A timing error estimation method for dual polarization quantum key distribution

Abstract

The application discloses a timing error estimation method for dual-polarization quantum key distribution, which comprises the following steps: multiplexing a plurality of pilots on the spectrum of a first polarization and a second polarization of a communication signal respectively, transmitting the multiplexed communication signal through an optical fiber channel, and obtaining a receiving signal; obtaining a plurality of pilots and their phase information according to the receiving signal; and determining a timing error value and a delay value according to the phase information. The signal transmitted by the sending end in the application contains pilots capable of determining the timing error value and the delay value, and the receiving end can determine the timing error value and the delay value according to the pilots contained in the receiving signal. Even if the application is applied to a quantum communication system with weak signals, the timing error value and the delay value can be accurately determined, so that timing error estimation can be performed. The application is widely applied to the technical field of quantum communication.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of quantum communication, and particularly relates to a timing error estimation method for dual-polarization quantum key distribution. BACKGROUND

[0002] Quantum communication, like classical optical communication, also needs timing error estimation, which can accurately measure the amplitude and phase of the optical signal, and is crucial for accurate demodulation of communication signals, high-speed transmission, and improvement of signal quality and system performance. In particular, when dual-polarization quantum key distribution is performed, stable and reliable timing error estimation is more needed. However, the weak characteristics of quantum signals limit their transmission distance and bandwidth. Compared with classical optical communication, which can cover a distance from 10 kilometers to thousands of kilometers and a communication rate from 40 Gbps to 1 Tbps, the receiver bandwidth of quantum communication is usually between 20 GHz and 60 GHz. Therefore, the timing error estimation algorithms (clock synchronization algorithms) based on signal characteristics in classical optical communication, such as those relying on training sequences, are difficult to achieve good results in quantum communication. Moreover, due to non-ideal factors such as chromatic dispersion (CD), polarization mode dispersion (PMD), and random state of polarization (RSOP) in the optical fiber channel, the performance of traditional timing error estimation algorithms is limited when dealing with these complex channel effects. SUMMARY

[0003] In view of the technical problems that the timing error estimation technology for current classical optical communication applications is limited by non-ideal factors such as chromatic dispersion (CD), polarization mode dispersion (PMD), and random state of polarization (RSOP) in the optical fiber channel, and is difficult to achieve good results in quantum communication, the purpose of the present application is to provide a timing error estimation method for dual-polarization quantum key distribution.

[0004] In one aspect, the embodiments of the present application include a timing error estimation method for dual-polarization quantum key distribution applied to a sending end, which comprises the following steps:

[0005] Multiplexing a first pilot and a third pilot on the spectrum of a first polarization of a communication signal;

[0006] Multiplexing a second pilot and a fourth pilot on the spectrum of a second polarization of the communication signal;

[0007] Transmitting the multiplexed communication signal through an optical fiber channel.

[0008] Further, the frequency difference between the first pilot and the third pilot and the frequency difference between the second pilot and the fourth pilot are both equal to one-half of the baud rate of the communication signal.

[0009] Further, a frequency difference between the first pilot and the second pilot is equal to a frequency difference between the second pilot and the fourth pilot, and both are less than a half bit rate of the communication signal.

[0010] In another aspect, embodiments of the present application include a timing error estimation method for dual-polarization quantum key distribution applied to a receiving end, the timing error estimation method for dual-polarization quantum key distribution comprising the following steps:

[0011] Obtaining a receiving signal; the receiving signal is transmitted by a communication signal through an optical fiber channel, and the communication signal is multiplexed with a first pilot and a third pilot on a spectrum of a first polarization before being sent, and is multiplexed with a second pilot and a fourth pilot on a spectrum of a second polarization;

[0012] Obtaining the first pilot, the second pilot, the third pilot, the fourth pilot, a fifth pilot, a sixth pilot, a seventh pilot and an eighth pilot according to the receiving signal; wherein the fifth pilot is generated by a physical effect of the first pilot transmitting through the optical fiber channel, the sixth pilot is generated by a physical effect of the second pilot transmitting through the optical fiber channel, the seventh pilot is generated by a physical effect of the third pilot transmitting through the optical fiber channel, and the eighth pilot is generated by a physical effect of the fourth pilot transmitting through the optical fiber channel; the frequency of the fifth pilot is the same as the frequency of the first pilot, the frequency of the sixth pilot is the same as the frequency of the second pilot, the frequency of the seventh pilot is the same as the frequency of the third pilot, and the frequency of the eighth pilot is the same as the frequency of the fourth pilot;

[0013] Obtaining phase information of the first pilot, the second pilot, the third pilot, the fourth pilot, the fifth pilot, the sixth pilot, the seventh pilot and the eighth pilot;

[0014] According to the phase information, determining a timing error value and a delay value.

[0015] Further, the obtaining phase information of the first pilot, the second pilot, the third pilot, the fourth pilot, the fifth pilot, the sixth pilot, the seventh pilot and the eighth pilot comprises:

[0016] Down-converting the first pilot, the second pilot, the third pilot, the fourth pilot, the fifth pilot, the sixth pilot, the seventh pilot and the eighth pilot;

[0017] Filtering the down-converted pilots to obtain the phase information.

[0018] Further, the filtering the down-converted pilots to obtain the phase information comprises:

[0019] performing Wiener filtering on the down-converted pilot to obtain a phase of the first pilot, a phase of the second pilot, a phase of the third pilot, a phase of the fourth pilot, a phase of the fifth pilot, a phase of the sixth pilot, a phase of the seventh pilot, and a phase of the eighth pilot;

[0020] obtaining a first phase difference average value, the first phase difference average value being an average value of a phase difference between the first pilot and the third pilot and a phase difference between the sixth pilot and the eighth pilot;

[0021] obtaining a second phase difference average value, the second phase difference average value being an average value of a phase difference between the first pilot and the seventh pilot and a phase difference between the sixth pilot and the fourth pilot;

[0022] obtaining a third phase difference average value, the third phase difference average value being an average value of a phase difference between the fifth pilot and the third pilot and a phase difference between the second pilot and the eighth pilot;

[0023] obtaining a fourth phase difference average value, the fourth phase difference average value being an average value of a phase difference between the fifth pilot and the seventh pilot and a phase difference between the second pilot and the fourth pilot;

[0024] determining a timing error matrix by taking the first phase difference average value, the second phase difference average value, the third phase difference average value, and the fourth phase difference average value as elements, the timing error matrix being the phase information.

[0025] Further, the determining the timing error matrix by taking the first phase difference average value, the second phase difference average value, the third phase difference average value, and the fourth phase difference average value as elements includes:

[0026] taking the first phase difference average value as a first row and a first column element of the timing error matrix;

[0027] taking the second phase difference average value as a first row and a second column element of the timing error matrix;

[0028] taking the third phase difference average value as a second row and a first column element of the timing error matrix;

[0029] taking the fourth phase difference average value as a second row and a second column element of the timing error matrix.

[0030] Further, the determining the timing error value and the delay value according to the phase information includes:

[0031] according to a formula

[0032] eτ = -Im[det(S pilot )]

[0033] = -Im[det(S τ ) ] ; wherein e pilot is the timing error value, S p is the timing error matrix, det() is the matrix determinant operator, and Im[] is the imaginary part operator.

[0034] Further, the determining the timing error value and the delay value according to the phase information comprises:

[0035] = -Im[det(S

[0036]

[0037] = -Im[det(S

[0038] Further, the timing error estimation method for dual-polarization quantum key distribution further comprises:

[0039] performing PID feedback control according to the timing error value.

[0040] The timing error estimation method for dual-polarization quantum key distribution in the embodiment can determine the timing error value and the delay value according to the pilot in the signal transmitted by the sending end, and the receiving end can determine the timing error value and the delay value according to the pilot in the received signal, so that the timing error value and the delay value can be accurately determined even if the quantum communication system is weak in signal comparison, and the timing error estimation can be performed. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 FIG. 1 is a schematic diagram of a quantum communication system to which the timing error estimation method for dual-polarization quantum key distribution in the embodiment can be applied;

[0042] Figure 2 FIG. 2 is a schematic diagram of steps of the timing error estimation method for dual-polarization quantum key distribution performed by the sending end in the embodiment;

[0043] Figure 3 FIG. 3 is a schematic diagram of a frequency spectrum of a communication signal transmitted by the sending end in the embodiment after the polarization multiplexed pilot;

[0044] Figure 4 FIG. 4 is a schematic diagram of steps of the timing error estimation method for dual-polarization quantum key distribution performed by the receiving end in the embodiment.

[0045] Figure 5 This is a schematic diagram of the spectrum of the received signal received by the receiving end in the embodiment. Detailed Implementation

[0046] The timing error estimation method for dual-polarization quantum key distribution in this embodiment can be applied to... Figure 1 The quantum communication system shown. (Refer to...) Figure 1 The quantum communication system includes a transmitter, a receiver, and an optical fiber channel. The transmitter needs to send information to the receiver through the optical fiber channel. The information to be sent is mainly presented in the form of quantum communication signals. The content of the information to be sent can be a dual-polarization quantum key, thereby realizing dual-polarization quantum key distribution from the transmitter to the receiver (also known as continuous variable quantum key distribution, CVQKD).

[0047] In this embodiment, the complete timing error estimation method for dual-polarization quantum key distribution includes steps S1A-S3A performed by the transmitter and steps S1B-S4B performed by the receiver.

[0048] Reference Figure 1 The transmitting end includes a laser source and a signal modulation module. The laser source generates a laser beam with a single frequency. This laser beam is input to the signal modulation module. On the one hand, the signal modulation module modulates the communication signal into the laser. On the other hand, the signal modulation module executes steps S1A-S3A.

[0049] In this embodiment, since the signal is carried by a laser, unless otherwise specified, the “communication signal” itself and the laser beam carrying the communication signal can be ignored. Similarly, the “received signal” itself and the laser beam carrying the received signal can also be ignored.

[0050] Reference Figure 2 The timing error estimation method for dual-polarization quantum key distribution, executed by the transmitting end, includes the following steps:

[0051] S1A. Multiplex the first pilot and the third pilot on the spectrum of the first polarization of the communication signal;

[0052] S2A. The second pilot and the fourth pilot are multiplexed on the spectrum of the second polarization of the communication signal;

[0053] S3A. The multiplexed communication signal is transmitted through an optical fiber channel.

[0054] In steps S1A-S2A, the first polarization and the second polarization are two mutually orthogonal directions of polarization, for example, in the present embodiment, the first polarization is X polarization, and the second polarization is Y polarization.

[0055] In the present embodiment, the spectrum of the communication signal after the polarization multiplexing pilot in steps S1A-S2A is shown in Figure 3 Figure 3 The part marked as “communication signal” in

[0056] Referring to Figure 3 , the communication signal before the multiplexing polarization pilot itself has two components of X polarization component and Y polarization component. In step S1A, two pilots, the first pilot (pilot 1) and the third pilot (pilot 3), are multiplexed on the spectrum of the first polarization, i.e., X polarization, and in step S2A, two pilots, the second pilot (pilot 2) and the fourth pilot (pilot 4), are multiplexed on the spectrum of the second polarization, i.e., Y polarization.

[0057] In the present embodiment, referring to Figure 3 , the frequency difference between the first pilot (pilot 1) and the third pilot (pilot 3) and the frequency difference between the second pilot (pilot 2) and the fourth pilot (pilot 4) are equal, both being Δf. In the present embodiment, Δf is equal to one-half of the baud rate of the communication signal. e

[0058] In the present embodiment, referring to Figure 3 , there is a small frequency difference between the first pilot (pilot 1) and the second pilot (pilot 2) and between the third pilot (pilot 3) and the fourth pilot (pilot 4). Specifically, the frequency difference between the first pilot (pilot 1) and the second pilot (pilot 2) and the frequency difference between the third pilot (pilot 3) and the fourth pilot (pilot 4) are equal, both being df. In the present embodiment, df can be a value much smaller than Δf, specifically, 2-3 orders of magnitude smaller than Δf, for example, the value of df can be 10 MHz.

[0059] In step S3A, the multiplexed communication signal, i.e., the signal whose spectrum is shown in Figure 3 , is transmitted by the sending end to the receiving end through the fiber channel.

[0060] Since the dual-polarization laser shown in Figure 3 transmitted in the fiber channel will be affected by physical effects such as state of polarization (SOP) rotation, polarization mode dispersion (PDM), etc., the form of the signal received by the receiving end from the fiber channel is different from the communication signal transmitted by the sending end in terms of spectrum, etc., and therefore in the present embodiment, the signal received by the receiving end from the fiber channel is referred to as the received signal to show the difference between the received signal and the communication signal transmitted by the sending end.​​

[0061] Referring to Figure 1 , the receiving end comprises a signal receiving module, a timing error estimation module and a PID feedback control module.

[0062] In this embodiment, referring to Figure 4 , the timing error estimation method for dual-polarization quantum key distribution performed by the receiving end comprises the following steps:

[0063] S1B. Obtain a received signal;

[0064] S2B. Obtain a first pilot, a second pilot, a third pilot, a fourth pilot, a fifth pilot, a sixth pilot, a seventh pilot and an eighth pilot according to the received signal;

[0065] S3B. Obtain phase information of the first pilot, the second pilot, the third pilot, the fourth pilot, the fifth pilot, the sixth pilot, the seventh pilot and the eighth pilot;

[0066] S4B. Determine a timing error value and a delay value according to the phase information.

[0067] In step S1B, the received signal can be obtained by the signal receiving module.

[0068] In step S2B, due to the influence of physical effects occurring in the optical channel, the received signal received by the receiving end has a spectrum structure as shown in FIG. 2. Referring to Figure 5 , the “communication signal” contained in the received signal is equivalent to the spectrum component of the communication signal before the polarization multiplexed pilot, and the pilot P X1 in it is the same as the spectrum component of the first pilot (pilot 1) in the communication signal after the polarization multiplexed pilot, so it is still called the first pilot P X1 contained in the received signal and is denoted as P X3 ; Similarly, the pilot P X3 is the same as the spectrum component of the third pilot (pilot 3) in the communication signal after the polarization multiplexed pilot, that is, the third pilot P y2 is contained in the received signal; the pilot P y2 is the same as the spectrum component of the second pilot (pilot 2) in the communication signal after the polarization multiplexed pilot, that is, the second pilot P y4 is contained in the received signal; and the pilot P y4 is the same as the spectrum component of the fourth pilot (pilot 4) in the communication signal after the polarization multiplexed pilot, that is, the fourth pilot P X1 is contained in the received signal.

[0069] Referring to Figure 5 , the received signal received by the receiving end also includes a fifth pilot P y1 generated by physical effects during transmission through the optical fiber channely1 , the second pilot P y2 the sixth pilot P X2 , the third pilot P X3 the seventh pilot P y3 , the fourth pilot P y4 the eighth pilot P X4 .

[0070] Referring to Figure 5 , the frequency difference between the sixth pilot P X2 and the eighth pilot P X4 , the frequency difference between the fifth pilot P y1 and the seventh pilot P y3 is also Δf.

[0071] Referring to Figure 5 , in this embodiment, the frequencies of the first pilot P X1 , the second pilot P y2 , the third pilot P X3 , the fourth pilot P y4 , the fifth pilot P y1 , the sixth pilot P X2 , the seventh pilot P y3 and the eighth pilot P X4 are all greater than the frequency of the communication signal before the polarization multiplexed pilot. The frequency of the fifth pilot P y1 is the same as that of the first pilot P X1 , the frequency of the sixth pilot P X2 is the same as that of the second pilot P y2 , the frequency of the seventh pilot P y3 is the same as that of the third pilot P X3 , and the frequency of the eighth pilot P X4 is the same as that of the fourth pilot P y4 .

[0072] In step S3B, the phase information of the first pilot P X1 , the second pilot P y2 , the third pilot P X3 , the fourth pilot P y4 , the fifth pilot P y1 , the sixth pilot P X2 , the seventh pilot P y3 and the eighth pilot P X4 may be obtained by the timing error estimation module. Specifically, the phase information includes the phases of these pilots and the phase difference between two pilots.

[0073] During step S3B, the timing error estimation module can perform an analysis of the first pilot P. X1 Second pilot P y2 Third pilot P X3 Fourth pilot P y4 Fifth pilot P y1 Sixth pilot P X2 Seventh pilot P y3 and the eighth pilot P X4 Down-conversion is performed, which involves moving these pilot signals to the baseband. Then, the timing error estimation module filters the down-converted pilot signals to obtain their respective phase information. Specifically, the timing error estimation module can perform Wiener filtering on the down-converted pilot signals.

[0074] The timing error estimation module obtains the first pilot frequency P by performing filtering. X1 phase θ px1 Second pilot P y2 phase θ py2 Third pilot P X3 phase θ px3 Fourth pilot P y4 phase θ py4 Fifth pilot P y1 phase θ py1 Sixth pilot P X2 phase θ px2 Seventh pilot P y3 phase θ px3 and the eighth pilot P X4 phase θ px4 .

[0075] During step S3B, the timing error estimation module calculates the first pilot P. X1 With the third pilot P X3 phase difference θ px1 -θ px3 and the sixth pilot P X2 With the eighth pilot P X4 phase difference θ px2 -θ px4 And calculate the average of these two phase differences to obtain the first phase difference average value.

[0076] During step S3B, the timing error estimation module calculates the first pilot P. X1 With the seventh pilot P y3 phase difference θ px1 -θ py3 and the sixth pilot P X2 With the fourth pilot P y4 phase difference θ px2 -θpy4 and the average of the two phase differences is calculated to obtain a second phase difference average

[0077] In performing step S3B, the timing error estimation module calculates the phase difference θ y1 - θ X3 between the fifth pilot P py1 and the third pilot P px3 , and the phase difference θ y2 - θ X4 between the second pilot P py2 and the eighth pilot P px4 , and calculates the average of the two phase differences to obtain a third phase difference average

[0078] In performing step S3B, the timing error estimation module calculates the phase difference θ y1 - θ y3 between the fifth pilot P py1 and the seventh pilot P py3 , and the phase difference θ y2 - θ y4 between the second pilot P py2 and the fourth pilot P py4 , and calculates the average of the two phase differences to obtain a fourth phase difference average

[0079] In performing step S3B, the timing error estimation module takes the first phase difference average as the first row first column element, i.e. (1, 1) term, takes the second phase difference average as the first row second column element, i.e. (1, 2) term, takes the third phase difference average as the second row first column element, i.e. (2, 1) term, and takes the fourth phase difference average as the second row second column element, i.e. (2, 2) term, to form a timing error matrix S pilot . That is, in this embodiment, the timing error matrix S pilo t can be represented as

[0080]

[0081] The timing error matrix S pilot contains the phase difference information between each pilot, which can be used as the phase information obtained by the timing error estimation module in performing step S3B.

[0082] In step S4B, the timing error estimation module can calculate the timing error e

[0083] according to the formulaτ = -Im[det(S pilot

[0084] The calculation is performed to obtain the timing error value e τ . Wherein, det() is the operator of taking the determinant of a matrix, and Im[] is the operator of taking the imaginary part of a complex number.

[0085] In step S4B, the timing error estimation module can calculate according to the formula

[0086]

[0087] The calculation is performed to obtain the delay value τ. Wherein, det() is the operator of taking the determinant of a matrix, angle[] is the operator of taking the angle of a complex number, and Δf is the frequency difference between the first pilot P X1 and the third pilot P X3 , and is also the frequency difference between the second pilot P y2 and the fourth pilot P y4 , the frequency difference between the sixth pilot P X2 and the eighth pilot P X4 , and the frequency difference between the fifth pilot P y1 and the seventh pilot P y3 .

[0088] By performing steps S1A-S3A, the signal sent by the sending end contains pilots that can determine the timing error value e τ and the delay value τ, and by performing steps S1B-S4B, the receiving end can determine the timing error value e τ and the delay value τ according to the pilots contained in the received signal; even if applied to a quantum communication system with weak signal comparison, the timing error value and the delay value can be accurately determined, so that timing error estimation can be performed. In the case of high frequency of the pilot, the performance of timing error estimation is better.

[0089] In this embodiment, the receiving end can perform the following steps on the basis of performing steps S1B-S4B:

[0090] S5B. Perform PID feedback control according to the timing error value.

[0091] Referring to Figure 1 , after the timing error estimation module obtains the timing error value e τ by performing steps S1B-S4B, the timing error value e τ can be sent to the PID feedback control module, and the PID feedback control module can generate a feedback signal according to the timing error value e τ , and adjust the signal receiving module according to the feedback signal, so as to achieve the effect of reducing or eliminating the timing error.​

[0092] The timing error estimation method for dual-polarization quantum key distribution in the embodiments can be implemented by writing a computer program for executing the timing error estimation method for dual-polarization quantum key distribution in the embodiments, writing the computer program into a computer device or a storage medium, and executing the timing error estimation method for dual-polarization quantum key distribution in the embodiments when the computer program is read out and run, so as to achieve the same technical effects as the timing error estimation method for dual-polarization quantum key distribution in the embodiments.

[0093] It should be noted that, unless otherwise specified, when a certain feature is said to be "fixed" or "connected" to another feature, it can be directly fixed or connected to the other feature, or indirectly fixed or connected to the other feature. In addition, the up, down, left, right and the like used in the present disclosure are only relative to the relative positional relationship of the components of the present disclosure in the drawings. The singular forms "a" and "the" used in the present disclosure are also intended to include the plural forms, unless the context clearly indicates otherwise. In addition, unless otherwise defined, all technical and scientific terms used in the embodiments have the same meaning as generally understood by those skilled in the art. The terms used in the embodiments are only used to describe the specific embodiments, and are not intended to limit the present application. The term "and / or" used in the embodiments includes any combination of one or more related listed items.

[0094] It should be understood that although the terms first, second, third, etc. can be used in the present disclosure to describe various elements, these elements should not be limited to these terms. These terms are only used to distinguish one type of element from another type of element. For example, without departing from the scope of the present disclosure, the first element can also be referred to as the second element, and similarly, the second element can also be referred to as the first element. The use of any and all examples or exemplary language (e.g., "for example", "as such", etc.) provided in the present embodiments is only intended to better illustrate the embodiments of the present application, and unless otherwise required, does not impose any limitation on the scope of the present application.

[0095] It should be appreciated that embodiments of the present application can be implemented or realized in a computer system having computer hardware, a combination of computer hardware and software, or by computer instructions stored on a non-transitory computer-readable medium, which if executed by a computer, would cause the computer to perform a method described herein. The methods can be implemented using standard programming techniques - including the configuration of a non-transitory computer-readable storage medium with computer program code in accordance with the teachings of the present application. Each program can be implemented in a high level procedural or object oriented programming language to be executed by a computer. However, if desired, the programs can be implemented in assembly or machine language. In any case, the language can be a compiled or interpreted language. Furthermore, the programs can be stored on a computer program product in the form of a non-transitory computer-readable storage medium, which is distributed so as to be read by a suitable computer. Such a medium can take many forms, for example it can be a magnetic or optical disk, a magnetic tape, or a magnetic or optical card. It is therefore to be understood that the present application can be carried out by computer software implemented for this purpose. The application includes a computer program tangibly embodied on a non-transitory computer-readable storage medium and a computer.

[0096] Furthermore, the operations of the processes described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The processes described herein (or variations and / or combinations thereof) can be implemented under the control of one or more computer systems configured with executable instructions (e.g., computer program code), which can be stored in computer program products, i.e., any medium readable and / or writable by a machine, including volatile memory, non-volatile memory, removable storage media, etc. The computer program products can be distributed over network coupled computer systems so that the computer program code is stored and executed in a distributed fashion.

[0097] Further, the methods can be implemented in any suitable type of computing platform operably connected to any suitable type of computing platform, including but not limited to a personal computer, a mini-computer, a mainframe, a workstation, a network or distributed computing environment, a separate or integrated computer platform, or in communication with a charged particle tool or other imaging device, etc. Aspects of the present application can be implemented in machine readable code stored on a non-transitory storage medium or device, whether removable or integrated to the computing platform, such as a hard disk, an optical read and / or write storage medium, RAM, ROM, etc., such that it is readable by a programmable computer and, when the storage medium or device is read by the computer, is operable to configure and operate the computer to perform the processes described herein. Furthermore, the machine readable code, or portions thereof, can be transmitted over a wired or wireless network. The present application encompasses these and other different types of non-transitory computer readable storage media when the instructions or programs incorporating the above steps are implemented in conjunction with a microprocessor or other data processor. The present application also encompasses the computer itself when programmed in accordance with the methods and techniques of the present application.

[0098] A computer program can be applied to input data to perform the functions of the present embodiments to transform the input data to generate output data that is stored to non-volatile memory. The output information can also be applied to one or more output devices such as a display. In a preferred embodiment of the present application, the transformed data represents a physical and tangible object, including a particular visual depiction of a physical and tangible object produced on a display.

[0099] The above merely preferred embodiments of the present application and are not intended to limit the present application. The present application can be carried out in other ways than those specifically set forth herein without departing from the essential characteristics of the application. The present embodiments are therefore to be construed in all aspects as illustrative and not restrictive.

Claims

1. A timing error estimation method for dual-polarization quantum key distribution, applied to a sending end, characterized in that, The timing error estimation method for dual-polarization quantum key distribution comprises: multiplexing a first pilot and a third pilot on a spectrum of a first polarization of a communication signal; multiplexing a second pilot and a fourth pilot on a spectrum of a second polarization of the communication signal; transmitting the multiplexed communication signal through a fiber channel; a frequency difference between the first pilot and the third pilot and a frequency difference between the second pilot and the fourth pilot are both equal to a one-half baud rate of the communication signal; a frequency difference between the first pilot and the second pilot and a frequency difference between the second pilot and the fourth pilot are both equal and less than the one-half baud rate of the communication signal.

2. A timing error estimation method for dual-polarization quantum key distribution, applied to a receiving end, characterized in that, The timing error estimation method for dual-polarization quantum key distribution comprises: obtaining a received signal; the received signal is obtained by transmitting the communication signal through a fiber channel in the timing error estimation method for dual-polarization quantum key distribution of claim 1, and the communication signal is multiplexed with a first pilot and a third pilot on a spectrum of a first polarization and multiplexed with a second pilot and a fourth pilot on a spectrum of a second polarization before being transmitted; obtaining the first pilot, the second pilot, the third pilot, the fourth pilot, a fifth pilot, a sixth pilot, a seventh pilot and an eighth pilot according to the received signal; wherein the fifth pilot is generated by a physical effect of transmitting the first pilot through a fiber channel, the sixth pilot is generated by a physical effect of transmitting the second pilot through a fiber channel, the seventh pilot is generated by a physical effect of transmitting the third pilot through a fiber channel, and the eighth pilot is generated by a physical effect of transmitting the fourth pilot through a fiber channel; the frequency of the fifth pilot is the same as the frequency of the first pilot, the frequency of the sixth pilot is the same as the frequency of the second pilot, the frequency of the seventh pilot is the same as the frequency of the third pilot, and the frequency of the eighth pilot is the same as the frequency of the fourth pilot; obtaining phase information of the first pilot, the second pilot, the third pilot, the fourth pilot, the fifth pilot, the sixth pilot, the seventh pilot and the eighth pilot; determining a timing error value and a delay value according to the phase information.

3. The timing error estimation method for dual polarization quantum key distribution according to claim 2, characterized in that, The method for obtaining the phase information of the first pilot, the second pilot, the third pilot, the fourth pilot, the fifth pilot, the sixth pilot, the seventh pilot and the eighth pilot comprises: down-converting the first pilot, the second pilot, the third pilot, the fourth pilot, the fifth pilot, the sixth pilot, the seventh pilot and the eighth pilot; filtering the down-converted pilots to obtain the phase information.

4. The timing error estimation method for dual polarization quantum key distribution according to claim 3, characterized in that, The method for filtering the down-converted pilots to obtain the phase information comprises: Wiener filtering the down-converted pilots to obtain the phase of each of the first pilot, the second pilot, the third pilot, the fourth pilot, the fifth pilot, the sixth pilot, the seventh pilot and the eighth pilot. acquiring a first phase difference average value; the first phase difference average value is an average value of a phase difference between the first pilot and the third pilot and a phase difference between the sixth pilot and the eighth pilot; acquiring a second phase difference average value; the second phase difference average value is an average value of a phase difference between the first pilot and the seventh pilot and a phase difference between the sixth pilot and the fourth pilot; acquiring a third phase difference average value; the third phase difference average value is an average value of a phase difference between the fifth pilot and the third pilot and a phase difference between the second pilot and the eighth pilot; acquiring a fourth phase difference average value; the fourth phase difference average value is an average value of a phase difference between the fifth pilot and the seventh pilot and a phase difference between the second pilot and the fourth pilot; determining a timing error matrix by taking the first phase difference average value, the second phase difference average value, the third phase difference average value and the fourth phase difference average value as elements; the timing error matrix is the phase information.

5. The timing error estimation method for dual polarization quantum key distribution according to claim 4, characterized in that, The determining a timing error matrix by taking the first phase difference average value, the second phase difference average value, the third phase difference average value and the fourth phase difference average value as elements comprises: taking the first phase difference average value as a first row first column element of the timing error matrix; taking the second phase difference average value as a first row second column element of the timing error matrix; taking the third phase difference average value as a second row first column element of the timing error matrix; taking the fourth phase difference average value as a second row second column element of the timing error matrix.

6. The timing error estimation method for dual-polarization quantum key distribution according to claim 4 or 5, characterized in that, The determining a timing error value and a delay value according to the phase information comprises: according to a formula performing the calculation; wherein is the timing error value, is the timing error matrix, is a take matrix determinant operator, is a take imaginary part operator.

7. The timing error estimation method for dual-polarization quantum key distribution according to claim 4 or 5, characterized in that, The determining a timing error value and a delay value according to the phase information comprises: according to a formula performing the calculation; wherein is the delay value, is the timing error matrix, is the determinant operator, is the complex angle operator, is the frequency difference between the first pilot and the third pilot.

8. The timing error estimation method for dual-polarization quantum key distribution according to any one of claims 2-5, characterized in that, The timing error estimation method for dual polarization quantum key distribution further comprises: performing PID feedback control according to the timing error value.

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