Continuous variable quantum repeater communication protocol and design method thereof

Abstract

The invention discloses a continuous variable quantum repeater communication protocol and a design method thereof, an error correction module is used to carry out error correction on a pure loss link between a sender Alice and a receiver Bob, two adjacent loss links are connected through a quantum repeater node, and one mode in a dual-mode compressed Gaussian state is transmitted from the sender Alice to the receiver Bob. According to the module, quantum teleportation and a noiseless linear amplifier are combined, and the communication performance is improved by introducing thermal noise and a multiplexing method according to the improved scheme. The CVQR protocol has significant advantages in the aspect of key rate under collective attacks, and the proposed CVQR protocol paves a way for implementation of long-distance CV-QKD.

Description

Technical Field

[0001] The present invention belongs to the technical field of quantum communication, and in particular relates to a continuous variable quantum repeater communication protocol and a design method thereof. Background Art

[0002] As people pay more attention to efficient and secure information transmission, quantum secure communication is found to be a promising solution. As an important component of secure quantum communication, quantum key distribution (QKD) theoretically achieves unconditional security and has become one of the research hotspots in the field of quantum information.

[0003] Continuous variable quantum key distribution (CV-QKD) was first proposed in 1999. Although it appeared later than discrete variable quantum key distribution, CV-QKD has many advantages, including high key rate, low cost, strong anti-interference ability, and adaptability to integration with existing traditional fiber networks. This can reduce deployment costs and demonstrate its potential for large-scale practical applications. However, the communication distance of QKD is severely limited by the exponential loss of optical fiber, which is why CV-QKD currently only shows advantages over medium and short distances. Continuous variable quantum repeater (CVQR) is an important means to overcome the distance limitation of continuous variable quantum communication and an important component for achieving high-speed quantum communication. Since 2008, researchers have begun to explore the implementation and optimization of entanglement distillation and exchange components in CVQR, and enhance individual components. In addition to improving the key rate and communication distance of CV-QKD, efforts have recently been made in the transmission of discrete variable quantum states to improve the performance of quantum sensor networks and other applications.

[0004] Current designs of CVQR rely heavily on distilling entangled quantum states using noiseless linear amplifiers (NLA). When the average number of photons is small, NLA can make the transmitted state approximate the target state well using probabilistic quantum scissors. However, using NLA usually results in a low success probability and introduces truncation noise, which degrades the transmission performance. How to minimize the impact of NLA truncation noise while maintaining a reasonable success probability has not yet been addressed. Introducing additional noise may help. The use of noise processing can be viewed as a distillation scheme that can be used to improve the key rate.

[0005] Continuous variable quantum repeater (CVQR) plays a key role in continuous variable quantum key distribution (CV-QKD). It can greatly extend the communication distance of CV-QKD. Currently, most CVQR designs rely on entanglement distillation using noiseless linear amplifiers. However, practical noiseless linear amplifiers may degrade communication performance and have low success rates due to truncation noise generated during the amplification process. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a continuous variable quantum repeater communication protocol and a design method thereof, which solves the problem of low success probability of the scheme after introducing a noise-free linear amplifier to optimize performance in the prior art.

[0007] The present invention adopts the following technical solutions to solve the above technical problems:

[0008] A continuous variable quantum repeater communication protocol uses an error correction module to correct the pure loss link between the sender Alice and the receiver Bob. Two adjacent lossy links are connected by quantum repeater nodes, and one mode in the two-mode compressed Gaussian state is transmitted from the sender Alice to the receiver Bob.

[0009] The error correction module includes two optical switches, between which a dual-mode compressed Gaussian state is multiplexed on a spectrum or a space mode. , Each mode "2" of the quantum state passes through the loss channel and is corrected by a noise-free linear amplifier, and each mode "1" is stored in the quantum memory; two optical switches scan all the memories and find path to success.

[0010] The teleportation process of the error correction module is as follows:

[0011] The input optical switch releases the successful mode "1" and One of the modes is measured with double zero difference, and the measurement result is Perform displacement operation on the successful mode "2" released by the output optical switch , and then add thermal noise to represent the thermal model The output state of the error correction module is obtained by coupling with mode "2" at the beam splitter. .

[0012] All error correction modules perform the teleportation process to complete the entire quantum repeater protocol and obtain the final state.

[0013] The design method of the continuous variable quantum repeater communication protocol includes the following steps:

[0014] Step 1: One mode of the dual-mode resource state in the initial error correction module is multiplexed, and at the same time, it passes through the entanglement link and is purified using NLA, and the mode successfully selected by the quantum optical switch is stored in the quantum memory;

[0015] Step 2: For the dual-mode resource state in which one mode is successfully purified, the other mode is released by the quantum optical switch at the input end, and a double homodyne measurement is performed with the input mode, and the obtained result is transmitted to the receiver through the classical channel;

[0016] Step 3: Based on the double-homodyne measurement results, the receiver performs displacement transformation on the successfully purified mode of the resource state to complete the teleportation process;

[0017] Step 4: The shift-transformed mode is coupled with the thermal mode at the beam splitter to introduce thermal noise into the quantum state, thereby obtaining the output state of the initial error correction module;

[0018] Step 5: Use the output state of the initial error correction module as the input state of the next error correction module, repeat steps 2 to 4 according to the required number of error correction modules, and obtain the result state of the entire continuous variable quantum repeater scheme.

[0019] After obtaining the result state of the entire continuous variable quantum repeater scheme, the performance of the repeater scheme is verified by calculating the result state covariance matrix.

[0020] The performance parameters include the probability of success under collective attack and reverse coordination key rate .

[0021] Through performance calculation, the final performance of the repeater solution is quantified. The error correction module, the success probability is calculated using the following formula:

[0022]

[0023] in , , , , , , , denote the success probabilities of the optical switch, quantum memory, loss channel, noise-free linear amplifier, and beam splitter when thermal noise is introduced, respectively. and Set to a fixed value, is the multiplexing number, is the number of quantum nodes.

[0024] Before quantifying the final performance, determine the values ​​of all relevant parameters, assume some basic parameters as fixed values, and then optimize and analyze the remaining parameters to determine the optimal reuse number. , noise-free linear amplifier gain and thermal noise .

[0025] For non-ideal input states, when analyzing the impact of the loss degree of a certain input state on other parameter values, the efficiency parameter is also considered. and external noise ; When loss is the main noise source, external noise Modeled as a certain proportional relationship.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. This module combines quantum teleportation and noiseless linear amplifier. The improved scheme improves communication performance by introducing thermal noise and multiplexing methods. Through analysis, the optimal variable parameter values ​​are given.

[0028] 2. This invention proposes an improved CVQR protocol using multi-mode multiplexing and thermal noise assistance. The results show that at 100 km, the success rate of this protocol is 0.4011, while the success rate of the original protocol is 0.1177; the key rate of this protocol under collective attack is 1.3659 bit / pulse, while the key rate of the original protocol at 500 km is 0.1471 bit / pulse. .

[0029] 3. The present invention has significant advantages in terms of key rate under collective attacks, and the proposed CVQR protocol paves the way for the realization of long-distance CV-QKD. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of the optimization scheme for continuous variable quantum repeaters;

[0031] Figure 2 This is a schematic diagram of the original error correction module;

[0032] Figure 3 This is a schematic diagram of the error correction module of this optimization solution;

[0033] Figure 4 The performance comparison at different communication distances before and after the scheme improvement is shown;

[0034] Figure 5 is the relationship between the success probability and NLA gain under different multiplexing numbers;

[0035] Figure 6 The relationship between NLA gain and optimal thermal noise under input states with different loss levels;

[0036] Figure 7 is the relationship between the ideal input state key rate and the NLA gain;

[0037] Figure 8 Comparison of success probability at different communication distances before and after the scheme improvement;

[0038] Fig. 9 Comparison of key rates under different communication distances before and after the scheme improvement. DETAILED DESCRIPTION

[0039] The structure and working process of the present invention will be further described below in conjunction with the accompanying drawings.

[0040] A continuous variable quantum repeater communication protocol uses an error correction module to correct the pure loss link between the sender Alice and the receiver Bob. Two adjacent lossy links are connected by quantum repeater nodes, and one mode in the two-mode compressed Gaussian state is transmitted from the sender Alice to the receiver Bob.

[0041] The error correction module includes two optical switches, between which a dual-mode compressed Gaussian state is multiplexed on a spectrum or a space mode. , Each mode "2" of the quantum state passes through the loss channel and is corrected by a noise-free linear amplifier, and each mode "1" is stored in the quantum memory; two optical switches scan all the memories and find path to success.

[0042] The design method of the above-mentioned continuous variable quantum repeater communication protocol includes the following steps:

[0043] Step 1: One mode of the dual-mode resource state in the initial error correction module is multiplexed, and at the same time, it passes through the entanglement link and is purified using NLA, and the mode successfully selected by the quantum optical switch is stored in the quantum memory;

[0044] Step 2: For the dual-mode resource state in which one mode is successfully purified, the other mode is released by the quantum optical switch at the input end, and a double homodyne measurement is performed with the input mode, and the obtained result is transmitted to the receiver through the classical channel;

[0045] Step 3: Based on the double-homodyne measurement results, the receiver performs displacement transformation on the successfully purified mode of the resource state to complete the teleportation process;

[0046] Step 4: The shift-transformed mode is coupled with the thermal mode at the beam splitter to introduce thermal noise into the quantum state, thereby obtaining the output state of the initial error correction module;

[0047] Step 5: Use the output state of the initial error correction module as the input state of the next error correction module, repeat steps 2 to 4 according to the required number of error correction modules, and obtain the result state of the entire continuous variable quantum repeater scheme.

[0048] Specific embodiments, such as Figures 1 to 9 As shown,

[0049] The scheme design of the continuous variable quantum repeater optimization scheme designed by the present invention is as follows Figure 1 , where the optimized error correction module is designed as follows Figure 3 , the original error correction module is as follows Figure 2For the design of the continuous variable quantum repeater optimization scheme, each error correction module consists of a teleportation process and a beam splitter that introduces thermal noise.

[0050] 1. Solution design

[0051] The continuous variable quantum repeater (CVQR) scheme proposed in the present invention is as follows Figure 1 To extend the effective communication distance, use Error Correction Module To compare the relationship between Alice and Bob CVQR node, namely rNode , connecting two adjacent lossy links. Alice wants to transmit one mode of the two-mode compressed Gaussian state (TMSV) to Bob.

[0052] In this improved solution, an error correction module is Figure 3 As shown, the original error correction module is as follows Figure 2 NLA is used to correct the Gaussian noise introduced by a pure lossy link. For the sake of discussion, both error correction modules are considered However, NLA will bring truncation noise, which is unfavorable to the key rate in the communication scheme, and its uncertainty will lead to a low success probability. To overcome these shortcomings, this scheme uses multiplexing method and thermal noise to improve Figure 2 The error correction module in .

[0053] With multiplexing, the probability of success of a solution can be optimized. Figure 3 In the TMSV state Multiplexing on spectral or spatial modes. Each mode "2" of passes through the loss channel and is corrected by NLA, while each mode "1" is stored in the quantum memory. Since the truncation noise caused by a quantum scissors is much stronger than the channel noise, it is only necessary to analyze the ability of thermal noise to suppress truncation noise. If an NLA operation is successful, the successful mode is stored and the signal is sent to the previous node. Figure 3 The two optical switches in the The rest of the teleportation process is similar to Figure 2 Similar: The left optical switch will release the success mode "1" and A double homodyne measurement is performed on one mode in the measurement. Perform displacement operation on the successful mode "2" released by the right optical switch .

[0054] The final step is to add thermal noise (using analog Represented), by the two-mode entangled state The module F is measured to obtain the module The addition of thermal noise can suppress the truncation noise of NLA and thus improve the key rate of the scheme. and mode "2" are coupled at the beam splitter, and then the output state of the error correction module is obtained .

[0055] Each error correction module The same steps are followed. By repeating the above process times (such as Figure 1 As shown), the entire CVQR scheme is completed and the final state is obtained The performance discussed in this paper is the success probability under collective attack and reverse coordination key rate For non-ideal cases, mixed TMSV input states, inefficient optical switches, and inefficient quantum memories are considered. When the distance of each lossy link is 100 km, the performance improvement of the improved scheme compared with the original model is as follows Figure 4 The performance of the optimized solution is significantly better. and It is close to 0 at 300km and 500km respectively, and the improved scheme still performs well.

[0056] 2. Calculation of the result state covariance matrix

[0057] Assume the input state and TMSV state is a pure two-mode squeezed state, expressed as , ,in and are the compression strengths corresponding to the TMSV state. Figure 3 As shown, the symbols of the scheme are: Environmental model of lossy link ; NLA gain ; Teleportation gain ; Double zero difference measurement results ; Transmission efficiency of pure lossy channel ; The length of each lossy link ; Variance of thermal noise introduced ; Transmission rate of beam splitter . The covariance matrix can characterize a Gaussian state, such as the TMSV state, and further operations can be easily represented based on the initial covariance matrix. The calculation process of the key rate and success probability under collective attack is represented by the transformation of the covariance matrix. It should be noted that NLA is a non-Gaussian operation, and the impact of the equivalent calculation process on the covariance matrix will be discussed at the end of this section. Considering the pure TMSV state, The covariance matrix of is:

[0058]

[0059] in, , , , is the compression parameter, is the identity matrix, and is the Pauli matrix . The covariance matrix of use replace The latter form is consistent.

[0060] An actual input TMSV state Based on the possible internal losses and external noise, The covariance matrix of becomes:

[0061]

[0062] in,

[0063] , , , compression parameters It will be multiplied by an efficiency factor ( ),Right now , is the amount of internal noise.

[0064] TMSV state After a pure loss channel and NLA with single quantum scissors, the resulting state is:

[0065]

[0066] Environmental Model Find the trace, then Density operator of the trace state for

[0067]

[0068] The covariance matrix of is:

[0069]

[0070] in

[0071]

[0072] Some scholars have proposed a method to simulate Gaussian channels using teleportation process. The Gaussian channel simulation method can be used to simplify the calculation of the output state of the teleportation process. The transmission parameters of the simulated channel are and channel noise for:

[0073] ,

[0074] Resource state entanglement cannot be lower than the Choi state through the Gaussian channel ( ) after the entanglement degree, that is, it needs to satisfy .

[0075] The covariance matrix of the output state can be expressed as:

[0076]

[0077] in is the identity matrix, represents the zero matrix, , .

[0078] Covariance matrix of the output state of the teleportation process for:

[0079]

[0080] and the variance is Thermal mold At a transmittance of The thermal noise is coupled to the beam splitter. Error correction module The covariance matrix of the output state is:

[0081]

[0082] in, , , , .

[0083] By transforming the teleportation output state covariance matrix accordingly, we can get The covariance matrix of the output state . The output is and repeat the above calculation process. The output state of is represented as When having When there are quantum repeater nodes, It can represent the covariance matrix of the corresponding output state.

[0084] 3. Performance calculation

[0085] Based on the above calculation of the output state covariance matrix, the present invention discusses Performance comparison between the node quantum repeater optimization scheme and the original model (key rate under collective attack and the probability of success ).

[0086] Assume that the collective attack is performed by the eavesdropper Eve. During the reverse coordination, the key rate of this scheme is ,in represents the mutual information between Alice and Bob, Indicates the information that Eve can obtain. In order to distinguish the key rates of different schemes, the key rate of the original scheme is expressed as . and The calculation is performed according to the following procedure.

[0087] For Gaussian distributed continuous variables , , entropy is , conditional entropy ,in yes The variance of It is measured The quantum state after The variance of is a constant. The variance of a single mode is the value on the diagonal of the corresponding covariance matrix. Therefore and It can be expressed as:

[0088]

[0089]

[0090] The amount of information Eve obtains is , The information Eve obtains is equivalent to the purification of Alice and Bob's system, so For the optimized (or original) solution, Bob obtains (or ), the system AECF (or AE) is pure, so we have . and There are the following forms:

[0091]

[0092] in, , , and the VonNeuman entropy of the hot state . Represents the covariance matrix of the final output state of the system The symplectic eigenvalues ​​of Represents the system state covariance matrix after homodyne measurement of Bob (or ). These symplectic eigenvalues ​​are:

[0093]

[0094]

[0095]

[0096] in

[0097]

[0098]

[0099] In order to get , we must solve a cubic equation ,in From the covariance matrix The determinant of and its submatrices are given as:

[0100]

[0101] in

[0102]

[0103]

[0104]

[0105] We can use the determinant express:

[0106]

[0107]

[0108]

[0109] After simplification, we have:

[0110]

[0111] Observed ,therefore yes A root of . By solving We can find two more roots . It can be expressed as:

[0112]

[0113] After obtaining all the symplectic eigenvalues, after substituting the values ​​of the covariance matrix items and The value of can be solved.

[0114] Due to the non-Gaussian nature of NLA, using Gaussian process calculation will overestimate the information obtained by Eve. That is, the key rate will be lower than the actual value and lead to negative key rate. In order to make the key rate comparison between this scheme and the original model more natural, when calculating the key rate and A tuning parameter was added To offset Eve's overestimation of information, , .

[0115] The success probability of the plan is Figure 2 The product of the probabilities of the components in . Considering more practical situations, inefficient optical switches and inefficient quantum memories are discussed here. They will affect the final success probability.

[0116] set up , , , , They represent the success probabilities of optical switch, quantum memory, loss channel, NLA, and beam splitter when thermal noise is introduced, respectively. is the multiplexing number, is the number of quantum nodes. For the multiplexing part of an EC module in the scheme, once one or more paths are successful, the related two modules will be stored in two memories. The success probability of a multiplexing path is , then the success probability of the multiplexing part in an error correction module is To further perform the operation, the two optical switches will select a successful path and release the corresponding modules in the two memories. The success probability of this process is .

[0117] have The NLA operator of quantum scissors is , where the truncation operator , and the gain operator Acting on the quantum state .

[0118] When NLA is applied to quantum states When , the action process can be expressed as:

[0119]

[0120] When , the error correction probability of NLA is In order to facilitate further analysis, , to explain when When underestimated, the success probability of this solution is still advantageous.

[0121] Therefore, for The success probability of this repeater scheme with error correction modules is

[0122]

[0123] in , , , and Considering the two inefficient memories in the quantum teleportation process, the success probability of the original model is

[0124]

[0125] 4. Results and Discussion

[0126] In order to quantify the final performance of the scheme before and after optimization, all relevant parameter values ​​need to be determined. Some basic parameters are assumed to be fixed for further discussion. In order to better improve the performance of the scheme, the remaining parameters can be optimized with the help of data analysis. The optimal reuse number is determined by analyzing different situations. 、NLA gain and thermal noise , to improve the performance of the scheme. For non-ideal input states, the efficiency parameter and external noise When studying the effect of the loss level of a certain input state on other parameter values, we should also consider and When losses are the dominant noise source, Modeled as The following discussion assumes that For inefficient optical switches and memories, the efficiency parameter Set to 0.9, Set to 0.99. More basic parameter settings are described below.

[0127] Compression strength for input state (or resource state) (or )have (or ), where the compression parameter . Teleportation Gain Channel transmittance , where the length of each lossy link is km, fiber loss rate of the channel dB / km. Adjustment parameters Set to 3, the variance of the hot state is set to 60. The transmittance of the beam splitter that introduces thermal noise is .

[0128] First, in order to determine the optimal reuse number , Figure 5 Researched or The relationship between NLA gain and success probability in the scheme. Obviously, for the same NLA gain, The larger the value, the higher the probability of success. However, considering the resource cost, it is hoped that Combining these two considerations, Here it is set to 10. Then we analyze Optimal thermal noise at , so that the key rate is maximized.

[0129] When the efficiency parameter of the input state or When , the optimal thermal noise value corresponding to different NLA gains in this scheme is as follows Figure 6 As shown in Figure 2, the greater the input state loss, the more thermal noise is required to obtain the maximum key rate. When , under the corresponding NLA gain, the maximum key rate of the scheme before and after improvement is as follows: Figure 7 As shown in Figure 2, it can be seen that when the NLA gain value is increased, the optimal key rate of this scheme changes little (blue solid line). In addition, a very small NLA gain will significantly increase the success probability, as shown in Figure 2. Figure 5 shown.

[0130] According to the above analysis and Figure 5 , in order to obtain a higher success probability, the optimal NLA gain Should be less than In order to compare the final performance of the schemes before and after optimization, the NLA gain is set to Then MATLAB is used to calculate the optimal thermal noise value that maximizes the key rate in this scheme: dB. When thermal noise is introduced, the transmittance of the beam splitter is After determining all basic parameters and optimal parameter settings, Figure 8 and Fig. 9 The performance comparison of the schemes before and after optimization is discussed.

[0131] when When The performance of the CV-QKD scheme with 1 quantum repeater node has been discussed. In addition, the comparison of the success rate and key rate of the scheme under collective attack before and after optimization is shown in Figure 8 , as shown in Figure 9. The distance of each lossy link is 100 km. The success probability of the CVQR scheme based on the original error correction module at 300 km is close to 0, while the success probability of the CVQR scheme is still of practical significance. Fig. 9 It can be seen that the key rate of the original model at 500km is very low. At the same distance, the key rate of the improved scheme is still very high, which is bits / pulse. Compared with the previous scheme, the proposed scheme has a significant advantage in the key rate under collective attacks at all communication distances.

Claims

1. A continuous variable quantum repeater communication protocol, characterized in that: The error correction module is used to correct the pure lossy link between the sender Alice and the receiver Bob. Two adjacent lossy links are connected by quantum repeater nodes, and one mode in the two-mode compressed Gaussian state is transmitted from the sender Alice to the receiver Bob.

2. The continuous variable quantum repeater communication protocol according to claim 1, characterized in that: The error correction module includes two optical switches, between which a dual-mode compressed Gaussian state is multiplexed on a spectrum or a space mode. , Each mode "2" of the quantum state passes through the loss channel and is corrected by a noise-free linear amplifier, and each mode "1" is stored in a quantum memory; two optical switches scan all memories and find path to success.

3. The continuous variable quantum repeater communication protocol according to claim 2, characterized in that: The teleportation process of the error correction module is as follows: The input optical switch releases successfully mode "1" and One of the modes is measured with double zero difference, and the measurement result is Perform displacement operation on the successful mode "2" released by the output optical switch , and then add thermal noise to represent the thermal model The output state of the error correction module is obtained by coupling with mode "2" at the beam splitter. .

4. The continuous variable quantum repeater communication protocol according to claim 3, characterized in that: All error correction modules perform the teleportation process to complete the entire quantum repeater protocol and obtain the final state.

5. A design method for a continuous variable quantum repeater communication protocol, characterized in that: The steps include: Step 1: One mode of the dual-mode resource state in the initial error correction module is multiplexed, and at the same time, it passes through the entanglement link and is purified using NLA, and the mode successfully selected by the quantum optical switch is stored in the quantum memory; Step 2: For the dual-mode resource state in which one mode is successfully purified, the other mode is released by the quantum optical switch at the input end, and a double homodyne measurement is performed with the input mode, and the obtained result is transmitted to the receiver through the classical channel; Step 3: Based on the double-homodyne measurement results, the receiver performs displacement transformation on the successfully purified mode of the resource state to complete the teleportation process; Step 4: The shift-transformed mode is coupled with the thermal mode at the beam splitter to introduce thermal noise into the quantum state, thereby obtaining the output state of the initial error correction module; Step 5: Use the output state of the initial error correction module as the input state of the next error correction module, repeat steps 2 to 4 according to the required number of error correction modules, and obtain the result state of the entire continuous variable quantum repeater scheme.

6. The design method of the continuous variable quantum repeater communication protocol according to claim 5, characterized in that: After obtaining the result state of the entire continuous variable quantum repeater scheme, the performance of the repeater scheme is verified by calculating the result state covariance matrix and further calculations based on the covariance matrix.

7. The design method of the continuous variable quantum repeater communication protocol according to claim 6, characterized in that: The performance parameters include the probability of success under collective attack and reverse coordination key rate .

8. The design method of the continuous variable quantum repeater communication protocol according to claim 7, characterized in that: Through performance calculation, the final performance of the repeater protocol is quantified. The success probability of the repeater protocol with 1 error correction module is calculated using the following formula: in , , , , , , , denote the success probabilities of the optical switch, quantum memory, loss channel, noise-free linear amplifier, and beam splitter when thermal noise is introduced, respectively. is the transmission efficiency of the lossy channel, and Set to a fixed value, is the multiplexing number, is the number of quantum nodes.

9. The design method of the continuous variable quantum repeater communication protocol according to claim 8, characterized in that: Before quantifying the final performance, determine the values ​​of all relevant parameters, assume some basic parameters as fixed values, and then optimize and analyze the remaining parameters to determine the optimal reuse number. , noise-free linear amplifier gain and thermal noise .

10. The design method of the continuous variable quantum repeater communication protocol according to claim 9, characterized in that: For non-ideal input states, when analyzing the impact of the loss degree of a certain input state on other parameter values, the efficiency parameter is also considered. and external noise ; When losses are the dominant noise source, external noise Modeled as a certain proportional relationship.

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