection result.

[0058] According to the embodiments of the present disclosure, a spontaneous four-wave mixing source receives a pump light signal and generates a third-order nonlinear effect in its medium, generating a second photon pair. The two pump photons in the second photon pair are then spontaneously converted with a certain probability into two other photons, a third photon and a fourth photon, whose energy and momentum satisfy conservation conditions. The third and fourth photons are temporally correlated, and their summed energy equals twice the energy of the pump light signal.

[0059] According to an embodiment of the present disclosure, a dense wavelength division multiplexer can be used to separate the associated third photon and fourth photon. The central channel of the dense wavelength division multiplexer should be consistent with the central wavelength of the pump light signal, and the separated third photon and fourth photon are respectively located at the symmetrical channels on both sides of the central channel. For example, the central channel corresponds to C34 of the ITU standard (International Telecommunication Union), and the two separated photons are respectively located at C32 and C36. In addition, the dense wavelength division multiplexer also has the function of a filter, which can improve the spectral purity of the output photons to a certain extent.

[0060] According to an embodiment of the present disclosure, when the second single-photon detector receives the fourth photon, the first detection result obtained is 1, indicating that the result is valid; if the second photon pair cannot be generated, the first single-photon detector cannot receive the fourth photon, and the first detection result obtained is 0, indicating that the result is invalid.

[0061] According to an embodiment of the present disclosure, based on a clock reference signal, a coding module is used to process a marked single photon to obtain an output optical pulse, including: using a first polarization controller to process the marked single photon to obtain a first optical signal; using a first intensity modulator to process the first optical signal to obtain a second optical signal; using a second polarization controller to process the second optical signal to obtain a third optical signal; using a second polarization beam splitter to process the third optical signal to obtain a fourth optical signal and a fifth optical signal; based on the clock reference signal, using a first phase modulator to process the fourth optical signal to obtain a sixth optical signal; using a polarization beam combiner to process the fifth optical signal and the sixth optical signal to obtain a seventh optical signal; and using a third polarization controller to process the seventh optical signal to obtain an output optical pulse.

[0062] According to an embodiment of the present disclosure, the marked single photon passes through the first polarization controller and is input into the first intensity modulator. The function of the first polarization controller is to make the polarization of the marked single photon consistent with the input polarization required by the first intensity modulator to reduce loss.

[0063] According to an embodiment of the present disclosure, the function of the first intensity modulator is to modulate the light intensity of the first optical signal to obtain the light intensity required for the decoy state in the MDI protocol in the encoding module.

[0064] According to an embodiment of the present disclosure, the second polarization controller adjusts the polarization of the second optical signal output by the first intensity modulator so that both output ports of the second polarization beam splitter have light intensity output.

[0065] According to an embodiment of the present disclosure, one of the two ports of the second polarization beam splitter is first connected to the first phase modulator and then to an input port of the polarization beam combiner; the other port is directly connected to another input port of the polarization beam combiner. The polarization beam combiner can then combine the light from these two input ports into two orthogonal polarization directions.

[0066] According to the embodiment of the present disclosure, the polarization direction of the fifth optical signal is defined as H, the polarization direction of the fourth optical signal is defined as V, and the phase modulation magnitude of the first phase modulator is φ. Then, the polarization state of the output light of the polarization beam combiner is Set the modulation phase φ to four discrete fixed phases 0, By adjusting the third polarization controller to a suitable angle, four BB84 states can be obtained as output optical pulses at the output port of the encoding module, namely

[0067] According to an embodiment of the present disclosure, based on a clock reference signal, a coding module is used to process a marked single photon to obtain an output optical pulse, including: using a fourth polarization controller to process the marked single photon to obtain a first pulse signal; based on the clock reference signal, using a second intensity modulator to process the first pulse signal to obtain a second pulse signal; based on the clock reference signal, using a circulator to input the second pulse signal into a Sagnac ring to output a third pulse signal and a fourth pulse signal; based on the clock reference signal, using a second phase modulator to process the third pulse signal to obtain a fifth pulse signal; using a first optical coupler to process the fifth pulse signal and the sixth pulse signal to obtain a seventh pulse signal, wherein the sixth pulse signal is obtained by processing the fourth pulse signal by the circulator; using a fifth polarization controller to process the seventh pulse signal to obtain an output optical pulse.

[0068] According to an embodiment of the present disclosure, the marked single photon passes through the fourth polarization controller and is input into the first intensity modulator. The function of the fourth polarization controller is to make the polarization of the marked single photon consistent with the input polarization required by the second intensity modulator to reduce loss.

[0069] According to the embodiments of the present disclosure, the circulator can realize unidirectional transmission of high-frequency signal energy by controlling the electromagnet to transmit along a certain circular direction, thereby playing the role of being independent and isolated from each other.

[0070] According to an embodiment of the present disclosure, the second pulse signal is input from the first port of the circulator, output from the second port of the circulator, and enters the Sagnac ring.

[0071] According to an embodiment of the present disclosure, the Sagnac loop decomposes the second pulse signal into a third pulse signal and a fourth pulse signal, and allows them to circulate in opposite directions within the same loop for one cycle and then meet.

[0072] Figure 2 Schematically shows a flow chart of a quantum key distribution method applied to a measurement end of a quantum key distribution system according to an embodiment of the present disclosure

[0073] like Figure 2 As shown, another aspect of the embodiment of the present disclosure provides a quantum key distribution method, which is applied to a measurement end of a quantum key distribution system. The method includes operations S210 to S230:

[0074] In operation S210 , pulse seed light is generated using a seed laser.

[0075] In operation S220, a pulse seed light is sent to the transmitting end and the receiving end respectively using a classical channel, so that both the transmitting end and the receiving end generate output optical pulses, wherein the output optical pulse is obtained by processing the marked single photon using the encoding module based on the clock reference signal, the marked single photon is obtained by processing the pump optical signal using the marked single photon source module based on the clock reference signal, the clock reference signal is obtained by inputting the clock electrical signal into the signal source, and the clock electrical signal and the pump optical signal are obtained by processing the pulse seed light using the clock amplification module.

[0076] In operation S230, the detection module is used to process the output optical pulses transmitted by the transmitting end and the receiving end to obtain a second detection result, and the second detection result is announced to the transmitting end and the receiving end so that the transmitting end and the receiving end generate a key distribution result based on the second detection result and the first detection result, wherein the first detection result is obtained by processing the pump light signal using the marked single-photon source module.

[0077] According to an embodiment of the present disclosure, the seed laser may be a mode-locked pulse seed laser.

[0078] According to an embodiment of the present disclosure, the detection module processes the output optical pulses transmitted by the transmitter and receiver and publishes whether the response conditions are met as a second detection result. If the first detection result of both the transmitter and receiver is 1, the second detection result published by the measurement end is 1, indicating that the key distribution result is successful. If at least one of the transmitter and receiver is 0, the second detection result is 0, indicating that the current key distribution result is invalid. The transmitter and receiver determine whether the current key is retained based on the key distribution result.

[0079] Figure 3 A schematic diagram of a quantum key distribution method based on a spontaneous four-wave mixing source according to an embodiment of the present disclosure is schematically shown.

[0080] like Figure 3As shown in the figure, the measurement end uses a seed laser to generate pulsed seed light and sends the pulsed seed light to the transmitter and receiver respectively. The transmitter and receiver have the same structure and process the signal in the same way. There is no signal transmission between the transmitter and receiver.

[0081] The receiving and transmitting ends use optical beam splitters to split the pulsed seed light into two beams, generating the first seed light and the second seed light. The first seed light passes through the optical amplifier module to amplify the light intensity and generate the pump light signal. The second seed light passes through the photoelectric detection module, where it undergoes photoelectric conversion to generate a clock electrical signal. This signal is then input into the signal source and used as a local clock reference.

[0082] The frequency doubling module is used to frequency-double the pump light signal. After passing through the spontaneous parametric down-conversion source, the pump light signal spontaneously generates a first photon pair with a certain probability. After being filtered by the optical filter and passing through the first polarization beam splitter, the first and second photons of the first photon pair are output from two different output ports. The first single-photon detector receives the second photon and obtains the first detection result; the first photon serves as the marker single photon.

[0083] After the labeled single photon passes through the first polarization controller, a first optical signal is obtained and input into the first intensity modulator. The second polarization controller adjusts the polarization of the second optical signal output by the first intensity modulator to obtain a third optical signal, so that the two output ports of the second polarization beam splitter output the fourth optical signal and the fifth optical signal respectively. Of the two ports of the second polarization beam splitter, one port is first connected to the first phase modulator and then to an input port of the polarization beam combiner to obtain the sixth optical signal; the other port is directly connected to the other input port of the polarization beam combiner. The polarization beam combiner combines the fifth optical signal and the sixth optical signal into two orthogonal polarization directions to obtain a seventh optical signal. After the seventh optical signal is processed by the third polarization controller, four BB84 state pulse lights are obtained as output optical pulses.

[0084] The measurement end performs measurements in the polarization dimension and further includes a second optical coupler, a sixth polarization beam splitter, a seventh polarization beam splitter, a third single-photon detector, a fourth single-photon detector, a fifth single-photon detector, and a sixth single-photon detector. The two input ports of the second optical coupler receive the output light pulses of the receiving and transmitting ends, respectively, while the two output ports are connected to the sixth polarization beam splitter and the seventh polarization beam splitter, respectively. The two output ports of the sixth polarization beam splitter are connected to the third single-photon detector and the fourth single-photon detector, respectively. The two output ports of the seventh polarization beam splitter are connected to the fifth single-photon detector and the sixth single-photon detector, respectively. In each round of communication, the measurement end publishes the matching responses of these four detectors as the second measurement result. The receiving and transmitting ends then select the key bits to be retained based on the key distribution result.

[0085] Figure 4 A schematic diagram of a quantum key distribution method based on a spontaneous four-wave mixing source according to an embodiment of the present disclosure is schematically shown.

[0086] like Figure 4 As shown, the process for obtaining the pump optical signal and clock electrical signal is identical to the aforementioned quantum key distribution method based on a cascaded spontaneous parametric down-conversion source with a frequency multiplication module, and will not be further elaborated here. The transmitter and receiver have the same structure and are symmetrical, meaning they process the signal identically, rather than one sending and the other receiving.

[0087] A spontaneous four-wave mixing (SFWM) source receives a pump light signal, generating a third-order nonlinear effect in its medium, generating a second photon pair consisting of a third and a fourth photon. A dense wavelength division multiplexer (DWDM) separates the associated third and fourth photons. A second single-photon detector receives the fourth photon and generates the first detection result; the third photon serves as the marker single photon.

[0088] After the labeled single photon passes through the fourth polarization controller, a first pulse signal is obtained, which is input into the second intensity modulator to obtain a second pulse signal. The second pulse signal is input from the first port of the circulator, output from the second port of the circulator, and enters the Sagnac ring. The Sagnac ring decomposes the second pulse signal into a third pulse signal and a fourth pulse signal, allowing them to circulate in opposite directions within the same loop for one cycle and then meet. The third pulse signal is processed by the second phase modulator to obtain a fifth pulse signal. The sixth pulse signal is obtained by the circulator processing the fourth pulse signal. The first optical coupler processes the fifth and sixth pulse signals to obtain a seventh pulse signal. The fifth polarization controller processes the seventh pulse signal to obtain an output optical pulse.

[0089] The Sagnac ring is composed of a third optical coupler and a third phase modulator. The first port of the third optical coupler is connected to the first port of the third phase modulator, and the second port of the third optical coupler is connected to the second port of the third phase modulator. The third port of the third optical coupler is connected to the second port of the circulator, and the fourth port of the third optical coupler is connected to the second phase modulator.

[0090] The second pulse signal is incident through the third port of the third optical coupler and exits from the first and second ports of the third optical coupler, with the third and fourth pulse signals circulating in a clockwise and counterclockwise direction, respectively. Because the three-phase modulator is positioned at a non-central position within the Sagnac ring, it modulates only one of the third and fourth pulse signals during each modulation cycle. By controlling the third phase modulator, the ratio of the light intensities exiting the third and fourth ports of the third optical coupler can be controlled.

[0091] The third optical coupler and the first optical coupler can be equivalent to an unequal-arm Mach-Zehnder interferometer. According to the requirements of time-bin encoding, the quantum states that need to be adjusted are |L>, |S>, These four states correspond to the light pulse only traveling along the long arm of the Mach-Zehnder interferometer, only traveling along the short arm, and a superposition of two or more states. The third phase modulation can control the intensity of the light pulse traveling along the long and short arms, and the second phase modulator can control the phase difference between the long and short arms, thereby achieving complete modulation of the above four states. The seventh pulse signal obtained after modulation is emitted through the first optical coupler, and then the fifth polarization controller is used to perform polarization compensation in the optical fiber channel to obtain the output light pulse. Among them, all optical fiber devices are polarization-maintaining devices, and all optical fibers are single-mode polarization-maintaining fibers.

[0092] The measurement end performs measurements based on the timestamp dimension and also includes a fourth optical coupler, a seventh single-photon detector, and an eighth single-photon detector. The fourth optical coupler's two input ports receive the output light pulses from the receiving and transmitting ends, respectively, while its two output ports are connected to the seventh and eighth single-photon detectors, respectively. Bell state measurements are performed based on the response times of these two detectors. During each round of communication, the measurement end publishes the matching responses of these two detectors as the second measurement result. The receiving and transmitting ends then select the key bits to be retained based on the key distribution results.

[0093] According to an embodiment of the present disclosure, the measuring end sends a pulse seed light to the receiving end and the transmitting end. Both ends first optically amplify the pulse seed light, and then generate a first photon pair and a second photon pair through a nonlinear process. The first photon detector and the second photoelectron detector are respectively combined to obtain a labeled single photon. The present disclosure solves the synchronization problem of the labeled single photon sources of both parties in long-distance communication by sharing the pulse seed light. In addition, no electronic devices are involved in the optical transmission process, which avoids the jitter problem of the pulse arrival time caused by electronic noise, and provides the necessary conditions for realizing a low bit error rate measurement device-independent protocol.

[0094] Figure 5 A block diagram of a user end of a quantum key distribution system according to an embodiment of the present disclosure is schematically shown.

[0095] like Figure 5 As shown, the user end of the quantum key distribution system includes a clock amplification module 510, a signal source 520, a labeled single photon source module 530, an encoding module 540 and a generation module 550.

[0096] The clock amplification module 510 is used to process the pulse seed light transmitted by the measurement end through the classical channel to obtain a clock electrical signal and a pump optical signal. In one embodiment, the clock amplification module can be used to perform the operation S110 described above, which will not be repeated here.

[0097] The signal source 520 is used to process the clock electrical signal to obtain a clock reference signal. In one embodiment, the clock amplification module can be used to perform the operation S120 described above, which will not be described in detail here.

[0098] The labeled single photon source module 530 is used to process the pump light signal based on the clock reference signal to obtain the labeled single photon and the first detection result. In one embodiment, the clock amplification module can be used to perform the operation S130 described above, which will not be repeated here.

[0099] The encoding module 540 is configured to process the labeled single photons based on the clock reference signal to generate an output optical pulse. The encoding module 540 then transmits the output optical pulse to the measurement end via a quantum channel, so that the measurement end generates a second detection result based on the output optical pulse from the transmitting end and the output optical pulse from the receiving end. In one embodiment, the clock amplification module can be used to perform operation S140 described above and will not be further described here.

[0100] The generation module 550 is used to generate a key distribution result based on the second detection result and the first detection result published by the measurement terminal. In one embodiment, the clock amplification module can be used to perform the operation S150 described above, which will not be repeated here.

[0101] According to the embodiments of the present disclosure, by using the same pulse seed light and transmitting it via optical links at the transmitting and receiving ends respectively, the jitter problem of pulse arrival time caused by electronic noise is avoided, and long-distance, low-cost, and low-time-jitter optical pulse synchronization can be achieved, providing an important basic guarantee for long-distance measurement device-independent quantum key distribution.

[0102] Figure 6 A block diagram of a measurement end of a quantum key distribution system according to an embodiment of the present disclosure is schematically shown.

[0103] like Figure 6 As shown, the measurement end of the quantum key distribution system includes a seed laser 610 and a detection module 620.

[0104] The seed laser 610 is used to generate pulse seed light and use a classical channel to send the pulse seed light to the transmitting end and the receiving end respectively, so that both the transmitting end and the receiving end generate output optical pulses, wherein the output optical pulse is obtained by processing the marked single photon based on the clock reference signal using the encoding module, and the marked single photon is obtained by processing the pump optical signal based on the clock reference signal using the marked single photon source module, the clock reference signal is obtained by inputting the clock electrical signal into the signal source, and the clock electrical signal and the pump optical signal are obtained by processing the pulse seed light using the clock amplification module.

[0105] The detection module 620 is used to process the output optical pulses transmitted by the transmitting end and the receiving end, obtain a second detection result, and publish the second detection result to the transmitting end and the receiving end, so that the transmitting end and the receiving end generate a key distribution result based on the second detection result and the first detection result, wherein the first detection result is obtained by using the marked single-photon source module to process the pump light signal.

[0106] Figure 7 A block diagram of a quantum key distribution system according to an embodiment of the present disclosure is schematically shown.

[0107] like Figure 4 As shown, the quantum key distribution system includes a measurement end 600, a classical channel 710, a transmitting end 500, a receiving end 500 and a quantum channel 720.

[0108] The measuring end 600 is used to send pulse seed light to the transmitting end and the receiving end through a classical channel.

[0109] The classical channel 710 is used to transmit the pulse seed light from the measurement end to the transmitting end and the receiving end.

[0110] The transmitting end 600 and the receiving end 600 are both used to generate a first detection result and an output optical pulse according to the pulse seed light.

[0111] The quantum channel 720 is used to transmit the output optical pulses generated by the transmitting end and the receiving end to the measuring end, so that the measuring end generates a second detection result based on the output optical pulses, and publishes the second detection result to the transmitting end and the receiving end, so that the transmitting end and the receiving end generate a key distribution result based on the first detection result and the second detection result.

[0112] Those skilled in the art will appreciate that various combinations and / or combinations of features described in the various embodiments and / or claims of this disclosure may be made, even if such combinations or combinations are not explicitly described in this disclosure. In particular, various combinations and / or combinations of features described in the various embodiments and / or claims of this disclosure may be made, without departing from the spirit and teachings of this disclosure. All such combinations and / or combinations fall within the scope of this disclosure.

[0113] The embodiments of the present disclosure are described above. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of the present disclosure. Although each embodiment has been described separately above, this does not mean that the measures in each embodiment cannot be used in combination to advantage. The scope of the present disclosure is defined by the appended claims and their equivalents. Without departing from the scope of the present disclosure, those skilled in the art may make various substitutions and modifications, which should all fall within the scope of the present disclosure.

Claims

1. A quantum key distribution method, applied to a transmitting end or a receiving end of a quantum key distribution system, comprising: The clock amplifier module is used to process the pulse seed light transmitted from the measurement end through the classical channel to obtain the clock electrical signal and the pump light signal; Input the clock electrical signal into a signal source and output a clock reference signal; Based on the clock reference signal, using a labeled single-photon source module to process the pump light signal to obtain a labeled single photon and a first detection result; Based on the clock reference signal, the labeled single photon is processed using a coding module to obtain an output optical pulse, and the output optical pulse is transmitted to the measurement end through a quantum channel, so that the measurement end generates a second detection result according to the output optical pulse of the transmitting end and the output optical pulse of the receiving end; generating a key distribution result according to the second detection result and the first detection result published by the measurement terminal; The clock amplification module is used to process the pulse seed light transmitted from the measurement end through the classical channel to obtain the clock electrical signal and the pump light signal, including: Processing the pulse seed light using an optical beam splitter to obtain a first seed light and a second seed light; Processing the first seed light using an optical amplification module to obtain the pump light signal; The second seed light is processed by a photoelectric detection module to obtain the clock electrical signal.

2. The method according to claim 1, wherein Based on the clock reference signal, the pump light signal is processed using a labeled single photon source module to obtain a labeled single photon and a first detection result, including: Converting the pump light signal using spontaneous parametric down-conversion to obtain a first photon pair, wherein the first photon pair includes a first photon and a second photon that are temporally correlated; Processing the first photon pair using a first polarization beam splitter to obtain a separated first photon and a second photon, wherein the separated first photon represents the marker single photon; Based on the clock reference signal, using a first single-photon detector to process the separated second photon to obtain the first detection result; Before converting the pump light signal by using the spontaneous parametric down-conversion method, the method further includes: Processing the pump light signal using a frequency doubling module to obtain a frequency-doubled pump light signal, so that the pump light signal satisfies a condition for spontaneous parametric down-conversion; Before using the first polarization beam splitter to process the first photon pair, the method further includes: The first photon pair is processed using an optical filter to obtain a filtered first photon pair, and the filtered first photon pair is processed using the first polarization beam splitter, wherein the optical filter is configured to isolate the pump light in the first photon pair and improve the spectral purity of the first photon pair.

3. The method according to claim 1, wherein Based on the clock reference signal, the pump light signal is processed using a labeled single photon source module to obtain a labeled single photon and a first detection result, including: converting the pump light signal by using spontaneous four-wave mixing to obtain a second photon pair, wherein the second photon pair includes a third photon and a fourth photon that are temporally correlated; Processing the second photon pair using a dense wavelength division multiplexer to obtain a separated third photon and a fourth photon, wherein the separated third photon represents the marker single photon; Based on the clock reference signal, the separated fourth photon is processed using a second single-photon detector to obtain the first detection result.

4. The method according to claim 1, wherein Based on the clock reference signal, the marked single photon is processed by a coding module to obtain an output optical pulse, comprising: Processing the labeled single photon using a first polarization controller to obtain a first optical signal; Processing the first optical signal using a first intensity modulator to obtain a second optical signal; processing the second optical signal using a second polarization controller to obtain a third optical signal; Processing the third optical signal using a second polarization beam splitter to obtain a fourth optical signal and a fifth optical signal; Processing the fourth optical signal using a first phase modulator based on the clock reference signal to obtain a sixth optical signal; Processing the fifth optical signal and the sixth optical signal using a polarization beam combiner to obtain a seventh optical signal; The seventh optical signal is processed by using a third polarization controller to obtain the output optical pulse.

5. The method according to claim 1, wherein Based on the clock reference signal, the marked single photon is processed by a coding module to obtain an output optical pulse, comprising: Processing the labeled single photon using a fourth polarization controller to obtain a first pulse signal; Based on the clock reference signal, using a second intensity modulator to process the first pulse signal to obtain a second pulse signal; Based on the clock reference signal, using a circulator to input the second pulse signal into a Sagnac ring, and output a third pulse signal and a fourth pulse signal; Based on the clock reference signal, processing the third pulse signal using a second phase modulator to obtain a fifth pulse signal; Processing a fifth pulse signal and a sixth pulse signal using a first optical coupler to obtain a seventh pulse signal, wherein the sixth pulse signal is obtained by processing the fourth pulse signal by the circulator; The seventh pulse signal is processed by a fifth polarization controller to obtain the output light pulse.

6. A quantum key distribution method, applied to a measurement end of a quantum key distribution system, comprising: generating pulsed seed light using a seed laser; The pulse seed light is respectively transmitted to a transmitting end and a receiving end using a classical channel, so that both the transmitting end and the receiving end generate output optical pulses, wherein the output optical pulse is obtained by processing a labeled single photon using an encoding module based on a clock reference signal, the labeled single photon is obtained by processing a pump optical signal using a labeled single photon source module based on the clock reference signal, the clock reference signal is obtained by inputting a clock electrical signal into a signal source, and the clock electrical signal and the pump optical signal are obtained by processing the pulse seed light using a clock amplification module; Processing the output optical pulses transmitted by the transmitting end and the receiving end using a detection module to obtain a second detection result, and announcing the second detection result to the transmitting end and the receiving end, so that the transmitting end and the receiving end generate a key distribution result based on the second detection result and the first detection result, wherein the first detection result is obtained by processing the pump light signal using a labeled single-photon source module; The clock electrical signal and the pump optical signal are generated in the following manner: Processing the pulse seed light using an optical beam splitter to obtain a first seed light and a second seed light; Processing the first seed light using an optical amplification module to obtain the pump light signal; The second seed light is processed by a photoelectric detection module to obtain the clock electrical signal.

7. A user terminal of a quantum key distribution system, comprising: The clock amplifier module is used to process the pulse seed light transmitted by the measurement end through the classical channel to obtain the clock electrical signal and the pump optical signal, including: Processing the pulse seed light using an optical beam splitter to obtain a first seed light and a second seed light; Processing the first seed light using an optical amplification module to obtain the pump light signal; Processing the second seed light using a photoelectric detection module to obtain the clock electrical signal; A signal source, configured to process the clock electrical signal to obtain a clock reference signal; a marked single-photon source module, configured to process the pump light signal based on the clock reference signal to obtain a marked single photon and a first detection result; an encoding module, configured to process the labeled single photon based on the clock reference signal to obtain an output optical pulse, and transmit the output optical pulse to the measurement end through a quantum channel, so that the measurement end generates a second detection result based on the output optical pulse of the transmitting end and the output optical pulse of the receiving end; A generating module is configured to generate a key distribution result according to the second detection result and the first detection result published by the measuring terminal.

8. A measurement end of a quantum key distribution system, comprising: A seed laser, configured to generate pulsed seed light and transmit the pulsed seed light to a transmitting end and a receiving end respectively using a classical channel, so that both the transmitting end and the receiving end generate output optical pulses, wherein the output optical pulses are obtained by processing a labeled single photon using an encoding module based on a clock reference signal, the labeled single photon is obtained by processing a pump optical signal using a labeled single photon source module based on the clock reference signal, the clock reference signal is obtained by inputting a clock electrical signal into a signal source, and the clock electrical signal and the pump optical signal are obtained by processing the pulsed seed light using a clock amplification module; a detection module, configured to process the output optical pulses transmitted by the transmitting end and the receiving end to obtain a second detection result, and publish the second detection result to the transmitting end and the receiving end, so that the transmitting end and the receiving end generate a key distribution result based on the second detection result and the first detection result, wherein the first detection result is obtained by processing the pump optical signal using a labeled single-photon source module; The clock electrical signal and the pump optical signal are generated in the following manner: Processing the pulse seed light using an optical beam splitter to obtain a first seed light and a second seed light; Processing the first seed light using an optical amplification module to obtain the pump light signal; The second seed light is processed by a photoelectric detection module to obtain the clock electrical signal.

9. A quantum key distribution system, comprising: The measuring end according to claim 8, configured to send pulse seed light to the transmitting end and the receiving end through a classical channel; The classical channel is used to transmit the pulse seed light of the measuring end to the transmitting end and the receiving end; The sending end is constructed based on the user end according to claim 7; The receiving end is constructed based on the user end according to claim 7; Wherein, the transmitting end and the receiving end are both used to generate a first detection result and an output optical pulse according to the pulse seed light; A quantum channel is used to transmit the output optical pulses generated by the transmitting end and the receiving end to the measuring end, so that the measuring end generates the second detection result based on the output optical pulses, and publish the second detection result to the transmitting end and the receiving end, so that the transmitting end and the receiving end generate a key distribution result based on the first detection result and the second detection result.

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