Multi-path anti-interference quantum key distribution system

Abstract

The invention discloses a multipath anti-interference quantum key distribution system, which comprises a sending end, a receiving end and a control unit in communication connection with the receiving end and the sending end, and is characterized in that the sending end is connected with the receiving end through a reference path and m delay paths; a transmitting end encodes an optical pulse emitted in a current period based on randomly selected phase encoding, performs beam splitting on a quantum state optical pulse after phase encoding, and inputs a reference path and a randomly selected delay path in the current period respectively; the receiving end combines the quantum state light pulses output by the reference path and the delay path, detects the quantum state light pulses with enhanced interference, records the detection result of the current period and sends the detection result to the control unit, and the control unit determines the optimal delay path in the current environment. The error rate caused by noise interference is reduced through the interference design of the delay path and the reference path, and the stability of long-distance transmission is effectively guaranteed.

Description

Technical Field

[0001] The present invention belongs to the technical field of quantum key distribution, and more specifically, the present invention relates to a multi-path anti-interference quantum key distribution system. Background Art

[0002] Quantum key distribution (QKD) technology uses the principles of quantum mechanics to provide information-theoretically secure key sharing between communicating parties. Its core principle is to exploit the non-cloning property of quantum states to defend against eavesdropping attacks. The RDRPS protocol, a type of high-dimensional phase-encoded protocol, has attracted widespread attention due to its unique parameter-free monitoring and high error tolerance. In the traditional RRDPS protocol, the transmitter encodes key information using the phase difference between multiple pulses, and the receiver randomly selects two pulses for interferometry. Because an eavesdropper cannot predict the position of the selected pulses, the amount of information they can obtain is strictly limited, thus ensuring the security of the protocol. This mechanism enables the RRDPS protocol to perform well in medium- and short-distance transmission scenarios, and is particularly suitable for environments with large channel noise fluctuations.

[0003] However, as QKD technology expands into long-distance, high-security scenarios, the limitations of the traditional RRDPS protocol are gradually becoming apparent. First, its coding dimension is limited, supporting only two phase combinations (0 and π), resulting in a small key space, making it difficult to meet the key capacity and anti-cracking requirements in high-security scenarios. Second, although the RRDPS protocol has a high tolerance for random bit errors, when the fiber link experiences significant changes due to environmental factors (such as temperature fluctuations and mechanical vibration) or when there are targeted attacks (such as photon number splitting attacks), the path noise increases significantly, and the bit error rate may quickly exceed the protocol tolerance threshold, causing key generation to be interrupted. Summary of the Invention

[0004] The present invention provides a multi-path interference-resistant quantum key distribution system, aiming to improve at least one of the above problems.

[0005] The present invention is implemented as follows: a multi-path anti-interference quantum key distribution system, the system comprising:

[0006] A transmitting end and a receiving end, a control unit in communication with the receiving end and the transmitting end, wherein the transmitting end is connected to the receiving end via a reference path and m delayed paths;

[0007] The transmitting end encodes the light pulse emitted in the current cycle based on the randomly selected phase coding, splits the phase-coded quantum state light pulse, and inputs it into the reference path and the randomly selected delay path of the current cycle respectively; the receiving end combines the quantum state light pulses output by the reference path and the delay path, detects the quantum state light pulse with enhanced interference, records the detection results of the current cycle and sends them to the control unit, which determines the optimal delay path under the current environment.

[0008] Furthermore, the system also includes:

[0009] A first optical switch and a second optical switch are provided at both ends of all delay paths, and the first optical switch and the second optical switch are communicatively connected with the control unit;

[0010] The first optical switch is arranged at the transmitting end, and the beam splitter is connected to all delay paths through the first optical switch; the second optical switch is arranged at the receiving end, and the beam combiner is connected to all delay paths through the second optical switch; the control unit randomly selects a delay path based on the current cycle, and controls the first and second optical switches to switch to the randomly selected delay path.

[0011] Furthermore, the transmission time of the quantum light pulse on the reference path is L, and the transmission time on the delayed path is L+n△L, and the value of n for each delayed path is different.

[0012] Furthermore, the transmitting end includes a laser, an intensity modulator, a phase modulator, and a beam splitter connected in sequence;

[0013] The laser emits a laser pulse, the intensity of which is adjusted by an intensity modulator, and the phase of which is modulated by a phase modulator. The phase-encoded quantum state light pulse is input into a beam splitter, which splits the phase-encoded quantum state light pulse into two beams, which are input into a reference path and a randomly selected delay path respectively.

[0014] Furthermore, the receiving end includes: a beam combiner and a single photon detector SPD; the quantum state light pulses output from the reference path and the delay path are combined by the beam combiner and input into the single photon detector SPD, and the single photon detector SPD detects the interference-enhanced quantum state light pulses.

[0015] Furthermore, the control unit records the number of responses of the single-photon detector SPD when quantum state light pulses are transmitted based on the reference path and the selected delay path in each cycle, and takes the delay path with the largest number of responses of the single-photon detector SPD in a unit cycle as the optimal delay path under the current environment.

[0016] Furthermore, after determining the optimal delay path in the current environment, the first optical switch and the second optical switch are controlled to switch to the optimal delay path, and the optimal delay path and the reference path are used as the optical pulse transmission channel between the receiving end and the transmitting end in the current environment.

[0017] Furthermore, the phase modulator supports 3 to 8 phase encodings in the range of 0 to π, and the phase differences between adjacent phases are equal.

[0018] Furthermore, the value range of m is 3 to 8.

[0019] The present invention reduces the bit error rate caused by noise interference through the interference design of the delay path and the reference path, effectively ensuring the stability of long-distance transmission. In addition, multiple delay paths are designed, and the multiple delay paths are combined with the reference path. The delay path with the lowest bit error rate after combining with the reference path is determined, and the delay path and the reference path are used as the optical pulse transmission channel between the transmitting end and the receiving end to further reduce the bit error rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A schematic diagram of the structure of a multi-path interference-resistant quantum key distribution system provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0021] The specific implementation methods of the present invention will be further explained in detail below by describing the embodiments with reference to the accompanying drawings, so as to help those skilled in the art to have a more complete, accurate and in-depth understanding of the inventive concept and technical solution of the present invention.

[0022] Figure 1 A schematic diagram of the structure of a multi-path anti-interference quantum key distribution system provided in an embodiment of the present invention is provided. For ease of illustration, only the parts related to the embodiment of the present invention are shown. The system includes:

[0023] A transmitting end and a receiving end, a control unit in communication with the receiving end and the transmitting end, wherein the transmitting end is connected to the receiving end via a reference path and m delayed paths;

[0024] The transmitting end encodes the light pulse emitted in the current cycle based on the randomly selected phase code, splits the phase-coded quantum state light pulse, and inputs it into the reference path and the randomly selected delay path of the current cycle respectively; the receiving end combines the quantum state light pulses output by the reference path and the delay path, detects the quantum state light pulse with enhanced interference, records the detection results of the current cycle and sends them to the control unit. The control unit determines the optimal delay path with the least noise disturbance in the current environment based on the detection results.

[0025] The control unit or the transmitter randomly selects the phase code for optical pulse encoding in each cycle. The phase code of the optical pulse in the same cycle is the same. The control unit randomly selects the delay path for quantum state optical pulse transmission in each cycle. In the same cycle, the optical pulse is transmitted through the reference path and the randomly selected same delay path.

[0026] When there is noise interference in the reference path or the selected delay path, the phase of the quantum state light pulse of the corresponding path will be shifted. The light pulse with the phase shift will produce weakened interference with the light pulse that arrives at the combiner at the same time from another path. The light pulse after weakened interference will not be detected by the single photon detector SPD, and the phase code with noise interference will be discarded, thereby reducing the bit error rate caused by noise interference.

[0027] In an embodiment of the present invention, the transmitting end includes a laser, an intensity modulator, a phase modulator and a beam splitter connected in sequence, wherein the laser emits a laser pulse, the intensity modulator adjusts the intensity of the laser pulse and the phase modulator modulates the phase of the laser pulse, and the phase-encoded quantum state light pulse is input into the beam splitter. The beam splitter divides the encoded quantum state light pulse into two beams, which are respectively input into a reference path and a randomly selected delay path.

[0028] The receiving end includes a beam combiner and a single photon detector SPD; the quantum state light pulses output from the reference path and the delay path are combined by the beam combiner and then input into the single photon detector SPD, which records the interference-enhanced quantum state light pulses.

[0029] The laser generates continuous laser pulses with a wavelength of 1550nm, a pulse width of 100ps, and a repetition rate of 1GHz. An intensity modulator adjusts the intensity of the laser pulses, with a modulation bandwidth greater than 10GHz. A phase modulator modulates the phase of the optical pulses by applying a specific voltage signal, achieving flexible encoding of multiple phase states and transmitting the encoded quantum state optical pulses to the receiver. The phase modulator supports 3-8 phase encodings within the range of 0 to π, with equal phase differences between adjacent phases and a phase switching time of ≤1ns. An example of a phase modulator is a Mach-Zehnder interferometer (MZI) structure.

[0030] In an embodiment of the present invention, the transmission time of a quantum state light pulse on the reference path is L, and the transmission time on the delay path is L+n△L. The transmission time of the quantum state light pulse on each delay path is different, that is, the value of n is different. When the quantum state light pulse on the reference path and the quantum state light pulse on the delay path reach the combiner at the same time, interference occurs at the combiner. The delay path controls the delay time by the path length.

[0031] In an embodiment of the present invention, the system further includes:

[0032] A first optical switch and a second optical switch are provided at both ends of all delay paths. The first optical switch is provided at the transmitting end. The beam splitter is connected to all delay paths via the first optical switch. The second optical switch is provided at the receiving end. The beam combiner is connected to all delay paths via the second optical switch. The first optical switch and the second optical switch are communicatively connected to a control unit. The control unit randomly selects a delay path and controls the first optical switch and the second optical switch to switch to the randomly selected delay path. The two quantum state light pulses split by the beam splitter are transmitted to the receiving end via the reference path and the selected delay path within the current cycle.

[0033] In an embodiment of the present invention, an encoded quantum state optical pulse is transmitted to a receiving end via a reference path and a randomly selected delay path. The control unit records the number of responses of the single-photon detector (SPD) during quantum state optical pulse transmission based on the reference path and the selected delay path within each cycle. The delay path with the most responses is selected as the optimal delay path under the current environment. The optimal delay path and the reference path serve as the optical pulse transmission channel between the receiving end and the transmitting end under the current environment. That is, the control unit controls the first optical switch and the second optical switch to switch to the optimal delay path, and the optimal delay path and the reference path serve as the optical pulse transmission channel between the receiving end and the transmitting end under the current environment. A large number of responses of the single-photon detector (SPD) within a cycle indicates a low probability of phase offset of the optical pulse on the reference path and the selected delay path.

[0034] The present invention reduces the bit error rate caused by noise interference through the interference design of the delay path and the reference path, effectively ensuring the stability of long-distance transmission. In addition, multiple delay paths are designed, and the multiple delay paths are combined with the reference path. The delay path with the lowest bit error rate after combining with the reference path is determined, and the delay path and the reference path are used as the optical pulse transmission channel between the transmitting end and the receiving end to further reduce the bit error rate.

[0035] The present invention has been described exemplarily. Obviously, the specific implementation of the present invention is not limited to the above-mentioned method. As long as various non-substantial improvements are made using the method concept and technical solution of the present invention, or the concept and technical solution of the present invention are directly applied to other occasions without improvement, they are all within the scope of protection of the present invention.

Claims

1. A multi-path anti-interference quantum key distribution system, characterized in that: The system comprises: A transmitting end and a receiving end, a control unit in communication with the receiving end and the transmitting end, wherein the transmitting end is connected to the receiving end via a reference path and m delayed paths; The transmitting end encodes the light pulse emitted in the current cycle based on the randomly selected phase coding, splits the phase-coded quantum state light pulse, and inputs it into the reference path and the randomly selected delay path of the current cycle respectively; the receiving end combines the quantum state light pulses output by the reference path and the delay path, detects the quantum state light pulse with enhanced interference, records the detection results of the current cycle and sends them to the control unit, which determines the optimal delay path under the current environment.

2. The multi-path anti-interference quantum key distribution system according to claim 1, characterized in that: The system also includes: A first optical switch and a second optical switch are provided at both ends of all delay paths, and the first optical switch and the second optical switch are communicatively connected with the control unit; The first optical switch is arranged at the transmitting end, and the beam splitter is connected to all delay paths through the first optical switch; the second optical switch is arranged at the receiving end, and the beam combiner is connected to all delay paths through the second optical switch; the control unit randomly selects a delay path based on the current cycle, and controls the first and second optical switches to switch to the randomly selected delay path.

3. The multi-path anti-interference quantum key distribution system according to claim 1, characterized in that: The transmission time of a quantum light pulse on the reference path is L, and the transmission time on the delayed path is L+n△L. The value of n for each delayed path is different.

4. The multi-path anti-interference quantum key distribution system according to claim 1, wherein: The transmitting end includes a laser, an intensity modulator, a phase modulator, and a beam splitter connected in sequence; The laser emits a laser pulse, the intensity of which is adjusted by an intensity modulator, and the phase of which is modulated by a phase modulator. The phase-encoded quantum state light pulse is input into a beam splitter, which splits the phase-encoded quantum state light pulse into two beams, which are input into a reference path and a randomly selected delay path respectively.

5. The multi-path anti-interference quantum key distribution system according to claim 1, characterized in that: The receiving end includes: Beam combiner and single photon detector SPD; the quantum state light pulses output from the reference path and the delay path are combined by the beam combiner and input into the single photon detector SPD, and the single photon detector SPD detects the interference-enhanced quantum state light pulses.

6. The multi-path anti-interference quantum key distribution system according to claim 1, characterized in that: The control unit records the number of responses of the single-photon detector SPD when quantum state light pulses are transmitted based on the reference path and the selected delay path in each cycle, and takes the delay path with the largest number of responses of the single-photon detector SPD in a unit cycle as the optimal delay path under the current environment.

7. The multi-path anti-interference quantum key distribution system according to claim 2, characterized in that: After determining the optimal delay path under the current environment, the first optical switch and the second optical switch are controlled to switch to the optimal delay path, and the optimal delay path and the reference path are used as the optical pulse transmission channel between the receiving end and the transmitting end under the current environment.

8. The multi-path anti-interference quantum key distribution system according to claim 4, characterized in that: The phase modulator supports 3 to 8 phase encodings in the range of 0 to π, and the phase differences between adjacent phases are equal.

9. The multi-path anti-interference quantum key distribution system according to claim 1, characterized in that: The value range of m is 3 to 8.

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