Quantum key receiving device, decoding method and quantum key distribution system

Abstract

The invention discloses a quantum key receiving device, which is used for carrying out random quantum state demodulation on a received first single photon in a clock period, carrying out interference and detection on the demodulated single photon in sequence, and responding to a detection signal detected for the first time in each clock period. Due to the fact that quantum light in the quantum key distribution system is influenced by loss of channels and optical systems, most of the quantum light generated by the quantum key sending device cannot be detected by the single-photon detector of the quantum key receiving device, and the single-photon detector has a period of dead time once detection output exists. According to the method, a frequency reduction decoding method is designed, decoding information is modulated in a speed reduction mode, control logic only responds to a detection signal once in the same period, the decoding driving complexity is greatly reduced, the random number demand quantity of the quantum key receiving device is greatly reduced, and the production cost is reduced.

Description

Technical Field

[0001] The present invention belongs to the field of quantum communication technology, and more specifically, the present invention relates to a quantum key receiving device and a decoding method thereof, and a quantum key distribution system. Background Art

[0002] As an emerging strategic commanding height in the future information and communication industry, quantum secure communication has become one of the main battlefields for national scientific and technological strength competition.

[0003] In the practical application of quantum secure communication technology, the quantum light trigger frequency of the quantum key distribution system determines the achievable key distribution rate. With the expansion of the communication network range and the improvement of bandwidth, people have higher requirements for the delay of data transmission and the rate of key generation. The current low-speed quantum key distribution system can no longer meet the growing demand for the industrial development of quantum secure communication. Therefore, the development of high-speed quantum key distribution system is becoming more and more important to the development of the entire industry.

[0004] In the process of high-speed research, existing technologies have improved the speed of the original system by improving the optical system, electronic system and software control system, and have built a 2GHz differential phase quantum key distribution system. However, as the system modulation rate increases, the system design, especially the decoding design, becomes increasingly difficult. Summary of the invention

[0005] The present invention provides a quantum key receiving device, aiming to improve the above-mentioned problem.

[0006] The present invention is implemented as follows: a quantum key receiving device, which randomly demodulates the first single photon received within a clock cycle, interferes and detects the demodulated photons in turn, and responds to the detection signal detected for the first time within each clock cycle.

[0007] Further, the decoding device includes: a first circulator, a first interferometer, a single photon detection unit, a first logic control module, and a decoding drive module;

[0008] A first circulator, used for receiving single photons generated by a transmitting end;

[0009] A first interferometer includes a decoder and an interference circuit, wherein the encoder performs random quantum state demodulation on single photons, and the interference circuit performs interference on the demodulated photons;

[0010] A decoding driving module, used for driving the first interferometer to perform random quantum state demodulation on a single photon;

[0011] A single photon detection unit, used to detect single photons received by the first circulator and / or photons interfered by the first interferometer, to obtain a detection signal;

[0012] The first control logic module is used to receive the detection signal, respond to the detection signal received for the first time in each clock cycle, and periodically drive the single photon detection unit and the decoding drive module, and the driving cycle is the same as the clock cycle.

[0013] Furthermore, the clock period is set to the detection time of the single photon detection unit.

[0014] Furthermore, the single-photon detection unit uses two single-photon detectors, one single-photon detector is connected to a port of the first circulator, and the other single-photon detector is connected to the output of the first interferometer.

[0015] Further, the first interferometer is any one of interferometer I, interferometer II or interferometer III;

[0016] Interferometer I includes: a 2×2 beam splitter, a first Faraday reflector, a phase modulator and a second Faraday reflector; the 2×2 beam splitter includes an input end and an output end located on the same side, and a first port and a second port located on the other side, and the input end and the output end are respectively the input end and the output end of the first interferometer or the second interferometer; the first port is connected to the first Faraday reflector, and the second port is connected to the phase modulator and the second Faraday reflector in sequence, and the phase modulator is an encoder or a decoder;

[0017] Interferometer II includes: a 1×2 beam splitter, a phase modulator and a 2×1 beam combiner; the 1×2 beam splitter includes an input end and two output ends, one output end of the 1×2 beam splitter is connected to an input end of the 2×1 beam combiner through a phase modulator, and the other output end of the 1×2 beam splitter is directly connected to the other input end of the 2×1 beam combiner.

[0018] Interferometer III includes: a 2×2 beam splitter, a 1×2 polarization beam splitter, a Faraday rotator and a phase modulator; the 2×2 beam splitter includes an input end and an output end located on the same side, and a first port and a second port located on the other side; and the input end and the output end are respectively the input end and the output end of the first interferometer or the second interferometer; the first port is connected to the Faraday reflector, the second port is connected to the 1×2 polarization beam splitter, the Faraday rotator and the phase modulator in sequence, and the 1×2 polarization beam splitter, the Faraday rotator and the phase modulator are connected end to end.

[0019] The present invention is implemented in this way. The quantum key decoding method based on the above-mentioned quantum key receiving device includes:

[0020] (1) Quantum light enters the first circulator from the quantum channel;

[0021] (2) The quantum light enters the first interferometer from the first circulator, and the decoder periodically demodulates the quantum light in a random quantum state, and then completes the interference of the quantum light in the interference optical path;

[0022] (3) The single-photon detection unit detects the photons after interference to generate a detection signal and sends it to the first control logic;

[0023] (4) The first control logic responds to the detection signal received for the first time within the clock cycle.

[0024] The present invention is implemented as follows: a quantum key distribution system, the quantum key distribution system comprising:

[0025] A quantum key sending device and a quantum key receiving device, wherein the quantum key sending device and the quantum key receiving device are connected via a quantum channel;

[0026] The quantum key sending device generates quantum light, modulates and attenuates the quantum light in a random quantum state to obtain a single photon, and then sends the single photon to the quantum key receiving device through a quantum channel.

[0027] Furthermore, the quantum key sending device includes:

[0028] A quantum light preparation module, a second interferometer, a coding drive module, an optical attenuator, a second circulator and a second control logic module;

[0029] Quantum light preparation module, used to prepare quantum light;

[0030] A second interferometer includes an encoder and an interference circuit, the encoder performs random quantum state modulation on the quantum light, and the interference circuit interferes with the modulated quantum light;

[0031] An encoding driving module, used to drive the encoder to perform random quantum state modulation on quantum light;

[0032] An optical attenuator, used to attenuate the quantum light after interference into single photons;

[0033] a second circulator, for sending the single photon to a transmitting end;

[0034] The second control logic module is used to periodically drive the quantum light preparation module, the encoding drive module and the optical attenuator.

[0035] Further, the optical attenuator includes at least one of a fixed optical attenuator and an electrically controlled optical attenuator.

[0036] The quantum key receiving device proposed in the present invention has the following beneficial effects:

[0037] (1) Since the quantum light in the quantum key distribution system is affected by the loss of the channel and the optical system, most of the quantum light generated by the quantum key sending device will not be detected by the single-photon detector of the quantum key receiving device, and once the single-photon detector has a detection output, there will be a period of dead time. Based on the above characteristics, the present invention designs a method of down-conversion decoding, down-modulates the decoding information, and controls the logic to respond to the detection signal only once in the same cycle. This method not only greatly reduces the complexity of decoding drive, but also greatly reduces the random number demand of the quantum key receiving device, thereby reducing the production cost;

[0038] (2) The quantum state decoding modulation rate of the quantum key receiving device provided by the present invention does not need to be increased as the quantum state modulation frequency is increased, which simplifies the difficulty of electronic control. It is not only beneficial to improve the modulation rate of the quantum key distribution system, but also beneficial to reduce the equipment cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A schematic diagram of the structure of a key receiving device provided in an embodiment of the present invention;

[0040] Figure 2 A flowchart of a quantum key decoding method for a key receiving device provided in an embodiment of the present invention;

[0041] Figure 3 A schematic diagram of the structure of a quantum key sending device provided by an embodiment of the present invention;

[0042] Figure 4 A flowchart of a quantum key encoding method for a quantum key sending device provided in an embodiment of the present invention;

[0043] Figure 5 A schematic diagram of the structure of an interferometer I provided in an embodiment of the present invention;

[0044] Figure 6 A schematic diagram of the structure of an interferometer II provided in an embodiment of the present invention;

[0045] Figure 7 A schematic diagram of the structure of the interferometer III provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0046] The specific implementation modes of the present invention are 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.

[0047] The quantum key distribution system includes: a quantum key sending device and a quantum key receiving device, and quantum communication is performed between the quantum key sending device and the quantum key receiving device via a quantum channel;

[0048] The quantum key sending device prepares quantum light, performs random quantum state modulation on the quantum light, decays the modulated quantum light into single photons, and sends the single photons to the receiving end through the quantum channel;

[0049] In one clock cycle, the key receiving device performs random quantum state demodulation on the first single photon received, interferes with and detects the demodulated photons, and responds to the detection signal detected for the first time in each clock cycle.

[0050] The present invention loads the down-converted decoding information into the decoder through the decoding driver. When a detection signal is output, the control logic module will only respond to the first detection signal received in the same cycle and will no longer respond to other detection signals.

[0051] Figure 1 The schematic diagram of the structure of the key receiving device provided in the embodiment of the present invention, for the convenience of explanation, only shows the part related to the embodiment of the present invention, the key receiving device includes:

[0052] A first circulator, a first interferometer, a single photon detection unit, a first logic control module, and a decoding drive module;

[0053] A first circulator, used for receiving single photons generated by a transmitting end;

[0054] A first interferometer includes a decoder and an interference circuit, wherein the encoder performs random quantum state demodulation on single photons, and the interference circuit performs interference on the demodulated photons;

[0055] A decoding driving module, used for driving the first interferometer to perform random quantum state demodulation on a single photon;

[0056] A single photon detection unit, used to detect single photons received by the first circulator and / or photons interfered by the first interferometer, to obtain a detection signal;

[0057] The first control logic module is used to receive the detection signal, respond to the detection signal received for the first time in each clock cycle, and periodically drive the single-photon detection unit and the decoding drive module. The driving period is the same as the clock period. In an embodiment of the present invention, the clock period is set to the detection time of the single-photon detection unit.

[0058] The number of single-photon detectors used in the photon detection unit is one or two. In practice, in order to save costs, one single-photon detector is used to realize photon detection with a phase difference (0 or π). Of course, two single-photon detectors can also be set up. One single-photon detector is directly connected to a port of the first circulator (including three ports, which are respectively connected to the quantum channel, the first interferometer and the single-photon detector), and the other single-photon detector is connected to the output of the first interferometer. The photons detected by the two single-photon detectors are all photons after interference by the first interferometer. One single-photon detector is used for photon detection with a phase difference of 0 (the phase of the incident photon is the same as the phase of the outgoing photon), and the other is used for photon detection with a phase difference of π.

[0059] Figure 2 A flowchart of a quantum key decoding method for a key receiving device provided in an embodiment of the present invention, the method comprising the following steps:

[0060] (1) Quantum light enters the first circulator from the quantum channel, which mainly prevents Trojan horse attacks at the receiving end;

[0061] (2) The quantum light enters the first interferometer from the first circulator, and the decoder periodically demodulates the quantum light in a random quantum state, and then completes the interference of the quantum light in the interference optical path;

[0062] The signal light can be randomly demodulated into two phases, namely 0 and π / 2, or randomly demodulated into four phases, namely 0, π / 2, π, and 3π / 2.

[0063] (3) The single-photon detection unit detects the photons after interference to generate a detection signal and sends it to the first control logic;

[0064] (4) The first control logic module responds to the first detection signal received within the clock cycle and shields the subsequent detection signals.

[0065] Figure 3 The schematic diagram of the structure of the quantum key sending device provided in the embodiment of the present invention, for the convenience of explanation, only shows the part related to the implementation of the present invention, the quantum key sending device includes:

[0066] A quantum light preparation module, a second interferometer, a coding drive module, an optical attenuator, a second circulator and a second control logic module;

[0067] Quantum light preparation module, used to prepare quantum light;

[0068] A second interferometer includes an encoder and an interference circuit, the encoder performs random quantum state modulation on the quantum light, and the interference circuit interferes with the modulated quantum light;

[0069] An encoding driving module, used to drive the encoder to perform random quantum state modulation on quantum light;

[0070] An optical attenuator, used to attenuate the quantum light after interference into single photons;

[0071] a second circulator, for sending the single photon to a transmitting end;

[0072] The second control logic module is used to periodically drive the quantum light preparation module, the encoding drive module and the optical attenuator.

[0073] In an embodiment of the present invention, the optical attenuator includes at least one of a fixed optical attenuator and an electrically controlled optical attenuator. If the attenuation of an optical attenuator can attenuate the quantum light to the single photon level, only one optical attenuator can be used. If one optical attenuator cannot attenuate the quantum light to the single photon level, the quantum light is allowed to pass through two optical attenuators to attenuate the optical pulse to the single photon level.

[0074] Figure 4 A flowchart of a quantum key encoding method for a quantum key sending device provided in an embodiment of the present invention, the method comprising:

[0075] (1) Using a clock signal to trigger the laser to emit quantum light;

[0076] The signal light is generally a narrow pulse of the laser in the gain switching mode. In the decoy state modulation scheme, the signal light emitted by the laser is also subjected to random intensity modulation by an intensity modulator to become quantum light of the signal state and the decoy state. The number of decoy states can be one or more, and the light intensities of the multiple decoy states can be consistent or inconsistent.

[0077] (2) The emitted quantum light enters the second interferometer, the encoder performs random quantum state modulation on the quantum light, and the interference optical path is used to interfere with the modulated quantum light;

[0078] Quantum light can be randomly modulated into four phases: 0, π / 2, π, and 3π / 2.

[0079] (3) The quantum light after interference is attenuated into single photons by an optical attenuator;

[0080] (4) The single light enters the quantum channel after passing through the second circulator, whose main function is to prevent Trojan horse attacks at the transmitting end.

[0081] There is a first interferometer in the quantum key sending device, and there is a second interferometer in the quantum key receiving device. The first interferometer and the second interferometer can be implemented by the following three interferometer structures. The first interferometer and the second interferometer can adopt one of the same interferometer structures, and of course, different interferometer structures can also be adopted. The three interferometer structures are as follows:

[0082] (1) The schematic diagram of the structure of interferometer I is as follows Figure 5 As shown, interferometer I includes: a 2×2 beam splitter (50:50 beam splitter), a first Faraday reflector, a phase modulator and a second Faraday reflector;

[0083] The 2×2 optical splitter includes an input end and an output end located on the same side, and a first port and a second port located on the other side, and the input end and the output end are respectively the input end and the output end of the first interferometer or the second interferometer; the first port is connected to the first Faraday reflector, and the second port is connected to the phase modulator and the second Faraday reflector in sequence, and the phase modulator is the encoder or the decoder;

[0084] The two ends on the same side of the 2×2 beam splitter serve as the input and output ends of the first interferometer respectively. The two ends on the other side of the 2×2 beam splitter are each connected to a Faraday reflector to form two interference arms, and the phase modulator is connected to one of the two interference arms. It should be noted that the phase modulator can be a waveguide phase modulator, a piezoelectric ceramic phase modulator, etc. When it is implemented, the light pulse entering the interferometer I is first divided into two wave packets with equal polarization through the 2×2 beam splitter, and enters the long arm and short arm of the unequal arm interferometer respectively. Since the time interval between the two wave packets with the same polarization is very short, it can be regarded as the same polarization state change in the channel. If the same structure is used at the receiving end, it can be ensured that the polarization state of the two light pulse wave packets for interference is always the same. Therefore, no matter how the polarization state changes in the channel, the interferometer can adaptively compensate, thereby ensuring the polarization robustness of the quantum key distribution system.

[0085] (2) The structure of interferometer II is as follows Figure 6 As shown, interferometer II includes: a 1×2 beam splitter (50:50 beam splitter), a phase modulator and a 2×1 beam combiner (50:50 beam splitter);

[0086] The 1×2 optical splitter includes an input end and two output ends. One output end of the 1×2 optical splitter is connected to an input end of the 2×1 optical combiner through a phase modulator, and the other output end of the 1×2 optical splitter is directly connected to the other input end of the 2×1 optical combiner.

[0087] It should be noted that the phase modulator in interferometer II can be a waveguide phase modulator, a piezoelectric ceramic phase modulator, etc. When it is working, the light pulse enters the 1×2 beam splitter and is divided into two light pulses, which pass through the arm containing the phase modulator and the arm without the phase modulator respectively, and finally interfere at the 2×1 light combiner and output from the port on the right side of the 2×1 light combiner.

[0088] (3) The structure of interferometer III is as follows Figure 7As shown, interferometer III includes: 2×2 beam splitter, 1×2 polarization beam splitter, Faraday rotator mirror and phase modulator;

[0089] A 2×2 beam splitter comprises an input end and an output end located on the same side, and a first port and a second port located on the other side; and the input end and the output end are respectively the input end and the output end of the first interferometer or the second interferometer; the first port is connected to a Faraday reflector, and the second port is connected to a 1×2 polarization beam splitter, a Faraday rotator and a phase modulator in sequence, and the 1×2 polarization beam splitter, the Faraday rotator and the phase modulator are connected end to end.

[0090] It should be noted that the phase modulator in interferometer III can be a waveguide phase modulator, a piezoelectric ceramic phase modulator, etc. The two ends on the same side of the 2×2 beam splitter serve as the input and output ends of interferometer III respectively. The two ends on the other side of the 2×2 beam splitter, one end of which is connected to a Faraday reflector to form an interference arm, and the other interference arm is composed of a 1×2 polarization beam splitter, a Faraday rotator and a phase modulator connected end to end. The light pulse entering interferometer III first passes through the 2×2 beam splitter to be divided into two wave packets with equal polarization, and enters the long arm and short arm of the unequal arm interferometer respectively. Since the time interval between the two wave packets with the same polarization is very short, they can be regarded as having the same polarization state change in the channel. If the same structure is used at the receiving end, it can be guaranteed that the polarization state of the two light pulse wave packets that interfere are always the same. Therefore, interferometer III inherits the stability of the existing technology in terms of optical polarization characteristics. At the same time, the two parts of the light pulse in the long arm pass through the phase modulator at the same time, which reduces the round-trip time between the phase modulator and the Faraday reflector in the long arm of interferometer I, and can support a higher encoding and decoding rate; moreover, both parts of the light pulse pass through the phase modulator once, which is equivalent to the entire light pulse passing through the phase modulator only once, and the insertion loss is also better than that of interferometer I.

[0091] 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 protection scope of the present invention.

Claims

1. A quantum key receiving device, characterized in that: The quantum key receiving device performs random quantum state demodulation on the first received single photon within a clock cycle, interferes and detects the demodulated quantum photons in sequence, and responds to the detection signal detected for the first time within each clock cycle.

2. The quantum key receiving device according to claim 1, characterized in that: The decoding device comprises: a first circulator, a first interferometer, a single photon detection unit, a first logic control module, and a decoding drive module; A first circulator, for receiving a single photon generated by a transmitting end; A first interferometer includes a decoder and an interference circuit, wherein the encoder performs random quantum state demodulation on single photons, and the interference circuit performs interference on the demodulated photons; A decoding driving module, used for driving the first interferometer to perform random quantum state demodulation on a single photon; A single photon detection unit, used to detect single photons received by the first circulator and / or photons interfered by the first interferometer, to obtain a detection signal; The first control logic module is used to receive the detection signal, respond to the detection signal received for the first time in each clock cycle, and periodically drive the single photon detection unit and the decoding drive module, and the driving cycle is the same as the clock cycle.

3. The quantum key receiving device according to claim 2, characterized in that: The clock period is set as the detection time of the single photon detection unit.

4. The quantum key receiving device according to claim 2, characterized in that: The single-photon detection unit adopts two single-photon detectors, one of which is connected to a port of the first circulator, and the other is connected to the output of the first interferometer.

5. The quantum key receiving device according to claim 2, characterized in that: The first interferometer is any one of interferometer I, interferometer II or interferometer III; Interferometer I includes: a 2×2 beam splitter, a first Faraday reflector, a phase modulator and a second Faraday reflector; the 2×2 beam splitter includes an input end and an output end located on the same side, and a first port and a second port located on the other side, and the input end and the output end are respectively the input end and the output end of the first interferometer or the second interferometer; the first port is connected to the first Faraday reflector, and the second port is connected to the phase modulator and the second Faraday reflector in sequence, and the phase modulator is an encoder or a decoder; Interferometer II includes: a 1×2 beam splitter, a phase modulator and a 2×1 beam combiner; the 1×2 beam splitter includes an input end and two output ends, one output end of the 1×2 beam splitter is connected to an input end of the 2×1 beam combiner through a phase modulator, and the other output end of the 1×2 beam splitter is directly connected to the other input end of the 2×1 beam combiner. Interferometer III includes: a 2×2 beam splitter, a 1×2 polarization beam splitter, a Faraday rotator and a phase modulator; the 2×2 beam splitter includes an input end and an output end located on the same side, and a first port and a second port located on the other side; and the input end and the output end are respectively the input end and the output end of the first interferometer or the second interferometer; the first port is connected to the Faraday reflector, the second port is connected to the 1×2 polarization beam splitter, the Faraday rotator and the phase modulator in sequence, and the 1×2 polarization beam splitter, the Faraday rotator and the phase modulator are connected end to end.

6. A quantum key decoding method based on the quantum key receiving device according to any one of claims 1 to 5, characterized in that: The method comprises: (1) Quantum light enters the first circulator from the quantum channel; (2) The quantum light enters the first interferometer from the first circulator, and the decoder periodically demodulates the quantum light in a random quantum state, and then completes the interference of the quantum light in the interference optical path; (3) The single-photon detection unit detects the photons after interference to generate a detection signal and sends it to the first control logic; (4) The first control logic responds to the detection signal received for the first time within the clock cycle.

7. A quantum key distribution system, characterized in that: The quantum key distribution system comprises: A quantum key sending device and a quantum key receiving device, wherein the quantum key sending device and the quantum key receiving device are connected via a quantum channel; The quantum key sending device generates quantum light, performs random quantum state modulation on the quantum light, obtains single photons after attenuation, and sends the single photons to the quantum key receiving device as described in any one of claims 1 to 5 through a quantum channel.

8. The quantum key distribution system according to claim 7, characterized in that: The quantum key sending device includes: A quantum light preparation module, a second interferometer, a coding drive module, an optical attenuator, a second circulator and a second control logic module; Quantum light preparation module, used to prepare quantum light; A second interferometer includes an encoder and an interference circuit, the encoder performs random quantum state modulation on the quantum light, and the interference circuit interferes with the modulated quantum light; An encoding driving module, used to drive the encoder to perform random quantum state modulation on quantum light; An optical attenuator, used to attenuate the quantum light after interference into single photons; a second circulator, for sending the single photon to a transmitting end; The second control logic module is used to periodically drive the quantum light preparation module, the encoding drive module and the optical attenuator.

9. The quantum key distribution system according to claim 8, characterized in that: The optical attenuator includes at least one of a fixed optical attenuator and an electrically controlled optical attenuator.

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