Free-space continuous-variable quantum key distribution method and system based on thermal state source

Abstract

The application provides a kind of free space continuous variable quantum key distribution method and system based on thermal state source, it is related to quantum key distribution technical field, including: continuous variable initial key distribution step: the detection result of regular component X and P after sending party Alice utilizes thermal state source polarization beam splitting, as local initial key;And another half thermal state optical signal is attenuated after transmission after being combined with local light through free space channel, by receiving party Bob detection, obtain corresponding initial continuous key data;Continuous data post-processing step: Bob carries out bit frame synchronization, block phase compensation, parameter evaluation, error correction and security enhancement to the initial continuous key data obtained, finally obtains safe binary bit key.The application can reduce the complexity of continuous variable quantum key distribution system implementation, and provide new application scenarios for quantum key distribution system.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of quantum key distribution, in particular to a free space channel continuous variable quantum key distribution (CVQKD) method based on a thermal state source, and more particularly to a free space continuous variable quantum key distribution method and system based on a thermal state source. BACKGROUND

[0002] At present, most of the continuous variable quantum key distribution systems (CVQKD) are implemented by using amplitude and phase modulators to modulate and encode random key information generated by quantum random number into weak coherent light, such as Gaussian modulation, that is, using amplitude and phase modulators to modulate Gaussian distributed quantum random number to the canonical component of weak coherent light, and sending it to the receiving party through an optical fiber or a free space channel. Similarly, the discrete modulation CVQKD system is realized by using amplitude and phase modulators to modulate a limited number of quantum states, and sending them to the receiving party for demodulation and detection.

[0003] These two methods need to use quantum random number generators and use active amplitude and phase modulators to realize linear modulation of optical signals. On the other hand, the actual devices and operating states often have nonlinear effects, which cause the initial key information generated to be unable to be linearly modulated on the optical field component, resulting in complex system implementation.

[0004] In addition, in the field of quantum key distribution of thermal state light sources, the current progress is still based on the transmission of local oscillator light and signal light in separate short distance optical fibers. There is no relatively inexpensive quantum key distribution scheme that can be applied in a free space channel. SUMMARY

[0005] In view of the defects in the prior art, the present application provides a free space continuous variable quantum key distribution method and system based on a thermal state source.

[0006] According to the free space continuous variable quantum key distribution method and system based on a thermal state source provided by the present application, the scheme is as follows:

[0007] In a first aspect, a free space continuous variable quantum key distribution method based on a thermal state source is provided, and the method comprises:

[0008] A continuous variable initial key distribution step: the detection results of the canonical components X and P of the thermal state source after being polarized and split by the sender Alice are used as local initial keys; and the other half of the thermal light signal is attenuated, combined with the local oscillator light, transmitted through a free space channel, and detected by the receiving party Bob to obtain corresponding initial continuous key data;

[0009] Continuous data post-processing step: Bob performs bit frame synchronization, block phase compensation, parameter evaluation, error correction and security enhancement on the obtained initial continuous key data, and finally obtains a secure binary bit key.

[0010] Preferably, the continuous variable initial key distribution step comprises:

[0011] Step S1.1: The sender Alice and the receiver Bob initialize the communication of the continuous variable quantum key distribution system based on the thermal light source, including the initialization of the ASE thermal source, the coherent light source, the optical amplifier, the optical band-pass filter, the polarization beam splitter, the 90° optical hybrid, the quantum balanced homodyne detector and the control circuit in the system.

[0012] Step S1.2: Alice amplifies the ASE thermal source through the optical amplifier, passes it through the narrow-band optical filter, and divides it into two paths through the 50:50 optical beam splitter. One path is combined with the local oscillator signal of the coherent light source through the 50:50 optical beam splitter after passing through the optical attenuator, and is sent to the receiver Bob through the free space channel as the local oscillator light beam. The other path is kept locally and input into the optical hybrid with the other half of the coherent light signal for quantum balanced homodyne detection, and the thermal regular components X and P are obtained as the initial key data K1.

[0013] Step S1.3: Bob demultiplexes the polarization multiplexed signal sent by Alice into local oscillator signals and thermal signals, respectively, and inputs them into the quantum balanced homodyne detector through the polarization control optical hybrid to obtain the received thermal regular components X and P as the initial key data K2.

[0014] Preferably, the step S1.2 comprises:

[0015] Step S1.2.1: Alice adjusts the ASE thermal source, optical amplifier and optical attenuator to control the average photon number, so that the average photon number of the thermal light signal passing through the 50:50 optical beam splitter and attenuator satisfies n=0.5mn0.

[0016] Where m is the attenuation factor of the optical attenuator, n0 is the average photon number of the thermal light signal after the band-pass filter, and the thermal regular component obeys a Gaussian distribution with a mean of zero and a variance of V A =mn0; where V A is greater than 0 and less than 80, and is sent to Bob through the free space channel.

[0017] Step S1.2.2: Alice retains the other half of the hot light signal split by the 50:50 optical beam splitter locally, and inputs the part of the light signal split by the 50:50 optical beam splitter generated by Alice simultaneously with the continuous coherent light signal into the Hybrid optical mixer, realizes the interference of the two continuous light signals, and obtains the initial key data X through the quantum balanced homodyne detector, and the other part is sent to Bob together with the signal light through polarization beam combining.

[0018] Preferably, the continuous data post-processing step comprises:

[0019] Step S2.1: Bob and Alice perform multi-round bit frame synchronization of the initial continuous key data without special modulation frames, and perform phase compensation based on data processing.

[0020] Step S1.2: Alice and Bob publish part of the initial key data for parameter evaluation, and obtain signal noise, modulation variance, and channel transmittance parameters.

[0021] Step S1.3: Bob performs error correction on the initial continuous key data after phase compensation through an efficient multi-dimensional negotiation algorithm based on LDPC encoding, and outputs consistent binary shared key strings.

[0022] Step S1.4: Bob calculates the Holevo limit and the mutual information of the legitimate communication party through the channel parameters, obtains the information compression rate, and finally outputs the final key through security enhancement.

[0023] Preferably, an isolator, a light detector PD, and an optical power meter are arranged in the optical path of Alice and Bob to monitor the light intensity of the hot light source and the local oscillator light.

[0024] In a second aspect, a free space continuous variable quantum key distribution system based on a hot state source is provided, and the system comprises:

[0025] A continuous variable initial key distribution module: the detection results of the regular components X and P split by the hot state source by the sender Alice are used as the local initial key; and the other half of the hot light signal is attenuated and transmitted through the free space channel after being combined with the local oscillator light, and is detected by the receiver Bob to obtain the corresponding initial continuous key data.

[0026] A continuous data post-processing module: Bob performs bit frame synchronization, block phase compensation, parameter evaluation, error correction, and security enhancement on the obtained initial continuous key data, and finally obtains a secure binary bit key.

[0027] Preferably, the continuous variable initial key distribution module comprises:

[0028] Module M1.1: the sender Alice and the receiver Bob initialize the communication of the continuous variable quantum key distribution system based on the thermal light source, including the initialization of the ASE thermal source, the coherent light source, the optical amplifier, the optical band-pass filter, the polarization beam splitter, the 90° optical hybrid, the quantum balanced homodyne detector and the control circuit in the system;

[0029] Module M1.2: the Alice end amplifies the ASE thermal source through the optical amplifier, passes the narrow-band optical filter, and divides the thermal light signal into two paths through the 50:50 optical beam splitter. One path is combined with the local oscillator light signal through the 50:50 optical beam splitter after passing through the optical attenuator, and is sent to the receiver Bob through the free-space channel as the local oscillator light. The other path is input into the optical hybrid together with the other half of the coherent light signal for quantum balanced homodyne detection, and the thermal regular components X and P are obtained as the initial key data K1.

[0030] Module M1.3: Bob demultiplexes the polarization multiplexed signal received from Alice into the local oscillator signal and the thermal signal, respectively inputs them into the polarization control optical hybrid for quantum balanced homodyne detection, and obtains the received thermal regular components X and P as the initial key data K2.

[0031] Preferably, the module M1.2 includes:

[0032] Module M1.2.1: Alice adjusts the ASE thermal source, the optical amplifier and the optical attenuator to control the average photon number, so that the average photon number of the thermal light signal passing through the 50:50 optical beam splitter and the attenuator satisfies n=0.5mn0.

[0033] Wherein, m is the attenuation factor of the optical attenuator, n0 is the average photon number of the thermal light signal after the band-pass filter, and the thermal regular component obeys the Gaussian distribution with mean zero and variance V A =mn0; wherein, V A is greater than 0 and less than 80, and is sent to Bob through the free-space channel.

[0034] Module M1.2.2: Alice retains the other half of the thermal light signal split by the 50:50 optical beam splitter, and inputs it into the Hybrid optical hybrid together with the continuous coherent light signal generated by Alice at the same time, so as to realize the interference of the two continuous light signals, and obtain the initial key data X through the quantum balanced homodyne detector. The other path is sent to Bob together with the signal light through polarization beam combining.

[0035] Preferably, the continuous data post-processing module includes:

[0036] Module M2.1: Bob and Alice perform multi-round bit frame synchronization of the initial continuous key data without special modulation frame, and perform phase compensation based on data processing;

[0037] Module M1.2: Alice and Bob publish part of the initial key data for parameter evaluation, and obtain signal over noise, modulation variance and channel transmittance parameters;

[0038] Module M1.3: Bob performs error correction on the initial continuous key data after phase compensation through an efficient multi-dimensional negotiation algorithm based on LDPC coding, and outputs consistent binary shared key string;

[0039] Module M1.4: Bob calculates Holevo limit and mutual information of the legal communication party through channel parameters, obtains information compression rate, and finally outputs the final key through security enhancement.

[0040] Preferably, isolators and optical detectors PD and optical power meters are arranged in the optical paths of Alice and Bob to monitor the light intensity of the hot light source and the local oscillator light.

[0041] Compared with the prior art, the present application has the following beneficial effects:

[0042] 1. The present application can realize CVQKD security coding based on a hot light source in a free space channel, which is the first method to realize security coding in a free space channel based on a hot light source internationally.

[0043] 2. The polarization multiplexing of the present application in the polarization light beam combining and splitting in the continuous variable initial key distribution step realizes the polarization multiplexing of the hot light source scheme, so that the signal light and the local oscillator light can be stably transmitted in the free space along with the channel characteristics.

[0044] 3. The multi-round block bit frame synchronization algorithm and the phase compensation algorithm in the continuous data post-processing step of the present application can adjust the size of the communication data block, and the phase compensation algorithm can greatly reduce the additional over noise introduced by the large data block caused by phase jitter. It can ensure the security coding in the free space within the indoor range. BRIEF DESCRIPTION OF DRAWINGS

[0045] Other features, objects and advantages of the present application will become more apparent from the following detailed description of non-limiting embodiments, made with reference to the accompanying drawings:

[0046] Figure 1 It is a schematic diagram of the continuous variable quantum key distribution method based on a hot light source. DETAILED DESCRIPTION

[0047] The application will be described in detail below with specific embodiments. The following examples will help those skilled in the art to further understand the application, but do not limit the application in any form. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the application. These are within the scope of protection of the application.

[0048] The embodiment of the application provides a free space continuous variable quantum key distribution method based on a thermal state source. Figure 1 As shown in the figure, the specific steps are as follows:

[0049] The continuous variable initial key distribution step: the detection results of the regular components X and P of the thermal state source after polarization beam splitting by the sender Alice are used as the local initial key; and the other half of the thermal state optical signal is attenuated, combined with the local oscillator light after transmission through the free space channel, and detected by the receiver Bob to obtain the corresponding initial continuous key data. Isolators, optical detectors PD and optical power meters are arranged in the optical paths of Alice and Bob to monitor the thermal light source and the intensity of the local oscillator light.

[0050] Specifically, the continuous variable initial key distribution step includes:

[0051] Step S1.1: The sender Alice and the receiver Bob initialize the continuous variable quantum key distribution (CVQKD) system based on the thermal light source, including initializing the ASE (amplified spontaneous emission) thermal source, the coherent light source, the optical amplifier, the optical bandpass filter, the polarization beam splitter, the 90° optical hybrid (Hybrid), the quantum balanced homodyne detector and the control circuit in the system.

[0052] Step S1.2: The Alice end amplifies the ASE thermal source through the optical amplifier, passes through the narrowband optical filter, and is divided into two paths through the 50:50 optical beam splitter. One path is combined with the local oscillator signal of the coherent light source through the 50:50 optical beam splitter as the receiving end local oscillator light beam through the free space channel to send to the receiver Bob, and the other path is left in the local oscillator, and the other half of the coherent light signal is input into the optical hybrid at the same time for quantum balanced homodyne detection, and the regular components X and P of the thermal state are obtained as the initial key data K1.

[0053] In this step S1.2, specifically includes:

[0054] Step S1.2.1: Alice adjusts the ASE thermal source, the optical amplifier and the optical attenuator to control the average photon number, so that the average photon number of the thermal light signal through the 50:50 optical beam splitter and the attenuator satisfies n=0.5mn0;

[0055] wherein m is the attenuation factor of the optical attenuator, n0 is the average photon number of the thermal light signal after the band-pass filter, and the thermal canonical component is subject to a Gaussian distribution with mean zero and variance V A = mn0; wherein V A is greater than 0 and less than 80, and is sent to Bob through a free space channel.

[0056] Step S1.2.2: Alice retains the other half of the thermal light signal split by the 50:50 optical beam splitter locally, and inputs the part of the optical signal split by the 50:50 optical beam splitter together with the continuous coherent light signal generated by Alice into the Hybrid optical mixer, realizes the interference of the two continuous light signals, and obtains the initial key data X (the values of the thermal canonical component X and P of the thermal light signal) through the quantum balanced homodyne detector, and the other part is sent to Bob together with the signal light through polarization beam combining.

[0057] Step S1.3: Bob demultiplexes the polarization multiplexed signal received from Alice into a local oscillator signal and a thermal signal, respectively inputs them into the optical mixer through polarization control for quantum balanced homodyne detection, and obtains the received thermal canonical component X and P as the initial key data K2.

[0058] Since the polarization multiplexing on-the-fly scheme is used, there is no need for time division, wavelength division multiplexing, and no need for pulse modulation, and Alice and Bob can realize the interference of continuous thermal signals and continuous coherent light signals, and use high-bandwidth quantum balanced heterodyne detection and high-bandwidth data acquisition cards to obtain the initial key data at high speed, thereby realizing high-code-rate continuous-variable quantum key distribution while reducing the requirements of the communication channel and expanding the application range of the scheme.

[0059] Continuous data post-processing step: Bob performs bit frame synchronization, block phase compensation, parameter evaluation, error correction and security enhancement on the obtained initial continuous key data, and finally obtains a secure binary bit key.

[0060] Specifically, the continuous data post-processing step includes:

[0061] Step S2.1: Bob and Alice perform multi-round bit frame synchronization of the initial continuous key data without special modulation frames, and perform phase compensation based on data processing.

[0062] Step S1.2: Alice and Bob publish part of the initial key data for parameter evaluation to obtain signal noise, modulation variance and channel transmittance parameters.

[0063] Step S1.3: Bob corrects errors of the initial continuous key data after phase compensation through a high-efficiency multi-dimensional negotiation algorithm based on LDPC coding, and outputs a consistent binary shared key string.

[0064] Step S1.4: Bob calculates Holevo limit and mutual information of legal communication parties through channel parameters, obtains information compression rate, and finally outputs a final key through security enhancement.

[0065] Next, the application will be described in more detail.

[0066] The embodiment of the application provides a free space continuous variable quantum key distribution method based on a thermal state source, as shown in the figure: Figure 1 The ASE (amplified spontaneous emission) is a thermal state source of amplified spontaneous emission, the 90° Hybrid is an optical hybrid, which includes two 50:50 beam splitters, which respectively divide the input two optical signals into two paths, wherein one of the signal beam splitting outputs is phase-rotated by 90°, and the other beam splitting output does not change the phase, and the Hom is a quantum balanced homodyne detector.

[0067] The continuous variable initial key distribution step is specifically:

[0068] 1): Alice divides the output of the thermal light source into two spatial modes mod1 and mod2 using a 50:50 optical fiber beam splitter.

[0069] 2): The spatial mode mod1 is heterodyne detected to simultaneously measure X canonical components and P canonical components to obtain corresponding initial continuous key data, and the other half of the thermal state light signal is attenuated and combined with the local coherent light by using polarization multiplexing through a polarization beam splitter.

[0070] 3): From the perspective of an eavesdropper, the quantum state transmitted by us is a mixture of all possible coherent states, which is only a thermal state with an average number of photons. It is security equivalent to Gaussian modulated continuous variable quantum key distribution. Due to the advantage of not needing modulation, we have the ability to realize free space quantum key distribution with low cost and light weight, and the advantage of high theoretical key generation rate. Our generation rate can linearly increase with the bandwidth of the detector without being limited by the overhead caused by coding.

[0071] The continuous data post-processing step is specifically: Bob performs bit frame synchronization, block phase compensation, parameter evaluation, error correction and security enhancement on the obtained initial continuous key data, and finally obtains a secure binary bit key. Specifically, the continuous variable initial key distribution step includes the following steps:

[0072] 1): The sender Alice and the receiver Bob initialize the communication of the continuous variable quantum key distribution (CVQKD) system based on the thermal light source, including the initialization of the ASE (amplified spontaneous emission) thermal source, the coherent light source, the optical amplifier, the optical band-pass filter, the polarization beam splitter, the 90° optical hybrid, the quantum balanced homodyne detector and the control circuit in the system;

[0073] 2): The Alice end amplifies the ASE thermal source through the optical amplifier, passes it through the narrow-band optical filter, and divides it into two paths through the 50:50 optical beam splitter. One path is combined with the local oscillator signal of the coherent light source through the 50:50 optical beam splitter after passing through the optical attenuator, and is sent to the receiver Bob through the free-space channel as the local oscillator light beam. The other path is left in the local, and the other half of the coherent light signal is input into the optical hybrid at the same time to perform quantum balanced homodyne detection, and the thermal regular components X and P are obtained as the initial key data K1.

[0074] The step 2) includes the following steps:

[0075] Alice adjusts the ASE light source, optical amplifier and optical attenuator to control the average photon number, so that the average photon number of the thermal light signal passing through the 50:50 optical beam splitter and the attenuator satisfies n = 0.5mn0; wherein m is the attenuation factor of the optical attenuator, n0 is the average photon number of the thermal light signal after passing through the band-pass filter, and the thermal regular component obeys the Gaussian distribution with a mean of zero and a variance of V A = mn0.

[0076] The value of V A is greater than 0 and less than 80, and is sent to Bob through a single-mode optical fiber channel.

[0077] Alice retains the other half of the thermal light signal split by the 50:50 optical beam splitter locally, and simultaneously inputs the part of the optical signal split by the 50:50 optical beam splitter after controlling the light intensity of the continuous coherent light signal generated by Alice through the optical attenuator into the Hybrid mixer, realizes the interference of the two continuous optical signals, and obtains the initial key data X (the values of the thermal regular components X and P of the light signal) through the quantum balanced homodyne detector, and the other optical fiber is sent to Bob.

[0078] Isolators and optical detectors PD are arranged in the optical paths of Alice and Bob to monitor the light intensity of the thermal light source and the local oscillator light.

[0079] 3) Bob demultiplexes the polarization multiplexed signal received from Alice into the local oscillator signal and the thermal state signal, and inputs them into the polarization control light mixer for quantum balanced homodyne detection to obtain the received thermal state canonical components X and P as the initial key data K2. Preferably, since two optical fibers are used to transmit the thermal state signal and the local oscillator signal respectively, there is no need to perform time division, wavelength division and polarization multiplexing, and there is no need to perform pulse modulation. Alice and Bob can realize interference of continuous thermal state signals and continuous coherent light signals, and use high-bandwidth quantum balanced homodyne detection and high-bandwidth data acquisition cards to obtain initial key data at high speed, thereby realizing high-code-rate continuous-variable quantum key distribution.

[0080] Since two optical fibers are used to transmit the thermal state signal and the local oscillator signal respectively, there is no need to perform time division, wavelength division and polarization multiplexing, and there is no need to perform pulse modulation. Alice and Bob can realize interference of continuous thermal state signals and continuous coherent light signals, and use high-bandwidth quantum balanced homodyne detection and high-bandwidth data acquisition cards to obtain initial key data at high speed, thereby realizing high-code-rate continuous-variable quantum key distribution.

[0081] The high-bandwidth quantum balanced homodyne detector in the embodiment is, for example, a product PDB435C of Thorlabs Company. The ASE in the embodiment is, for example, a product ASE Light Source of Golight Company. The optical amplifier in the embodiment is, for example, a product KY-EDFA-0-30-D-FA of Kyon Optoelectronics Company.

[0082] The continuous data post-processing step specifically includes the following steps:

[0083] (1) Bob and Alice perform bit frame synchronization of the initial continuous key data without special modulation frames, and perform block phase compensation based on data processing.

[0084] The bit frame synchronization without special modulation frames can be implemented by those skilled in the art by learning the prior art, for example, the bit frame synchronization without special modulation frames can be implemented by referring to the “quantum key distribution system non-special frame bit frame synchronization method and system” (application number: 2019106418841, publication number: CN110213034A) disclosed in the Chinese invention patent document. In the patent document, the bit frame synchronization without special modulation frames is referred to as the “quantum key distribution system non-special frame bit frame synchronization method”.

[0085] The data processing-based block phase compensation can be implemented by those skilled in the art by learning the prior art, for example, the data processing-based phase compensation can be implemented by referring to the quantum key distribution system phase compensation method (application number 201410567665.0, publication number CN104301101A) disclosed in the Chinese invention patent document. In the patent document, the data processing-based phase compensation is referred to as the quantum key distribution system phase compensation. For the block phase compensation, the main purpose is to optimize the compensation algorithm of the large data block formed by the code under the phase instability condition, which can significantly reduce the data over noise when the optical path is unstable.

[0086] (2) Alice and Bob publish part of the initial key data for parameter evaluation, and obtain the signal over noise, modulation variance and channel transmission rate parameters.

[0087] (3) Bob corrects the initial continuous key data after phase compensation by using the high-efficiency multi-dimensional negotiation algorithm based on LDPC coding, and outputs consistent binary shared key string.

[0088] The high-efficiency multi-dimensional negotiation algorithm based on LDPC coding is a prior art, and those skilled in the art can implement the high-efficiency multi-dimensional negotiation algorithm based on LDPC coding by learning the prior art, for example, learning the paper "A. Leverrier, et al, Multidimensional reconciliation for a continuous-variable quantum key distribution. Phys. Rev. A 77(4), 042325 (2008)." In the paper, the high-efficiency multi-dimensional negotiation algorithm based on LDPC coding is referred to as "Multidimensional reconciliation".

[0089] (4) Bob calculates the Holevo limit and the mutual information of the legal communication party by using the channel parameters, obtains the information compression rate, and finally outputs the final key by using the security enhancement. The calculation method is a known technology, for example, those skilled in the art can implement the calculation by referring to the paper "Weedbrook, C. et al. Gaussian quantum information. Rev. Mod. Phys. 84, 621 (2012)".

[0090] The present application optimizes the sending end source of CVQKD, coding modulation, polarization multiplexing, bit frame synchronization and over noise control technology, is used for low cost and simplification of existing Gaussian modulation coherent state CVQKD system and its implementation, and improves the security code rate performance of CVQKD in short distance free space.

[0091] Specifically, not only the natural fluctuation of thermal light can be used to match the light field after Gaussian modulation of coherent light, but also the scheme equivalent to Gaussian modulation based continuous variable quantum key distribution can be realized, and only part of the preparation noise is increased, and these additional preparation noises can also be controlled by controlling the average photon number and attenuation coefficient of the thermal light source. By introducing a multi-round bit frame synchronization algorithm without special frame modulation, an efficient negotiation algorithm, a high-bandwidth quantum balanced heterodyne detector, high-speed data acquisition and a phase compensation algorithm based on data processing, CVQKD without quantum random number and intensity and phase modulation can be realized. It is worth noting that the multi-round bit frame synchronization algorithm without special frame modulation of the present application is aimed at the key data of both parties measured after polarization multiplexing, and has good adaptability to the channel characteristics jitter of free space channel, and is a key technical breakthrough for realizing safe coding based on thermal light source for free space channel transmission. The realized free space channel based on thermal source on-the-fly local oscillator continuous variable quantum key distribution method can realize high-speed and widely applicable continuous variable quantum key distribution with relatively simple experimental scheme and device cost.

[0092] In summary, the free space continuous variable quantum key distribution method and system based on a thermal source provided by the embodiment of the present application can directly use a thermal light source in a free space channel to realize Gaussian modulation coherent state continuous variable quantum key distribution without intensity and phase modulators and random number sources, thereby reducing the implementation complexity of the continuous variable quantum key distribution system and providing a new application scenario for the quantum key distribution system.

[0093] Those skilled in the art know that, in addition to implementing the system provided by the present application and each device, module and unit thereof in the form of pure computer readable program code, the system provided by the present application and each device, module and unit thereof can also be implemented in the form of logic gates, switches, application specific integrated circuits, programmable logic controllers and embedded microcontrollers, etc. by logically programming the method steps to achieve the same functions. Therefore, the system provided by the present application and each device, module and unit thereof can be considered as a hardware component, and the devices, modules and units included therein for achieving various functions can also be considered as structures within the hardware component; the devices, modules and units for achieving various functions can also be considered as both software modules implementing methods and structures within hardware components.

[0094] The specific embodiments of the present application are described above. It needs to be understood that the present application is not limited to the specific embodiments described above, and various changes or modifications can be made by those skilled in the art within the scope of the claims, which does not affect the essential content of the present application. The embodiments of the present application and the features in the embodiments can be combined with each other in any manner without conflict.

Claims

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The application relates to a continuous-variable quantum key distribution method and device. The application relates to Step S2.3: Bob corrects errors of the initial continuous key data after phase compensation by a high-efficiency multi-dimensional negotiation algorithm based on LDPC coding, and outputs a consistent binary shared key string; Step S2.4: Bob calculates Holevo limit and mutual information of a legal communication party through channel parameters, obtains an information compression rate, and finally outputs a final key through security enhancement.

2. The thermal source based free-space continuous-variable quantum key distribution method of claim 1, wherein, Isolators, photodetectors PD and optical power meters are arranged in the optical paths of Alice and Bob to monitor the light intensity of the thermal light source and the local oscillator light.

3. A thermal source based free-space continuous variable quantum key distribution system, characterized in that, Comprise: Continuous variable initial key distribution module: the detection results of the regular components X and P of the thermal light source after polarization beam splitting by the sender Alice are taken as the local initial key; And the other half of the thermal light signal is attenuated, combined with the local oscillator light, transmitted through the free space channel, and detected by the receiver Bob to obtain the corresponding initial continuous key data; Continuous data post-processing module: Bob performs bit frame synchronization, block phase compensation, parameter evaluation, error correction and security enhancement on the obtained initial continuous key data, and finally obtains a secure binary bit key; The continuous variable initial key distribution module comprises: Module M1.1: the sender Alice and the receiver Bob initialize the continuous variable quantum key distribution system based on the thermal light source, including initializing the ASE thermal source, the coherent light source, the optical amplifier, the optical bandpass filter, the polarization beam splitter, the 90° optical hybrid, the quantum balanced homodyne detector and the control circuit in the system; Module M1.2: the Alice end amplifies the ASE thermal source through the optical amplifier, passes through the narrowband optical filter, and is divided into two paths through the 50:50 optical beam splitter, one path is attenuated through the optical attenuator and combined with the local oscillator signal as the receiving end local oscillator light through the 50:50 optical beam splitter of the coherent light source to send to the receiver Bob, and the other path is left in the local and input into the optical hybrid with the other half of the coherent light signal at the same time to perform quantum balanced homodyne detection, and the regular components X and P of the thermal light are obtained as the initial key data K1; Module M1.3: Bob demultiplexes the polarization multiplexed signal sent by Alice into local oscillator signals and thermal signals, respectively inputs the optical hybrid through polarization control to perform quantum balanced homodyne detection, and obtains the regular components X and P of the received thermal light as the initial key data K2; The module M1.2 comprises: Module M1.2.1: Alice adjusts the ASE thermal source, the optical amplifier and the optical attenuator to control the average photon number, so that the average photon number of the thermal light signal passing through the 50:50 optical beam splitter and the attenuator satisfies n=0.5mn0; Wherein, m is the attenuation factor of the optical attenuator, n0 is the average photon number of the thermal state optical signal after the band-pass filter, and the thermal state canonical component obeys the Gaussian distribution with the mean value of zero and the variance of V A = mn0; wherein, V A The value range of V is greater than 0 and less than 80, and it is sent to Bob through the free space channel. Module M1.2.2: Alice retains the other half of the hot optical signal branched by the 50:50 optical beam splitter locally, and inputs the part of the optical signal branched by the 50:50 optical beam splitter and the continuous coherent optical signal generated by Alice into the Hybrid optical mixer at the same time, realizes the interference of the two continuous optical signals, and obtains the initial key data X through the quantum balanced homodyne detector, and the other part is sent to Bob together with the signal light through polarization beam combining; The continuous data post-processing module comprises: Module M2.1: Bob and Alice perform multi-round bit frame synchronization of the initial continuous key data without special modulation frames, and perform phase compensation based on data processing; Module M1.2: Alice and Bob publish part of the initial key data for parameter evaluation, and obtain signal noise, modulation variance and channel transmission rate parameters; Module M1.3: Bob corrects the initial continuous key data after phase compensation through an efficient multi-dimensional negotiation algorithm based on LDPC coding, and outputs consistent binary shared key strings; Module M1.4: Bob calculates the Holevo limit and the mutual information of the legitimate communication party through the channel parameters, obtains the information compression rate, and finally outputs the final key through security enhancement.

4. The thermal source based free-space continuous-variable quantum key distribution system of claim 3, wherein, Isolators, optical detectors PD and optical power meters are arranged in the optical paths of Alice and Bob to monitor the light intensity of the hot light source and the local oscillator light.

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