Local local oscillator free space continuous variable quantum key distribution method and system

Abstract

The invention provides a local local oscillator free space continuous variable quantum key distribution method and system, and the method comprises the steps: S1, a sender carries out heterodyne detection on a part of thermal state optical signals after polarization splitting of a thermal state light source, employs a detection result as a local initial key, and employs the other part of thermal state optical signals as signal light after attenuation; meanwhile, the local oscillation light is subjected to beam splitting, one part is used for executing heterodyne detection, the other part and the signal light are combined in the same polarization direction, homodyne or heterodyne detection is carried out by a receiver after transmission is carried out through a free space channel, and corresponding initial continuous key data are obtained; and S2, the receiver executes data frame synchronization, frequency offset compensation, phase compensation, parameter evaluation, error correction and confidentiality enhancement on the obtained initial continuous key data to obtain a binary bit key. The invention provides a continuous variable quantum key distribution scheme under a free space channel, and the average key rate under a-23dB attenuation channel can reach an Mbps magnitude.

Description

Technical Field

[0001] This invention relates to the field of quantum key distribution, and more specifically, to a local oscillator free-space continuous-variable quantum key distribution method and system. Background Technology

[0002] Most current continuous-variable quantum key distribution (CVQKD) systems utilize amplitude and phase modulators to modulate and encode random key information generated by a quantum true random number generator onto weakly coherent light for key distribution. For example, Gaussian modulation quantum key distribution (GMCS-CVQKD) uses amplitude and phase modulators to modulate Gaussian-distributed quantum true random numbers onto the canonical components of weakly coherent light, and then transmits it to the receiver via fiber optic or free-space channels. Discrete-variable quantum key modulation (DVQKD) systems also modulate a finite number of quantum states using amplitude and phase modulators, and then transmit the modulated data to the receiver for demodulation and detection. Both methods require not only quantum true random number generators but also active amplitude and phase modulators to achieve linear modulation of the optical signal. However, the operation of practical devices often exhibits nonlinear effects, preventing the initial key information from achieving linear modulation on the optical field components, thus affecting system implementation. Furthermore, in the field of quantum key distribution based on hot-state light sources, there is no mature quantum key distribution scheme for either fiber optic or free-space channels.

[0003] Patent document CN117118611A discloses a high-code-rate continuous-variable quantum key distribution system with local oscillator fiber, including a continuous-variable initial key distribution step. Specifically, the sender Alice performs heterodyne detection on half of the hot-state light signal after biasing and splitting the hot-state light source, using the results X and P as local initial keys. The other half of the hot-state light signal is attenuated and combined with the local oscillator light, transmitted through a free-space channel, and then the receiver Bob performs null or heterodyne detection to obtain the corresponding initial continuous key data. The data post-processing step specifically involves the receiver Bob performing data frame synchronization, phase compensation, parameter evaluation, error correction, and security enhancement on the obtained initial continuous key data to obtain a binary bit key. However, this patent does not suppress excessive noise in various parts of the system and cannot solve the problem of continuous-variable quantum key distribution with a hot-state light source in a high-attenuation channel.

[0004] Patent application CN115459904A discloses a bidirectional continuous-variable quantum key distribution method based on a local oscillator, comprising: step S1: generating pulse sources at two user terminals respectively, and splitting the pulse light into a signal source and a local oscillator source using a beam splitter; step S2: modulating the signal source at both user terminals; step S3: transmitting quantum signals at both user terminals and receiving the quantum signals sent by the other; step S4: using the local oscillator light for coherent detection to extract the key at both user terminals. However, this patent cannot completely solve the existing technical problems, nor can it meet the needs of this invention. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a local oscillator free-space continuous-variable quantum key distribution method and system.

[0006] The local oscillator free-space continuous-variable quantum key distribution method provided by the present invention includes: Step S1: The sender performs heterodyne detection on a portion of the thermal light signal after polarization and beam splitting, uses the detection result as the local initial key, and attenuates another portion of the thermal light signal as the signal light; at the same time, the local oscillator light is split, one part is used to perform heterodyne detection, and the other part is combined with the signal light in the same polarization direction. After being transmitted through the free space channel, the receiver performs null or heterodyne detection to obtain the corresponding initial continuous key data. Step S2: The receiver performs data frame synchronization, frequency offset compensation, phase compensation, parameter evaluation, error correction and security enhancement on the obtained initial continuous key data to obtain the binary bit key.

[0007] Preferably, in step S1: Step S1.1: The sender and receiver perform communication initialization on the local oscillator free space continuous variable quantum key distribution system based on the thermal source, including initializing the ASE thermal source, optical bandpass filter, polarizer, polarization-maintaining beam splitter, integrated coherent detector and control circuit in the system. Step S1.2: The transmitting end amplifies the thermal light signal generated by the ASE thermal light source through an optical amplifier and then passes it through a narrowband optical filter to obtain a thermal light signal with a wavelength concentrated at 1550.12nm. The signal is then split into two beams by a 90:10 optical beam splitter. The stronger beam and a portion of the local oscillator light signal generated by the 1550.12nm laser source through a 50:50 optical beam splitter are simultaneously input into an integrated coherent detector to perform heterodyne detection. The canonical components X and P of the detection result are used as the initial key Key1. The weaker beam is attenuated by an optical attenuator and then combined with another portion of the local oscillator light signal, which is used as a pilot after passing through an attenuator, through a polarization-maintaining beam combiner to be in the same polarization direction. The beams are then transmitted to the receiving end through a free space channel. Step S1.3: After the receiver adjusts the polarization of the optical signal sent by the transmitter, it inputs it together with the light output from another laser adjusted to 1550.13nm into an integrated coherent detector to perform heterodyne detection, and obtains the regular component X or P of the received thermal optical signal as the initial key data Key2.

[0008] Preferably, in step S2: Step S2.1: The receiver obtains the beat frequency signal and the key signal through bandpass and bandstop filtering, respectively; Step S2.2: The receiver and sender perform frame synchronization of the initial continuous key data to obtain the original synchronization data; Step S2.3: The receiver performs frequency offset recovery and phase recovery on the received key signal using the beat frequency signal, and uses the beat frequency signal to perform real-time transmittance evaluation; Step S2.4: The sender and receiver publish part of the initial key data for parameter evaluation to obtain the noise and modulation variance parameters; Step S2.5: The receiver calculates the Holevo limit and the mutual information of the legitimate communicating parties through the channel parameters, obtains the information compression rate, and outputs the final key through security enhancement.

[0009] Preferably, in step S1.2: Step S1.2.1: The transmitter controls the over-noise by adjusting the ASE light source and the optical attenuator, so that the over-noise is less than 0.005. At this time, the modulation variance VA is greater than 0 and less than 20, where VA = 0.5n0, and n0 is the average number of photons of the thermal optical signal after passing through the bandpass filter. Step S1.2.2: The sender retains the stronger thermal optical signal after splitting by the 90:10 optical beam splitter locally, and inputs it simultaneously with a portion of the local oscillator signal after splitting by the 1550.12nm local oscillator signal generated by the laser through a 50:50 optical beam splitter into a hybrid mixer to achieve interference between the two continuous optical signals. The initial key data, which is the value of the canonical components X and P of the thermal optical signal, is obtained through an integrated coherent detector. The other thermal optical signal is combined with the local oscillator signal used as a pilot signal through a polarization-maintaining beam combiner and then sent to the receiver.

[0010] Preferably, in step S2.3: Step S2.3.1: For each experiment, the receiver detects and acquires time-varying frequency offset and phase drift data in real time through the beat frequency signal, and compensates and recovers the received key signal based on the above measurement results; Step S2.3.2: Perform low-pass filtering on the key signal after frequency offset and phase drift compensation to extract the effective beat frequency signal, and calculate and record the power value at each moment based on the signal in real time; Step S2.3.3: In the pre-calibration stage, an optical fiber is used to establish a connection link between the sender and receiver. Steps S1 and S2 are executed to obtain and store the pre-calibration beat frequency power reference value in this state. Step S2.3.4: By comparing the real-time acquisition of the beat frequency signal power value in step S2.3.2 with the pre-calibrated beat frequency power reference value stored in step S2.3.3, the power difference between the two is calculated, and the real-time transmittance estimate of the channel is finally obtained.

[0011] The local oscillator free-space continuous-variable quantum key distribution system provided by the present invention includes: Module M1: The sender performs heterodyne detection on a portion of the thermal light signal after polarization and beam splitting from the thermal light source, uses the detection result as the local initial key, and attenuates another portion of the thermal light signal as the signal light; at the same time, the local oscillator light is split, one part is used for heterodyne detection, and the other part is combined with the signal light in the same polarization direction. After being transmitted through the free space channel, the receiver performs null or heterodyne detection to obtain the corresponding initial continuous key data. Module M2: The receiver performs data frame synchronization, frequency offset compensation, phase compensation, parameter evaluation, error correction, and security enhancement on the obtained initial continuous key data to obtain the binary bit key.

[0012] Preferably, in module M1: Module M1.1: The sender and receiver perform communication initialization for the local oscillator free space continuous variable quantum key distribution system based on the thermal source, including initializing the ASE thermal source, optical bandpass filter, polarizer, polarization-maintaining beam splitter, integrated coherent detector and control circuit in the system; Module M1.2: The transmitting end amplifies the thermal light signal generated by the ASE thermal light source through an optical amplifier, and then passes it through a narrowband optical filter to obtain a thermal light signal with a wavelength concentrated at 1550.12nm. The signal is then split into two beams by a 90:10 optical beam splitter. The stronger beam and a portion of the local oscillator light signal generated by the 1550.12nm laser source after being split by a 50:50 optical beam splitter are simultaneously input into an integrated coherent detector to perform heterodyne detection. The initial key Key1 is obtained based on the canonical components X and P of the detection result. The weaker beam is attenuated by an optical attenuator and then combined with another portion of the local oscillator light signal, which is used as a pilot by the attenuator, through a polarization-maintaining optical beam combiner to be in the same polarization direction. The beams are then transmitted to the receiving end through a free space channel. Module M1.3: After the receiver adjusts the polarization of the optical signal sent by the transmitter, it inputs it together with the light output from another laser adjusted to 1550.13nm into an integrated coherent detector to perform heterodyne detection, and obtains the canonical component X or P of the received thermal optical signal as the initial key data Key2.

[0013] Preferably, in module M2: Module M2.1: The receiver obtains the beat frequency signal and the key signal through bandpass and bandstop filtering, respectively; Module M2.2: The receiver and sender perform frame synchronization of initial continuous key data and obtain the original synchronization data; Module M2.3: The receiver performs frequency offset recovery and phase recovery on the received key signal using the beat frequency signal, and uses the beat frequency signal to perform real-time transmittance evaluation; Module M2.4: The sender and receiver publish part of the initial key data for parameter evaluation to obtain the noise and modulation variance parameters; Module M2.5: The receiver calculates the Holevo limit and mutual information of legitimate communicators through channel parameters, obtains the information compression rate, and outputs the final key through security enhancement.

[0014] Preferably, in module M1.2: Module M1.2.1: The transmitter controls the over-noise by adjusting the ASE light source and the optical attenuator, so that the over-noise is less than 0.005. At this time, the modulation variance VA is greater than 0 and less than 20, where VA = 0.5n0, and n0 is the average number of photons of the thermal optical signal after passing through the bandpass filter. Module M1.2.2: The sender retains the stronger thermal optical signal from the 90:10 optical beam splitter locally and inputs it into a hybrid mixer along with a portion of the local oscillator signal obtained from the 1550.12nm local oscillator signal generated by the laser, which is split by a 50:50 optical beam splitter. This achieves interference between the two continuous optical signals. The initial key data X is obtained through an integrated coherent detector. This data is the value of the canonical component X and P of the thermal optical signal. The other signal is combined with the local oscillator signal used as a pilot signal through a polarization-maintaining beam combiner and then sent to the receiver.

[0015] Preferably, in module M2.3: Module M2.3.1: For each experiment, the receiver detects and acquires time-varying frequency offset and phase drift data in real time through beat frequency signal, and compensates and recovers the received key signal based on the above measurement results; Module M2.3.2: Performs low-pass filtering on the key signal after frequency offset and phase drift compensation, extracts the effective beat frequency signal, and calculates and records the power value at each moment in real time based on the signal; Module M2.3.3: During the pre-calibration phase, an optical fiber is used to establish a connection link between the sender and receiver, triggering modules M1 and M2 to acquire and store the pre-calibration beat frequency power reference value in this state; Module M2.3.4: By comparing the real-time acquisition of the beat frequency signal power value in module M2.3.2 with the pre-calibrated beat frequency power reference value stored in module M2.3.3, the power difference between the two is calculated, and finally the real-time transmittance estimate of the channel is obtained.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. The method provided by this invention can realize secure coding of local oscillator free space CVQKD based on thermal source. It is currently the continuous variable quantum key distribution scheme under high attenuation free space channel. The average key rate can reach the Mbps level under -23dB attenuation channel. 2. This invention uses a high-bandwidth detector, which fully reflects the characteristics of thermal signals and greatly improves the system key rate; 3. This invention uses a post-processing algorithm based on continuous mode theory, which can perform real-time transmittance evaluation and high-precision phase recovery and frequency offset recovery. Attached Figure Description

[0017] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a schematic diagram of a local oscillator free-space continuous-variable quantum key distribution method based on a thermal source.

[0018] Among them: ASE (amplified spontaneous emission) is an amplified spontaneous emission heat source. The Alice end contains a 50:50 beam splitter and a 90:10 beam splitter, which split the input local oscillator light and signal light into two paths respectively. One of the local oscillator light beams is split and the stronger signal light beam is split and input into an integrated coherent detector for heterodyne detection. The Bob end uses a polarization controller to control the polarization state of the signal light, and then inputs the signal light and the local oscillator light generated by the local laser into an integrated coherent detector for heterodyne detection. Detailed Implementation

[0019] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0020] Example 1 This invention proposes a complete implementation method for local oscillator free-space continuous-variable quantum key distribution based on a thermal source. This method not only utilizes the inherent random fluctuations of the thermal source to generate true random quantum numbers, eliminating the need for a random number generator and amplitude and phase modulators, but also only adds some preparation noise. This additional preparation noise can be suppressed by controlling the average photon number of the thermal source, the beam splitting ratio of the signal light, and the attenuation coefficient in the optical path. Notably, by increasing the beam splitting ratio and the attenuation coefficient, the total noise of quantum key distribution based on the thermal source is reduced. The use of frequency offset recovery and phase recovery algorithms based on continuous optical pilots represents a key technological breakthrough in quantum key distribution schemes based on local oscillator free-space channel transmission using a thermal source.

[0021] In summary, the realized local oscillator free-space continuous-variable quantum key distribution scheme based on thermal sources can achieve continuous-variable quantum key distribution with relatively simple experimental schemes and relatively low device costs, and has wide application value.

[0022] This invention relates to quantum key distribution, specifically to a local oscillator free-space continuous-variable quantum key distribution (CVQKD) method based on a thermal source, and particularly to a method for implementing a free-space CVQKD system with reduced cost and simplified implementation by optimizing the transmitter source, polarization multiplexing, photoelectric detection, and over-noise control techniques. This method utilizes the canonical components generated by the inherent random fluctuations of the thermal light source to achieve random encoding of the non-commuting optical field components in continuous-variable quantum cryptography. Although this effectively increases the over-noise in the preparation of some encoded signals, it achieves continuous-variable quantum key distribution in a free-space channel without requiring a quantum true random number generator or amplitude and phase modulators.

[0023] This invention provides a local oscillator free-space continuous-variable quantum key distribution method based on a thermal source. The specific process includes: Step A: The initial continuous-variable key distribution step using a thermal source involves the sender Alice performing heterodyne detection on the thermal source, combining the beams using a polarization beam splitter, and then transmitting the beams in a free-space channel via polarization multiplexing. The receiver Bob then performs polarization demultiplexing and performs homodyne detection to obtain initial continuous key data. Step B: This involves using a data post-processing algorithm to preprocess, correct errors, and enhance security of the obtained initial continuous key data to obtain the final secure binary bit key. This invention can directly implement continuous-variable quantum key distribution using a thermal source in a free-space channel without the need for intensity and phase modulators and random number sources, reducing the implementation complexity of the continuous-variable quantum key distribution system while achieving high key rate continuous-variable quantum key distribution.

[0024] A local oscillator free-space continuous-variable quantum key distribution method provided by the present invention, such as Figure 1 As shown, the process includes: Step S1: The sender Alice performs heterodyne detection on 90% of the hot-state optical signal after polarization and beam splitting from the hot-state light source, using the results X and P as the local initial key, and attenuating the remaining 10% of the hot-state optical signal as the signal light. Simultaneously, the local oscillator light is split, with 50% used for heterodyne detection and the remaining 50% combined with the signal light in the same polarization direction. After transmission through a free-space channel, the receiver Bob performs null or heterodyne detection to obtain the corresponding initial continuous key data; Step S2: The receiver Bob performs data frame synchronization, frequency offset compensation, phase compensation, parameter evaluation, error correction, and security enhancement on the obtained initial continuous key data to obtain the binary bit key.

[0025] In step S1: Step S1.1: The sender Alice and the receiver Bob perform communication initialization of the local oscillator free-space continuous-variable quantum key distribution system based on the thermal source, including initializing the ASE thermal source, optical bandpass filter, polarizer, polarization-maintaining beam splitter, integrated coherent detector, and control circuit in the system; Step S1.2: Alice amplifies the thermal light signal generated by the ASE thermal source through an optical amplifier and then passes it through a narrowband optical filter to obtain a thermal light signal with a wavelength concentrated at 1550.12nm. This signal is then split into two beams by a 90:10 optical beam splitter. The stronger beam is combined with the light generated by the 1550.12nm laser source and then split into two beams by a 50:10 optical beam splitter. A portion of the local oscillator light signal from the 50nm optical beam splitter is simultaneously input into the integrated coherent detector to perform heterodyne detection. The normalized components X and P of the detection result are used to obtain the initial key Key1. The weaker beam is attenuated by an optical attenuator and then combined with another portion of the local oscillator light signal, which is used as a pilot after passing through an attenuator, through a polarization-maintaining beam combiner to be in the same polarization direction. The beam is then sent to the receiver Bob through a free-space channel. Step S1.3: The receiver Bob adjusts the polarization of the light signal sent by Alice and inputs it together with another laser adjusted to 1550.13nm into the integrated coherent detector to perform heterodyne detection. The normalized component X or P of the received hot-state light signal is used as the initial key data Key2.

[0026] Without time-division or wavelength-division multiplexing, and without pulse modulation, the transmitter Alice and receiver Bob achieve interference between the continuous hot-state signal light and the local oscillator light signal, and use a photoelectric detector and oscilloscope to acquire the initial key data at high speed, thus realizing continuous variable quantum key distribution.

[0027] In step S1.2: Step S1.2.1: The transmitter Alice controls the over-noise by adjusting the ASE light source and the optical attenuator, so that the over-noise is less than 0.005. At this time, the modulation variance VA is greater than 0 and less than 20, where VA = 0.5n0, and n0 is the average number of photons of the thermal optical signal after passing through the bandpass filter; Step S1.2.2: The transmitter Alice retains the stronger thermal optical signal from the 90:10 optical beam splitter locally, and inputs it into the Hybrid mixer along with a portion of the local oscillator signal from the 1550.12nm local oscillator signal generated by the laser through the 50:50 optical beam splitter, so as to realize the interference of the two continuous optical signals. The initial key data X is obtained by the integrated coherent detector, which is the value of the regular component X and P of the thermal optical signal. The other path is combined with the local oscillator signal used as the pilot by the polarization-maintaining beam combiner and sent to the receiver Bob.

[0028] In step S2: Step S2.1: Receiver Bob obtains the beat frequency signal and key signal through bandpass and bandstop filtering, respectively; Step S2.2: Receiver Bob and sender Alice perform frame synchronization of initial continuous key data to obtain the original synchronization data; Step S2.3: Receiver Bob performs frequency offset recovery and phase recovery on the received key signal through the beat frequency signal, and uses the beat frequency signal for real-time transmittance evaluation; Step S2.4: Sender Alice and receiver Bob publish part of the initial key data for parameter evaluation to obtain over-noise and modulation variance parameters; Step S2.5: Receiver Bob calculates the Holevo limit and mutual information of legitimate communicators through channel parameters to obtain the information compression rate, and outputs the final key through security enhancement.

[0029] In step S2.3: Step S2.3.1: For each experiment, the receiver Bob needs to detect and acquire time-varying frequency offset and phase drift data in real time through the beat frequency signal. Based on the above measurement results, the received key signal is compensated and recovered. Step S2.3.2: Low-pass filtering is performed on the key signal after frequency offset and phase drift compensation to extract the effective beat frequency signal. Based on this signal, the power value at each moment is calculated and recorded in real time. Step S2.3.3: In the pre-calibration stage, a connection link between Alice and Bob is established using the shortest possible optical fiber (the influence of channel attenuation can be ignored at this time). The operation is completed according to steps S1 and S2, and the pre-calibration beat frequency power reference value in this state is acquired and stored. Step S2.3.4: By comparing the beat frequency signal power value acquired in real time in step S2.3.2 with the pre-calibration beat frequency power reference value stored in step S2.3.3, the power difference between the two is calculated, and finally the real-time transmittance estimate of the channel is obtained.

[0030] Example 2 The present invention also provides a local oscillator free space continuous variable quantum key distribution system, which can be implemented by executing the process steps of the local oscillator free space continuous variable quantum key distribution method. That is, those skilled in the art can understand the local oscillator free space continuous variable quantum key distribution method as a preferred embodiment of the local oscillator free space continuous variable quantum key distribution system.

[0031] The system includes: In module M1: Module M1.1: The sender Alice and receiver Bob perform communication initialization for the local oscillator free-space continuous-variable quantum key distribution system based on a thermal source, including initializing the ASE thermal source, optical amplifier, optical bandpass filter, polarizer, polarization-maintaining beam splitter, integrated coherent detector, and control circuit in the system; Module M1.2: Alice amplifies the thermal light signal generated by the ASE thermal source through the optical amplifier and then passes it through a narrowband optical filter to obtain a thermal light signal with a wavelength concentrated at 1550.12nm. This signal is then split into two beams by a 90:10 beam splitter, with the stronger beam and the 1550.12nm laser beam splitter. A portion of the local oscillator light signal generated by the source and processed by a 50:50 optical beam splitter is simultaneously input into an integrated coherent detector to perform heterodyne detection. The normalized components X and P of the detection result are used to obtain the initial key Key1. The weaker beam is attenuated by an optical attenuator and then combined with another portion of the local oscillator light signal used as a pilot signal through a polarization-maintaining beam combiner to be in the same polarization direction. The beam is then sent to the receiver Bob through a free-space channel. Module M1.3: The receiver Bob adjusts the polarization of the light signal sent by Alice and inputs it together with another laser tuned to 1550.13nm into an integrated coherent detector to perform heterodyne detection. The normalized component X or P of the received hot-state light signal is used as the initial key data Key2.

[0032] In module M1: Module M1.1: The sender Alice and receiver Bob perform communication initialization for the local oscillator free-space continuous-variable quantum key distribution system based on a thermal source, including initializing the ASE thermal source, optical amplifier, optical bandpass filter, polarizer, polarization-maintaining beam splitter, integrated coherent detector, and control circuit in the system; Module M1.2: Alice amplifies the thermal light signal generated by the ASE thermal source through the optical amplifier and then passes it through a narrowband optical filter to obtain a thermal light signal with a wavelength concentrated at 1550.12nm. This signal is then split into two beams by a 90:10 optical beam splitter. The stronger beam is combined with the light generated by the 1550.12nm laser source. A portion of the local oscillator light signal from the 50:50 optical beam splitter is simultaneously input into the integrated coherent detector to perform heterodyne detection. The normalized components X and P of the detection result are used to obtain the initial key Key1. The weaker beam is attenuated by an optical attenuator and then combined with another portion of the local oscillator light signal, which is used as a pilot after passing through an attenuator, through a polarization-maintaining beam combiner to be in the same polarization direction. The beam is then sent to the receiver Bob through a free-space channel. Module M1.3: The receiver Bob adjusts the polarization of the light signal sent by Alice and inputs it together with another laser tuned to 1550.13nm into the integrated coherent detector to perform heterodyne detection. The normalized component X or P of the received hot-state light signal is used as the initial key data Key2.

[0033] Without time-division or wavelength-division multiplexing, and without pulse modulation, the transmitter Alice and receiver Bob achieve interference between the continuous hot-state signal light and the local oscillator light signal, and use a photoelectric detector and oscilloscope to acquire the initial key data at high speed, thus realizing continuous variable quantum key distribution.

[0034] In module M1.2: Module M2.2.1: The transmitter Alice controls the over-noise by adjusting the ASE light source and optical attenuator, making the over-noise less than 0.005. At this time, the modulation variance VA ranges from greater than 0 to less than 20, where VA = 0.5n0, and n0 is the average number of photons of the thermal optical signal after passing through the bandpass filter; Module M2.2.2: The transmitter Alice retains the stronger thermal optical signal from the 90:10 optical beam splitter locally, and inputs it into the Hybrid mixer along with a portion of the local oscillator signal from the 1550.12nm local oscillator signal generated by the laser, which is split by the 50:50 optical beam splitter, to achieve interference between the two continuous optical signals. The initial key data X is obtained through the integrated coherent detector, which is the value of the regular component X and P of the thermal optical signal. The other signal is combined with the local oscillator signal used as a pilot by the polarization-maintaining beam combiner and sent to the receiver Bob.

[0035] In module M2: Module M2.1: Receiver Bob obtains the beat frequency signal and key signal through bandpass and bandstop filtering, respectively; Module M2.2: Receiver Bob and sender Alice perform frame synchronization of initial continuous key data to obtain the original synchronization data; Module M2.3: Receiver Bob performs frequency offset recovery and phase recovery on the received key signal through the beat frequency signal, and uses the beat frequency signal for real-time transmittance evaluation; Module M2.4: Sender Alice and receiver Bob publish part of the initial key data for parameter evaluation to obtain over-noise and modulation variance parameters; Module M2.5: Receiver Bob calculates the Holevo limit and mutual information of legitimate communicators through channel parameters to obtain the information compression rate, and outputs the final key through security enhancement.

[0036] In module M2.3: Module M2.3.1: For each experiment, the receiver Bob needs to detect and acquire time-varying frequency offset and phase drift data in real time through the beat frequency signal. Based on the above measurement results, the received key signal is compensated and recovered; Module M2.3.2: Low-pass filtering is performed on the key signal after frequency offset and phase drift compensation to extract the effective beat frequency signal. Based on this signal, the power value at each moment is calculated and recorded in real time; Module M2.3.3: In the pre-calibration stage, the connection link between Alice and Bob is established using the shortest possible optical fiber (the influence of channel attenuation can be ignored at this time). The operations are completed according to modules M1 and M2 to acquire and store the pre-calibration beat frequency power reference value in this state; Module M2.3.4: By comparing the beat frequency signal power value acquired in real time in module M2.3.2 with the pre-calibration beat frequency power reference value stored in module M2.3.3, the power difference between the two is calculated, and finally the real-time transmittance estimate of the channel is obtained.

[0037] Those skilled in the art will understand that, in addition to implementing the system, apparatus, and their modules provided by this invention in purely computer-readable program code, the same program can be implemented in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, the system, apparatus, and their modules provided by this invention can be considered a hardware component, and the modules included therein for implementing various programs can also be considered structures within the hardware component; alternatively, modules for implementing various functions can be considered both software programs implementing the method and structures within the hardware component.

[0038] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A local oscillator free free-space continuous-variable quantum key distribution method, characterized in that, Comprise: Step S1: the sender performs heterodyne detection on a part of the thermal light signal after the thermal light source is polarized and split, takes the detection result as the local initial key, and attenuates another part of the thermal light signal as the signal light; at the same time, the local light is split, one part is used to perform heterodyne detection, and the other part is combined with the signal light in the same polarization direction, and after transmission through the free space channel, it is detected by the receiver for homodyne or heterodyne detection to obtain the corresponding initial continuous key data; Step S2: the receiver performs data frame synchronization, frequency offset compensation, phase compensation, parameter evaluation, error correction and security enhancement on the obtained initial continuous key data to obtain a binary bit key.

2. The local oscillator free free-space continuous-variable quantum key distribution method of claim 1, wherein, In the step S1: Step S1.1: the sender and the receiver initialize the local local free space continuous variable quantum key distribution system based on the thermal source, including initializing the ASE thermal light source, optical band pass filter, polarizer, polarization maintaining optical splitter, integrated coherent detector and control circuit in the system; Step S1.2: the sender end amplifies the thermal light signal generated by the ASE thermal light source through the optical amplifier, and then passes through the narrowband optical filter to obtain the thermal light signal with the wavelength concentrated at 1550.12nm, and then passes through the 90:10 optical splitter to divide it into two beams, one stronger beam and the part of the local light signal generated by the 50:50 optical splitter of the 1550.12nm laser source are input into the integrated coherent detector to perform heterodyne detection, and the detection result is regular component X and P to obtain the initial key Key1, and the other weaker beam is attenuated by the optical attenuator, and then combined with the other part of the local light signal as the pilot after the polarization maintaining optical combiner to the same polarization direction, and then sent to the receiver through the free space channel; Step S1.3: the receiver end adjusts the polarization of the optical signal sent by the sender, and then inputs the adjusted optical signal and another laser adjusted to 1550.13nm into the integrated coherent detector to perform heterodyne detection, and takes the regular component X or P of the received thermal light signal as the initial key data Key2. 3.The local oscillator free free-space continuous-variable quantum key distribution method of claim 1, wherein, In the step S2: Step S2.1: the receiver obtains the beat frequency signal and the key signal by band pass filtering and band stop filtering respectively; Step S2.2: the receiver and the sender perform frame synchronization on the initial continuous key data to obtain the original synchronization data; Step S2.3: the receiver performs frequency offset recovery and phase recovery on the received key signal through the beat frequency signal, and uses the beat frequency signal to evaluate the real-time transmittance; Step S2.4: the sender and the receiver publish part of the initial key data for parameter evaluation to obtain the noise and modulation variance parameters; Step S2.5: the receiver calculates the Holevo limit and the mutual information of the legal communication party through the channel parameters to obtain the information compression rate, and outputs the final key through security enhancement.

4. The local oscillator free free-space continuous-variable quantum key distribution method of claim 2, wherein, In the step S1.2: Step S1.2.1: The sender prepares the over noise control by adjusting the ASE light source and the optical attenuator, so that the prepared over noise is less than 0.005, at this time, the value range of the modulation variance VA is greater than 0 and less than 20, wherein VA = 0.5n0, n0 is the average photon number of the thermal light signal after the band pass filter; Step S1.2.2: The sender retains the stronger one of the two beams of thermal light signals split by the 90:10 optical splitter locally, and inputs the 1550.12 nm local oscillator light signal generated by the laser and the part of the local oscillator light signal split by the 50:50 optical splitter into the Hybrid mixer at the same time, realizes the interference of the two continuous light signals, and obtains the initial key data X through the integrated coherent detector, which is the value of the canonical component X and P of the thermal light signal, and the other part is sent to the receiver through the polarization maintaining optical combiner after being combined with the local oscillator light as the pilot.

5. The local oscillator free free-space continuous-variable quantum key distribution method of claim 3, wherein, In the step S2.3: Step S2.3.1: For each experiment, the receiver detects and obtains the time-varying frequency offset and phase drift data in real time through the beat signal, and compensates and recovers the received key signal based on the above measurement results; Step S2.3.2: Perform low-pass filtering on the key signal after completing the frequency offset and phase drift compensation, extract the effective beat signal, and calculate and record the power value at each time based on the signal in real time; Step S2.3.3: In the pre-calibration stage, the connection link between the sender and the receiver is established by using an optical fiber, steps S1 and S2 are performed, and the pre-calibration beat frequency power reference value in this state is obtained and stored; Step S2.3.4: By comparing the beat signal power value collected in real time in step S2.3.2 with the pre-calibration beat frequency power reference value stored in step S2.3.3, the power difference value of the two is calculated, and finally the real-time transmission rate estimate value of the channel is obtained.

6. A local oscillator free free-space continuous variable quantum key distribution system, characterized in that, Comprise: Module M1: The sender performs heterodyne detection on a part of the thermal light signal split by the polarizing beam splitter, takes the detection result as the local initial key, and attenuates another part of the thermal light signal as the signal light; At the same time, the local oscillator light is split, one part is used for heterodyne detection, and the other part is combined with the signal light in the same polarization direction, transmitted through the free space channel, and then detected by the receiver for homodyne or heterodyne detection to obtain the corresponding initial continuous key data; Module M2: The receiver performs data frame synchronization, frequency offset compensation, phase compensation, parameter evaluation, error correction and security enhancement on the obtained initial continuous key data to obtain a binary bit key.

7. The local oscillator free free-space continuous-variable quantum key distribution system of claim 6, wherein, In the module M1: Module M1.1: The sender and the receiver initialize the local local oscillator free space continuous variable quantum key distribution system based on the thermal source, including initializing the ASE thermal light source, the optical band pass filter, the polarizer, the polarization maintaining optical splitter, the integrated coherent detector and the control circuit in the system; Module M1.2: the sender end amplifies the thermal light signal generated by the ASE thermal light source through the optical amplifier and then passes it through the narrow-band optical filter to obtain the thermal light signal with a wavelength of 1550.12 nm. The thermal light signal is divided into two beams by the 90:10 optical splitter. The stronger beam is input into the integrated coherent detector together with the local oscillator light signal generated by the 1550.12 nm laser source to perform heterodyne detection. The initial key Key1 is obtained from the quadrature components X and P of the detection result. The weaker beam is attenuated by the optical attenuator and then input into the polarization maintaining optical combiner together with the local oscillator light signal used as the pilot. The combined light is sent to the receiver through the free space channel. Module M1.3: the receiver end adjusts the polarization of the optical signal sent by the sender and inputs it into the integrated coherent detector together with another laser adjusted to 1550.13 nm to perform heterodyne detection. The quadrature components X or P of the received thermal light signal are obtained as the initial key data Key2.

8. The local oscillator free free-space continuous-variable quantum key distribution system of claim 6, wherein, In the module M2: Module M2.1: the receiver obtains the beat frequency signal and the key signal through bandpass and bandstop filtering, respectively; Module M2.2: the receiver and the sender perform frame synchronization of the initial continuous key data to obtain the original synchronization data; Module M2.3: the receiver performs frequency offset recovery and phase recovery on the received key signal through the beat frequency signal and evaluates the real-time transmittance using the beat frequency signal; Module M2.4: the sender and the receiver publish part of the initial key data for parameter evaluation to obtain the noise-over and modulation variance parameters; Module M2.5: the receiver calculates the Holevo limit and the mutual information of the legitimate communication party through the channel parameters to obtain the information compression rate and output the final key through security enhancement.

9. The local oscillator free free-space continuous-variable quantum key distribution system of claim 7, wherein, In the module M1.2: Module M1.2.1: the sender adjusts the ASE light source and the optical attenuator to prepare the noise-over control, so that the prepared noise-over is less than 0.

005. At this time, the value range of the modulation variance VA is greater than 0 and less than 20, where VA=0.5n0, n0 is the average photon number of the thermal light signal after bandpass filtering; Module M1.2.2: the sender retains the stronger beam of the thermal light signal split by the 90:10 optical splitter locally and inputs it into the Hybrid mixer together with the 1550.12 nm local oscillator light signal generated by the laser to realize the interference of the two continuous light signals. The initial key data X is obtained through the integrated coherent detector, which is the value of the quadrature component X and P of the thermal light signal. The other path is combined with the local oscillator light used as the pilot through the polarization maintaining optical combiner and then sent to the receiver.

10. The local oscillator free free-space continuous-variable quantum key distribution system of claim 8, wherein, In the module M2.3: Module M2.3.1: for each experiment, the receiver detects and obtains the time-varying frequency offset and phase drift data in real time based on the above measurement results. The received key signal is compensated and recovered. Module M2.3.2: Perform low-pass filtering on the key signal after completing the frequency offset and phase drift compensation, extract the effective beat frequency signal, and calculate and record the power value at each moment in real time based on the signal; Module M2.3.3: In the pre-calibration stage, use optical fiber to establish a connection link between the sender and the receiver, trigger module M1 and module M2, and obtain and store the pre-calibration beat frequency power reference value in this state; Module M2.3.4: Compare the beat frequency signal power value collected in real time in module M2.3.2 with the pre-calibration beat frequency power reference value stored in module M2.3.3, calculate the power difference value, and finally obtain the real-time transmission rate estimate value of the channel.

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