Source device independent quantum key distribution and network method, device and system

Abstract

The invention discloses a source device independent quantum key distribution method, device and system and a network thereof, and belongs to the technical field of quantum key distribution. In order to solve the problem that an existing quantum key distribution protocol depends on a source end security hypothesis and is difficult to defend unknown source side attacks, the invention provides a source equipment-independent quantum key distribution protocol. Through the physical characteristics of the non-classical quantum light source and a pairing method after measurement, the security hypothesis of source end equipment is removed, known and unknown source side attacks can be effectively resisted, and the quantum advantages in the aspects of security and performance expression compared with a classical laser source are realized. The invention further provides a method for directly expanding the point-to-point protocol to the multi-user quantum key distribution network, compared with an existing quantum network based on an entangled photon source, the complexity of an experiment system and the requirement for equipment are reduced, and the method is suitable for long-distance and high-safety quantum communication and quantum network deployment.

Description

Technical Field

[0001] This invention relates to the field of quantum key distribution technology, and more specifically to a method, apparatus, and system for source-device-independent quantum key distribution and its network. Background Technology

[0002] Quantum key distribution (QKD) is a long-distance key-sharing technology based on quantum physics principles to achieve information-theoretically secure key sharing. It is the closest technology in the field of quantum information to practical application. However, significant differences exist between actual devices and ideal models, potentially leading to security vulnerabilities and exposing the system to eavesdropping risks. To bridge this gap, researchers proposed device-independent quantum key distribution protocols, but these place extremely high demands on device performance, making them difficult to implement over long distances. Subsequently, measurement-device-independent quantum key distribution protocols and their variants were proposed. These protocols can defend against various attacks on the detector side, and experiments have shown efficient long-distance key distribution. In this context, source-end security becomes the main weakness of quantum key distribution systems.

[0003] To address source-side security issues, existing technologies have proposed various improvement schemes, including loss-tolerant protocols, side-channel security schemes, and fully passive protocols. These methods can mitigate the risks posed by source-side defects to some extent, but they still cannot cover all potential attacks. For example, the recently discovered hidden multidimensional modulation side-channel can introduce security vulnerabilities and significantly limit transmission distance. Some unknown side-channel attacks may lead to serious security risks.

[0004] In recent years, non-classical quantum light sources have attracted widespread attention as an important resource for quantum networks. These non-classical light sources refer to quantum light sources capable of emitting high-purity single-photon states, such as single-photon sources and Schrödinger's cat states. The introduction of non-classical light sources into fabrication-measurement quantum key distribution protocols has achieved phased experimental progress, such as long-distance quantum key distribution and metropolitan high-speed quantum communication experiments based on single-photon sources, and in some scenarios, it has even surpassed the performance of decoy state protocols based on weakly coherent light sources. However, existing schemes still suffer from source-side channel risks, making it difficult to fully realize the potential of non-classical light sources compared to traditional laser sources in terms of security and performance.

[0005] Therefore, researching quantum key distribution protocols that do not rely on source-end security assumptions has become an urgent problem to be solved in this field. Summary of the Invention

[0006] Objective of this invention: To provide a source-device-independent quantum key distribution method, apparatus, and system, which solves the problem that existing quantum key distribution protocols rely on source-side security assumptions, effectively resisting potential attacks against the source device, while improving key generation rate and transmission distance. Furthermore, this invention extends to multi-user source-device-independent quantum key distribution networks, addressing the complexity of existing entangled source-based quantum network structures and achieving a more secure and scalable quantum key distribution network through a more easily deployable experimental system.

[0007] Technical solution: To achieve the above objectives, the present invention includes the following four aspects:

[0008] Firstly, the source device-independent quantum key distribution method of the present invention includes five steps: photon emission, signal measurement, basis selection, parameter estimation, and post-selection, the specific process of which is as follows:

[0009] (1) Photon emission: The untrusted first transmitter uses a non-classical quantum light source, in time sequence. A quantum signal light pulse with high single-photon purity is emitted and sent to two trusted measurement terminals through a state distribution process;

[0010] (2) Signal measurement: Under a unified measurement scheme, the first and second measurement ends randomly select the measurement basis vector of each optical pulse and record the corresponding detection response events and measurement information;

[0011] (3) Basis vector screening: The first and second measurement ends disclose the measurement basis vector information, screen and retain valid response events that meet the predefined conditions, generate the original bit value string according to the bit mapping rules, and then select the measurement method to form an entangled association between the measurement ends;

[0012] (4) Parameter estimation: The measurement end uses an auxiliary basis to estimate parameters according to the pre-selected measurement scheme and uses a signal basis to extract the original key;

[0013] (5) Post-processing: The measurement end performs classical error correction, error verification and privacy amplification on the original key string to obtain the final security key.

[0014] Preferably, the non-classical light source in step (1) is a quantum light source capable of generating a state with high single-photon purity, such as a single-photon source or a Schrödinger cat state.

[0015] Preferably, the measurement scheme can be based on time, phase, or polarization degrees of freedom; the measurement basis vector can be a time-domain basis vector, an interferometric basis vector, or a polarization basis vector, wherein the time-domain basis vector is used to perform photon detection for each time window; the interferometric basis vector is used to perform interferometric measurement on light pulses in adjacent time windows; and the polarization basis vector is used to measure the polarization state of each light pulse.

[0016] Preferably, steps (4) and (5) can be implemented using standard security analysis methods in existing quantum key distribution systems, including but not limited to error estimation methods based on random sampling and statistical fluctuations.

[0017] Secondly, the present invention includes a source-device-independent quantum key distribution system, comprising a first transmitting end, a first measuring end, and a second measuring end. The first transmitting end includes a photon preparation module and a state distribution module. The photon preparation module is used to transmit states with high-purity single-photon components, whose second-order correlation function... The value is much smaller than 1, which approximates the degree of suppression of multiphoton components; the state distribution module is used to randomly distribute the optical pulse sequence to the first and second measurement ends by means of optical path switching or probability beam splitting:

[0018] The measurement end includes a measurement module, which is used to realize the selection of measurement basis vectors, the measurement of single-photon-level light pulses, and data recording.

[0019] The first transmitting end, the first measuring end, and the second measuring end each include a post-processing module. The post-processing module is used to control each module of the local end, and to perform subsequent filtering of the original key, classical error correction, error verification, and privacy amplification to obtain the final key.

[0020] Preferably, the photon preparation module includes a non-classical quantum light source, which may be a single-photon source or a Schrödinger cat state, etc., for transmitting states with high-purity single-photon components; the state distribution module may include a 1×2 balanced beam splitter for randomly distributing the optical pulse sequence to the first measurement end and the second measurement end; the state distribution module may also adopt an equivalent distribution structure based on polarization state, which can realize the distribution of polarization state through a structure including an optical switch, a polarization controller and a polarization beam splitter.

[0021] Preferably, the measurement module is used to randomly select measurement basis vectors and detect received single-photon-level light pulses, including an optical path beam splitting structure and measurement units corresponding to different measurement basis vectors; the optical path beam splitting structure is used to randomly select measurement basis vectors; the measurement unit may be: a time-domain measurement module, used to perform photon detection on light pulses in each time window, preferably using a single-photon detector; an interferometric measurement module, used to realize interferometric measurement of light pulses in adjacent time windows, preferably using an asymmetric Mach-Zehnder interferometer structure; and a polarization measurement module, used to realize polarization state measurement of each light pulse, preferably using a polarization controller, a polarization beam splitter, and a single-photon detector.

[0022] Thirdly, the present invention also includes a source-device-independent quantum key distribution network method, comprising the following steps:

[0023] (1) Photon emission: The untrusted first transmitter uses a non-classical quantum light source, in time sequence. A quantum signal light pulse with high single-photon purity is emitted and sent to n measurement terminals through a state distribution process;

[0024] (2) Signal measurement: Under the same measurement scheme, from the first measurement end to the nth measurement end, the measurement basis vector of the received optical pulse signal is randomly selected for measurement, and the corresponding detection response event and measurement information are recorded;

[0025] (3) Basis vector screening: All measurement ends publish measurement basis vector information, screen and retain valid response events that meet the predefined conditions, generate original bit value strings according to bit mapping rules; when more than two measurement ends obtain valid response events at the same time, randomly select two of them and retain the corresponding detection events, and form an entangled association between any two measurement ends by the method of subsequent selection measurement.

[0026] (4) Parameter estimation: The measurement end uses an auxiliary basis to estimate parameters according to the pre-selected measurement scheme and uses a signal basis to extract the original key;

[0027] (5) Post-processing: The original key string is subjected to classical error correction, error verification and privacy amplification from the first measurement end to the nth measurement end to obtain the final security key.

[0028] Preferably, the non-classical light source in step (1) is a quantum light source capable of generating a state with high single-photon purity, such as a single-photon source or a Schrödinger cat state.

[0029] Preferably, the measurement scheme can be based on time, phase, or polarization degrees of freedom; the measurement basis vector can be a time-domain basis vector, an interferometric basis vector, or a polarization basis vector, wherein the time-domain basis vector is used to perform photon detection for each time window; the interferometric basis vector is used to perform interferometric measurement on light pulses in adjacent time windows; and the polarization basis vector is used to measure the polarization state of each light pulse.

[0030] Preferably, steps (4) and (5) can be implemented using standard security analysis methods in existing quantum key distribution systems, including but not limited to error estimation methods based on random sampling and statistical fluctuations.

[0031] Fourthly, the present invention also includes a source-device-independent quantum key distribution network system, comprising a first transmitting end, a first measurement end to an nth measurement end, wherein the first transmitting end includes a photon preparation module and a state distribution module; wherein the photon preparation module is used to transmit a state with a high-purity single-photon component, the second-order correlation function of which is... The value is much smaller than 1, which approximates the degree of suppression of multiphoton components; the state distribution module is used to randomly distribute the optical pulse sequence to n measurement ends by means of optical path switching or probability beam splitting:

[0032] The measurement end includes a measurement module, which is used to realize the selection of measurement basis vectors, the measurement of single-photon-level light pulses, and data recording.

[0033] The first transmitting end and the first to nth measuring ends each include a post-processing module. The post-processing module is used to control each module of the local end, and to perform subsequent screening of the original key, classical error correction, error verification and privacy amplification to obtain the final key.

[0034] Preferably, the photon preparation module includes a non-classical quantum light source, which can be a single-photon source or a Schrödinger's cat state, etc., for transmitting states with high-purity single-photon components; the state distribution module can include a 1×n balanced beam splitter for randomly distributing the optical pulse sequence to the first to the nth measurement ends; the state distribution module can also adopt an equivalent distribution structure based on polarization states, including an optical switch matrix and a polarization beam splitter network. A polarization controller and a polarization beam splitter are used to realize the distribution of polarization states.

[0035] Preferably, the measurement module is used to randomly select measurement basis vectors in a preset measurement scheme and detect received single-photon-level light pulses, including an optical path beam splitting structure and measurement units corresponding to different measurement basis vectors; the optical path beam splitting structure is used to randomly select measurement basis vectors; the measurement unit may be: a time-domain measurement module, used to perform photon detection on light pulses in each time window, preferably using a single-photon detector; an interferometric measurement module, used to realize interferometric measurement of light pulses in adjacent time windows, preferably using an asymmetric Mach-Zehnder interferometer structure; and a polarization measurement module, used to realize polarization state measurement of each light pulse, preferably using a polarization controller, a polarization beam splitter, and a single-photon detector.

[0036] Beneficial effects: The advantages of this invention compared to the prior art are as follows:

[0037] (1) The source-device-independent quantum key distribution protocol and system proposed in this invention solves the security vulnerabilities at the source end and can effectively resist all known and potential attacks against the source end. Current quantum key distribution protocols all require theoretical security assumptions about the source end device. Although some technologies can cope with specific types of attacks, there are still many potential and unknown attacks that threaten the security of the source end. This invention utilizes the physical characteristics of non-classical light sources (capable of emitting high-purity single-photon states) to achieve source-device-independent security that is difficult to achieve with traditional laser sources, and has significant quantum advantages in terms of security and performance.

[0038] (2) The source-device-independent quantum key distribution network and system proposed in this invention achieve source-end security while reducing the deployment difficulty of practical quantum key distribution networks. At present, multi-user network protocols based on entangled photon sources can achieve source-independent security, but they rely on complex technologies such as preparing entangled photon pairs and wavelength division multiplexing. Their system complexity increases significantly with the number of users. This invention effectively reduces the implementation complexity by directly extending the point-to-point protocol to the multi-user network protocol. It has advantages in implementation efficiency and scalability, and has high practical value in the construction of long-distance, high-security quantum networks in the future. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 This is a schematic diagram of the source device-independent quantum key distribution system of the present invention;

[0041] Figure 2 This is a simulation result diagram of the code generation rate in Embodiment 1 of the present invention;

[0042] Figure 3 This is a schematic diagram of the system in Embodiment 2 of the present invention;

[0043] Figure 4 This is a schematic diagram of the system in Embodiment 3 of the present invention;

[0044] Figure 5 This is a schematic diagram of the source device-independent quantum key distribution network system of the present invention;

[0045] Figure 6 This is a schematic diagram of the basis vector screening process in Embodiment 4 of the present invention;

[0046] Figure 7 This is a diagram showing the simulation results of the code generation rate in Embodiment 4 of the present invention. Detailed Implementation

[0047] The technical solutions in the embodiments described herein will be clearly and completely described below with reference to the accompanying drawings. These descriptions are exemplary only and are not intended to limit the scope of the invention. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments described herein, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0048] Example 1

[0049] This embodiment exemplifies an implementation of the source-device-independent quantum key distribution method and system described in this invention, based on a time-degree-of-freedom measurement scheme. For example... Figure 1 As shown, the system for executing this method includes a first transmitting end, a first measuring end, and a second measuring end.

[0050] The first transmitting end includes a photon preparation module and a state distribution module. The photon preparation module utilizes a non-classical light source, such as a single-photon source or a Schrödinger's cat state, to transmit states with high-purity single-photon components, whose second-order correlation function... The value is much smaller than 1 to approximate the degree of suppression of multiphoton components; the state distribution module consists of a 1×2 balanced beam splitter for randomly distributing the optical pulse sequence to the first and second measurement ends. The transmitting and measuring ends are connected by a quantum channel made of extremely low-loss optical fiber.

[0051] Both the first and second measurement ends include measurement modules. These modules are used to perform interferometric basis vector measurements or time-domain basis vector measurements of single-photon-level optical pulses, as well as data recording. Specifically, each measurement module includes a 1×2 beam splitter, an interferometric measurement module, and a time-domain measurement module. The output of the 1×2 beam splitter is connected to both the interferometric and time-domain measurement modules, passively and randomly selecting the measurement mode for each optical pulse. The interferometric measurement module includes an asymmetric Mach-Zehnder interferometer for interferometric measurements of optical pulses in adjacent time windows. This module includes a 1×2 beam splitter, a 2×2 beam splitter, and two detectors. The input optical pulse signal is split by the 1×2 beam splitter and then interfered by the 2×2 beam splitter. The two outputs of each 2×2 beam splitter are connected to the left and right detectors, respectively. The detectors perform interferometric measurements on adjacent optical pulses. The time-domain measurement module includes a single-photon detector for photon measurements of optical pulses in each time window.

[0052] The first transmitting end and all measuring ends also include a post-processing module. This post-processing module controls the modules on its own end and performs subsequent measurement pairing, basis vector selection, classical error correction, error verification, and privacy amplification processes to obtain the final key. For simplicity, the post-processing module is not shown in the illustration.

[0053] The source-device-independent quantum key distribution method of Embodiment 1 of the present invention includes five steps: photon emission, signal measurement, basis selection, parameter estimation, and post-selection. The specific process is as follows:

[0054] (1) Photon emission: The untrusted first transmitter uses a non-classical quantum light source, in time sequence. A quantum signal light pulse with high single-photon purity is emitted and sent to the measurement end through a state distribution process;

[0055] (2) Signal Measurement: The first and second measurement ends each use a beam splitter to randomly select the measurement basis vector for each optical pulse: either the interference basis vector or the time-domain basis vector, and record the corresponding response events: under the interference basis vector, for adjacent time windows Interferometric measurements are performed using light pulses, and the detection response events and corresponding detectors are recorded. If both detectors at the same measurement end respond, one detector is randomly recorded. Each measurement end includes two detectors, left and right, denoted as... Under the time-domain basis vectors, photon detection is performed on the light pulses in each time window, and the events of the detector response and the corresponding time window are recorded. Front and back windows and The response status;

[0056] (3) Basis selection: For response events measured under interferometric basis, the first and second measurement ends obtain the bit values ​​of the X basis according to their respective measured time windows and detector information; for response events obtained under time-domain basis, the first and second measurement ends perform a pairing process respectively, retain valid response events, and then obtain the bit values ​​of the Z basis according to the bit mapping rule. The specific process is as follows:

[0057] For response events measured under the interferometric basis, the response events obtained by the first and second measurement ends within the same time window are retained and denoted as valid detection events of the X basis. When the detector recording the response is on the left, i.e. or The corresponding measurement end records the bit value of the X basis vector as 0; when the detector recording the response is on the right, i.e. or The corresponding measurement end records the bit value of the X basis vector as 1;

[0058] For response events measured under the time-domain basis vectors, firstly, the first measurement end generates a string of events of the same length based on the number of response events in the time-domain basis vectors. random numbers Pair each response event individually: when When the time window is reached, discard the response of the next time window and pair it with the response of the previous time window. ;when When the time window is reached, discard the response from the previous time window and pair it with the response from the next time window. When a pairing reuses a time window that has already been paired, the pairing is discarded; the first measuring end transmits the retained pairing information to the second measuring end through the classic channel;

[0059] Next, the second measurement end, based on the response events it measures under the time-domain basis, retains the pairings containing the time windows corresponding to the response events, denoted as valid detection events of the Z basis, and transmits the retained valid event information to the first measurement end;

[0060] Finally, the first and second measuring ends obtain the bit values ​​of the Z basis vectors according to the bit mapping rules, which are as follows: for each retained valid pair, if the previous time window responds but the next does not, the first measuring end records the bit value of the Z basis vector as 0, and the second measuring end records the bit value of the Z basis vector as 1; if the next time window responds but the previous one does not, the first measuring end records the bit value of the Z basis vector as 1, and the second measuring end records the bit value of the Z basis vector as 0; if both the previous and next time windows respond, the measuring end randomly discards one of the responses and records the bit value of the corresponding case.

[0061] (4) Parameter estimation: Both the first and second measurement terminals publish the bit values ​​of all X basis vectors, and calculate the bit error rate under the X basis vectors. Phase error rate under Z basis vectors The parameter estimation results are obtained, and the specific implementation steps are as follows:

[0062] S1: Total gain through the X basis vectors and error gain The number of response events and the number of error events for the X basis vector are calculated: , ,in, The probability of choosing the interference basis vectors;

[0063] S2: Calculate the bit error rate of the X basis vector. ;

[0064] S3: Total gain through the Z basis vectors The number of response events for the Z basis vectors is calculated. ,in, The probability of choosing time-domain basis vectors;

[0065] S4: Using the random sampling without replacement formula, obtain the upper limit of the phase error rate of the Z basis vectors: ,in, This refers to the statistical fluctuations resulting from random sampling without replacement. This is the failure probability coefficient;

[0066] (5) Post-processing: The parameter estimation results are used to perform classical error correction, error verification, and privacy amplification on the bit value string of the Z basis vectors to obtain the final key:

[0067]

[0068] The maximum amount of information leaked during the classic error correction process is [missing information]. ,in To improve error correction efficiency, For binary Shannon entropy, Let Z be the bit error rate of the basis vector. , This represents the failure probability coefficient during post-processing.

[0069] like Figure 2As shown, the source-device-independent quantum key distribution method of the present invention can be used to achieve secure and efficient quantum key distribution under conditions where the source device is untrusted. It removes the theoretical requirement of source-end security assumptions and can achieve secure transmission distances exceeding 400 kilometers. The secure code rate of the present invention surpasses existing single-photon source BB84 protocols and laser-based decoy state BB84 protocols over long distances, exhibiting significant advantages in both security and transmission distance.

[0070] Example 2

[0071] This embodiment exemplifies an implementation of the source-device-independent quantum key distribution method and system described in this invention, based on a phase degree of freedom measurement scheme. For example... Figure 3 As shown, the system for executing this method includes a first transmitting end, a first measuring end, and a second measuring end.

[0072] The first transmitting end includes a photon preparation module and a state distribution module. The photon preparation module utilizes a non-classical light source, such as a single-photon source or a Schrödinger's cat state, to transmit single-photon components with high purity. The state distribution module consists of a 1×2 balanced beam splitter used to randomly distribute the optical pulse sequence to the first and second measurement ends. The transmitting and measuring ends are connected by a quantum channel made of extremely low-loss optical fiber.

[0073] Both the first and second measurement ends include measurement modules, which are used to perform interferometric measurements and data recording of single-photon-level optical pulses. Specifically, the measurement module includes a phase modulator and an interferometric measurement module, wherein the phase modulator is used to randomly modulate the phase of each optical pulse (…). or The phase difference between adjacent pulses is changed to select the measurement basis (X or Y basis). The interferometric measurement module includes an asymmetric Mach-Zehnder interferometer for interferometric measurement of light pulses in adjacent time windows. It includes a 1×2 beam splitter, a 2×2 beam splitter, and two single-photon detectors. The two outputs of the 1×2 beam splitter are connected to the input of the 2×2 beam splitter, and the outputs of the 2×2 beam splitter are connected to the left and right detectors, respectively.

[0074] The first transmitting end and all measuring ends also include a post-processing module. This post-processing module controls the modules on its own end and performs subsequent measurement pairing, basis vector selection, classical error correction, error verification, and privacy amplification processes to obtain the final key. For simplicity, the post-processing module is not shown in the illustration.

[0075] The source device-independent quantum key distribution method of Embodiment 2 of the present invention includes the following steps:

[0076] (1) Photon emission: The untrusted first transmitter uses a non-classical quantum light source, in time sequence. A quantum signal light pulse with high single-photon purity is emitted and sent to the measurement end through a state distribution process;

[0077] (2) Signal Measurement: The first and second measurement ends each use a phase modulator to randomly select the measurement basis vector for each optical pulse: the X basis vector or the Y basis vector, by adjusting the phase difference between adjacent pulses to... Under the X(Y) basis, for adjacent time windows Interferometric measurements are performed using light pulses, and the detection response events and corresponding detectors are recorded. If both detectors at the same measurement end respond, one detector is randomly recorded. Each measurement end includes two detectors, left and right, denoted as […]. ;

[0078] (3) Basis vector selection: The first and second measurement ends publish the measurement basis vectors, retain the response events measured under the same basis vectors, and then obtain the bit values ​​of the X basis vector and the Y basis vector according to the bit mapping rule. The bit mapping rule is as follows:

[0079] When the detector recording the response is on the left, i.e. or The corresponding measurement end records the bit value of the X(Y) basis vector as 0; when the detector recording the response is on the right, i.e. or The corresponding measurement end records the bit value of the X (Y) basis vector as 1;

[0080] (4) Parameter estimation: Both the first and second measurement terminals publish the bit values ​​of all Y basis vectors, and calculate the bit error rate under the Y basis vectors. Phase error rate under X basis The parameter estimation results are obtained, and the specific implementation steps are as follows:

[0081] S1: Total gain through the Y basis vectors and error gain The number of response events and the number of error events for the Y basis vectors are calculated: , ,in, The probability of selecting the Y measurement basis vector;

[0082] S2: Calculate the bit error rate of the Y basis vector. ;

[0083] S3: Total gain through the X basis vector The number of response events for the X basis vector is calculated. ,in, The probability of selecting the basis vectors for X;

[0084] S4: Using the random sampling without replacement formula, obtain the upper limit of the phase error rate of the X basis vector: ,in, This refers to the statistical fluctuations resulting from random sampling without replacement. This is the failure probability coefficient;

[0085] (5) Post-processing: The results of parameter estimation are used to perform classical error correction, error verification, and privacy amplification on the bit value string of the X basis vector to obtain the final key:

[0086]

[0087] The maximum amount of information leaked during the classic error correction process is [missing information]. ,in To improve error correction efficiency, For binary Shannon entropy, Let X be the bit error rate of the basis vector. , This represents the failure probability coefficient during post-processing.

[0088] Example 3

[0089] This embodiment exemplifies an implementation of the source-device-independent quantum key distribution method and system described in this invention, based on a polarization degree-of-freedom measurement scheme. For example... Figure 4 As shown, the system for executing this method includes a first transmitting end, a first measuring end, and a second measuring end.

[0090] The first transmitting end includes a photon preparation module and a state distribution module. The photon preparation module utilizes a non-classical light source, such as a single-photon source or a Schrödinger's cat state, to transmit single-photon components with high purity. The state distribution module includes a polarization control module, a time-division optical path switching module, and a 2×2 polarization beam splitter. The polarization control module includes a linear polarizer and a half-wave plate. The linear polarizer is used to control the single-photon number state. Adding polarization degrees of freedom yields the initial polarization state. The half-wave plate is used to... The state linear transformation is The time-division optical path switching module is used to switch between odd and even time windows, and can transmit optical pulses at odd times to the upper optical fiber and optical pulses at even times to the lower optical fiber through an optical switch; the 2×2 polarization beam splitter is used to randomly distribute the optical pulse sequence to the first measurement end and the second measurement end. The transmitting end and the measuring end are connected by a quantum channel made of extremely low-loss optical fiber.

[0091] Both the first and second measurement ends include measurement modules, which are used to measure the polarization state of single-photon-level optical pulses and record data. Specifically, the measurement module includes a 1×2 beam splitter, a Z-basis measurement module, and an X-basis measurement module. The output of the 1×2 beam splitter is connected to the Z-basis measurement module and the X-basis measurement module, respectively, for passively and randomly selecting the measurement mode used for each optical pulse. The Z-basis measurement module includes a polarization beam splitter and two single-photon detectors. The output of the polarization beam splitter is connected to the detectors... and detector Connection, the detector and detector Used to measure the eigenstates of linearly polarized basis vectors (Z basis vectors) The X-radix measurement module includes a half-wave plate, a polarization beam splitter, and two single-photon detectors. The half-wave plate is used to... linear transformation of state to The output terminals of the polarization beam splitter are respectively connected to the detector. and detector Connection, the detector and detector Used to measure the eigenstates of diagonal basis vectors respectively .

[0092] The first transmitting end and all measuring ends also include a post-processing module. This post-processing module controls the modules on its own end and performs subsequent measurement pairing, basis vector selection, classical error correction, error verification, and privacy amplification processes to obtain the final key. For simplicity, the post-processing module is not shown in the illustration.

[0093] The source device-independent quantum key distribution method of Embodiment 3 of the present invention includes the following steps:

[0094] (1) Photon emission: The untrusted first transmitter uses a non-classical quantum light source, in time sequence. A quantum signal light pulse with high single-photon purity is emitted and sent to the measurement end through a state distribution process;

[0095] (2) Signal measurement: The first and second measurement ends each use a beam splitter to randomly select the measurement basis vector of each optical pulse: linear polarization basis vector (Z basis vector) or diagonal polarization basis vector (X basis vector), record the detection response event and the corresponding detector, and each measurement end includes four detection ports, corresponding to the four polarization states of the BB84 protocol;

[0096] (3) Basis vector selection: The first and second measurement terminals publish the measurement basis vectors, retain the response events measured under the same basis vectors, and then obtain the bit values ​​of the Z basis vector and the X basis vector according to the bit mapping rules. The specific process is as follows:

[0097] The four measurement ports of each measurement end correspond to the four polarization states of the BB84 protocol: eigenstates of linear basis vectors. and the eigenstates of the diagonal basis vectors. These four polarization states are mapped to bit values ​​0 and 1 of the Z basis vector and bit values ​​0 and 1 of the X basis vector, respectively.

[0098] (4) Parameter estimation: Both the first and second measurement terminals publish the bit values ​​of all X basis vectors, and calculate the bit error rate under the X basis vectors. Phase error rate under Z basis vectors The parameter estimation results are obtained, and the specific implementation steps are as follows:

[0099] S1: Total gain through the X basis vectors and error gain The number of response events and the number of error events for the X basis vector are calculated: , ,in, Let X be the probability of choosing the basis vector X;

[0100] S2: Calculate the bit error rate of the X basis vector. ;

[0101] S3: Total gain through the Z basis vectors The number of response events for the Z basis vectors is calculated. ,in, The probability of choosing the Z basis vector;

[0102] S4: Using the random sampling without replacement formula, obtain the upper limit of the phase error rate of the Z basis vectors: ,in, This refers to the statistical fluctuations resulting from random sampling without replacement. This is the failure probability coefficient;

[0103] (5) Post-processing: The parameter estimation results are used to perform classical error correction, error verification, and privacy amplification on the bit value string of the Z basis vectors to obtain the final key:

[0104]

[0105] The maximum amount of information leaked during the classic error correction process is [missing information]. ,in To improve error correction efficiency, For binary Shannon entropy, Let Z be the bit error rate of the basis vector. , This represents the failure probability coefficient during post-processing.

[0106] Example 4

[0107] This embodiment utilizes the source-device-independent quantum key distribution network method provided by the present invention to implement a quantum key distribution network with source-independent security, specifically employing a measurement scheme based on time degrees of freedom. For example... Figure 5 As shown, the system that executes this method includes a first transmitting end and a first measuring end, a second measuring end, ... up to the nth measuring end. Each end works together to complete the quantum key distribution process.

[0108] The first transmitting end includes a photon preparation module and a state distribution module. The photon preparation module utilizes a non-classical light source, such as a single-photon source or a Schrödinger's cat state, to transmit single-photon components with high purity. The state distribution module consists of a 1×n beam splitter, used to randomly distribute the optical pulse sequence to the first to the nth measurement ends. The transmitting and measuring ends are connected by a quantum channel made of extremely low-loss optical fiber.

[0109] Each measurement end includes a measurement module, which is used to perform interferometric or time-domain measurements of single-photon-level optical pulses, as well as data recording. Specifically, the measurement module includes a 1×2 beam splitter, an interferometric measurement module, and a time-domain measurement module. The output of the 1×2 beam splitter is connected to both the interferometric measurement module and the time-domain measurement module, and is used to passively and randomly select the measurement mode for each optical pulse. The interferometric measurement module includes an asymmetric Mach-Zehnder interferometer, used to perform interferometric measurements of optical pulses in adjacent time windows. It includes a 1×2 beam splitter, a 2×2 beam splitter, and two detectors. The input optical pulse signal is split by the 1×2 beam splitter and then interfered by the 2×2 beam splitter. The two outputs of each 2×2 beam splitter are connected to the left and right detectors, respectively. The detectors perform interferometric measurements on adjacent optical pulses. The time-domain measurement module includes a single-photon detector, used to perform photon measurements for each optical pulse.

[0110] The first transmitting end and all measuring ends also include a post-processing module. This post-processing module controls the modules on its own end and performs subsequent measurement pairing, basis vector selection, classical error correction, error verification, and privacy amplification processes to obtain the final key. For simplicity, the post-processing module is not shown in the illustration.

[0111] The source device-independent quantum key distribution network method of this embodiment includes the following steps:

[0112] (1) Photon emission: The untrusted first transmitter uses a non-classical quantum light source, in time sequence. A quantum signal light pulse with high single-photon purity is emitted and sent to n measurement terminals through a state distribution process;

[0113] (2) Signal Measurement: From the first measurement end to the nth measurement end, a beam splitter is used to randomly select the measurement basis vector for each optical pulse: either the interference basis vector or the time-domain basis vector, and the corresponding response events are recorded. Under the interference basis vector, the measurement of adjacent time windows is recorded. Interferometric measurements are performed using light pulses, and the detection response events and corresponding detectors are recorded. If both detectors at the same measurement end respond, one detector is randomly recorded. Each measurement end includes two detectors, left and right, denoted as... Under the time-domain basis vectors, photon detection is performed on the light pulses in each time window, and the events of the detector response and the corresponding time window are recorded. Front and back windows and The response status;

[0114] (3) Basis selection: For response events obtained under the interferometric basis, all measurement ends publish their respective time windows and detector response information to obtain the bit value of the X basis; for response events obtained under the time-domain basis, a pairing process is performed sequentially from the first measurement end to the nth measurement end, retaining valid response events, and then obtaining the bit value of the Z basis according to the bit mapping rule; such as Figure 6 As shown, the specific process is as follows:

[0115] For response events measured under the interferometric basis vectors, a time window is reserved where at least two measurement ends produce responses simultaneously. If more than two measurement ends produce responses, two measurement ends are randomly selected. , A valid response is denoted as a valid detection event of the X basis vector; when the detector recording the response is on the left, i.e. The corresponding measurement end records the bit value of the X basis vector as 0; when the detector recording the response is on the right, i.e. The corresponding measurement end records the bit value of the X basis vector as 1;

[0116] For the response events measured under the time-domain basis vectors, a pairing process is performed sequentially from the first measurement end to the nth measurement end, valid response events are retained, and then the bit values ​​of the Z basis vectors are obtained according to the bit mapping relationship. The specific steps are as follows:

[0117] S1: The first measurement end generates a string of events of the same length based on the number of response events measured under the time-domain basis vectors. random numbers Pair the response events of each of its temporal basis vectors: when When the time window is reached, discard the response of the next time window and pair it with the response of the previous time window. ;when When the time window is reached, discard the response from the previous time window and pair it with the response from the next time window. When a pairing reuses a time window that has already been paired, the pairing is discarded; the first measuring end transmits the retained pairing information to the second measuring end through the classic channel up to the nth measuring end;

[0118] S2: From the second to the nth measurement end, based on the response events measured under the time-domain basis vectors, retain the pairings containing the time windows corresponding to the response events. If more than two measurement ends retain the same pairing, then two measurement ends are randomly selected from them. , As a valid response, it is denoted as a valid detection event of the Z basis vector;

[0119] S3: All measurement terminals obtain the bit values ​​of the Z basis vector according to the bit mapping rule, which is: for each retained valid pair, when the previous time window responds but the next does not, the measurement terminal with the smaller ordinal number... Record the bit value of the Z basis vector as 0, and measure the end with the larger ordinal number. Record the bit value of the Z basis vector as 1; when the latter time window responds while the former does not, the measurement end with the smaller ordinal number... Record the bit value of the Z basis vector as 1, and measure the end with the larger ordinal number. Record the bit value of the Z basis vector as 0; when there is a response in both the preceding and following time windows, the measuring end randomly discards one of the responses and records the corresponding bit value.

[0120] S4: Discard the time windows corresponding to the effective detection events of the Z basis vectors that are ultimately retained above, and do not reuse them in subsequent steps;

[0121] S5: Execute S1-S4 sequentially from the second measuring end to the nth measuring end;

[0122] (4) Parameter estimation: The bit values ​​of all X basis vectors are published from the first measurement end to the nth measurement end, and the bit error rate under the X basis vectors is calculated. Phase error rate under Z basis vectors The parameter estimation results are obtained, and the specific implementation steps are as follows:

[0123] S1: Total gain through the X basis vectors and error gain The number of response events and the number of error events for the X basis vector are calculated: , ,in, The probability of choosing the interference basis vectors;

[0124] S2: Calculate the bit error rate of the X basis vector. ;

[0125] S3: Total gain through the Z basis vectors The number of response events for the Z basis vectors is calculated. ,in, The probability of choosing time-domain basis vectors;

[0126] S4: Using the random sampling without replacement formula, obtain the upper limit of the phase error rate of the Z basis vectors: ,in, This refers to the statistical fluctuations resulting from random sampling without replacement. This is the failure probability coefficient;

[0127] (6) Post-processing: The parameter estimation results are used to perform classical error correction, error verification, and privacy amplification on the bit value string of the Z basis vectors to obtain the final key:

[0128]

[0129] The maximum amount of information leaked during the classic error correction process is [missing information]. ,in To improve error correction efficiency, For binary Shannon entropy, Let Z be the bit error rate of the basis vector. , This represents the failure probability coefficient during post-processing.

[0130] like Figure 7 As shown, this invention directly extends the point-to-point source-device-independent quantum key distribution method to multi-user application scenarios, constructing a secure and efficient quantum network. Compared to existing quantum networks based on entangled photon sources, this invention reduces the system complexity of network deployment, enhances the scalability of the protocol by utilizing the physical characteristics of non-classical quantum light sources, and achieves an increase in the security code rate as the number of users increases, demonstrating its potential for widespread application in long-distance, high-security quantum communication networks.

Claims

1. A source-device-independent quantum key distribution method, characterized in that, Includes the following steps: (1) Photon emission: The untrusted first transmitter uses a non-classical quantum light source, in time sequence. A quantum signal light pulse with high single-photon purity is emitted and sent to two trusted measurement terminals through a state distribution process; (2) Signal measurement: Under a unified measurement scheme, the first and second measurement ends randomly select the measurement basis vector of each optical pulse and record the corresponding detection response events and measurement information; (3) Basis vector screening: The first and second measurement ends disclose the measurement basis vector information, screen and retain valid response events that meet the predefined conditions, generate the original bit value string according to the bit mapping rules, and then select the measurement method to form an entangled association between the measurement ends; (4) Parameter estimation: The measurement end uses an auxiliary basis to estimate parameters according to the pre-selected measurement scheme and uses a signal basis to extract the original key; (5) Post-processing: The first and second measurement ends perform classical error correction, error verification and privacy amplification on the original key string to obtain the final security key.

2. The source-device-independent quantum key distribution method according to claim 1, characterized in that, The non-classical light source in step (1) is a quantum light source capable of generating a state with high single-photon purity, such as a single-photon source or a Schrödinger cat state.

3. The source-device-independent quantum key distribution method according to claim 1, characterized in that, The measurement scheme can be based on time, phase, or polarization degrees of freedom; the measurement basis vector can be a time-domain basis vector, an interferometric basis vector, or a polarization basis vector, wherein the time-domain basis vector is used to perform photon detection for each time window; the interferometric basis vector is used to perform interferometric measurement on light pulses in adjacent time windows; and the polarization basis vector is used to measure the polarization state of each light pulse.

4. A system based on the source device-independent quantum key distribution method of claim 1, characterized in that, The system includes a first transmitting end, a first measuring end, and a second measuring end. The first transmitting end includes a photon preparation module and a state distribution module. The photon preparation module is used to transmit states with high-purity single-photon components, whose second-order correlation function... The value is much smaller than 1 to approximate the degree of suppression of multiphoton components; the state distribution module is used to randomly distribute the optical pulse sequence to the first measurement end and the second measurement end by means of optical path switching or probability beam splitting. The measurement end includes a measurement module, which is used to realize the selection of measurement basis vectors, the measurement of single-photon-level light pulses, and data recording. The first transmitting end, the first measuring end, and the second measuring end each include a post-processing module. The post-processing module is used to control each module of the local end, and to perform subsequent filtering of the original key, classical error correction, error verification, and privacy amplification to obtain the final key.

5. The system of the source device-independent quantum key distribution method according to claim 4, characterized in that: The photon preparation module includes a non-classical quantum light source, which can be a single-photon source or a Schrödinger cat state, etc., to transmit states with high-purity single-photon components; the state distribution module can include a 1×2 balanced beam splitter to randomly distribute the optical pulse sequence to the first and second measurement ends; the state distribution module can also adopt an equivalent distribution structure based on polarization state, which can realize the distribution of polarization state through a structure including an optical switch, a polarization controller and a polarization beam splitter.

6. The system of the source device-independent quantum key distribution method according to claim 3, characterized in that: The measurement module is used to randomly select measurement basis vectors and detect received single-photon-level light pulses. It includes an optical path beam splitting structure and measurement units corresponding to different measurement basis vectors. The optical path beam splitting structure is used to randomly select measurement basis vectors. The measurement unit may be: a time-domain measurement module for photon detection of light pulses in each time window, preferably using a single-photon detector; an interferometric measurement module for interferometric measurement of light pulses in adjacent time windows, preferably using an asymmetric Mach-Zehnder interferometer structure; and a polarization measurement module for measuring the polarization state of each light pulse, preferably using a polarization controller, a polarization beam splitter, and a single-photon detector.

7. A source-device-independent quantum key distribution network method, characterized in that, Includes the following steps: (1) Photon emission: The untrusted first transmitter uses a non-classical quantum light source, in time sequence. A quantum signal light pulse with high single-photon purity is emitted and sent to n measurement terminals through a state distribution process; (2) Signal measurement: Under the same measurement scheme, from the first measurement end to the nth measurement end, the measurement basis vector of the received optical pulse signal is randomly selected for measurement, and the corresponding detection response event and measurement information are recorded; (3) Basis filtering: All measurement ends disclose measurement basis information, retain valid response events generated under the same basis, and obtain the original bit value string of the corresponding basis according to the predefined bit mapping rules; When more than two measurement ends receive valid response events at the same time, two are randomly selected and their corresponding detection events are retained. An entangled correlation between any two measurement ends is formed by the method of subsequent selection measurement. (4) Parameter estimation: The measurement end uses an auxiliary basis to estimate parameters according to the pre-selected measurement scheme and uses a signal basis to extract the original key; (5) Post-processing: The original key string is subjected to classical error correction, error verification and privacy amplification from the first measurement end to the nth measurement end to obtain the final security key.

8. The source-device-independent quantum key distribution network method according to claim 7, characterized in that, The non-classical light source in step (1) is a quantum light source capable of generating a state with high single-photon purity, such as a single-photon source or a Schrödinger cat state.

9. The source-device-independent quantum key distribution network method according to claim 7, characterized in that, The measurement scheme can be based on time, phase, or polarization degrees of freedom; the measurement basis vector can be a time-domain basis vector, an interferometric basis vector, or a polarization basis vector, wherein the time-domain basis vector is used to perform photon detection for each time window; the interferometric basis vector is used to perform interferometric measurement on light pulses in adjacent time windows; and the polarization basis vector is used to measure the polarization state of each light pulse.

10. A system based on the source device-independent quantum key distribution network method of claim 7, characterized in that, The system includes a first transmitting end and a first measuring end to an nth measuring end. The first transmitting end includes a photon preparation module and a state distribution module. The photon preparation module is used to transmit states with high-purity single-photon components, whose second-order correlation function... The value is much smaller than 1, which approximates the degree of suppression of multiphoton components; the state distribution module is used to randomly distribute the optical pulse sequence to n measurement ends by means of optical path switching or probability beam splitting; The measurement end includes a measurement module, which is used to realize the selection of measurement basis vectors, the measurement of single-photon-level light pulses, and data recording. The first transmitting end and the first to nth measuring ends each include a post-processing module. The post-processing module is used to control each module of the local end, and to perform subsequent screening of the original key, classical error correction, error verification and privacy amplification to obtain the final key.

11. The system of the source device-independent quantum key distribution network method according to claim 10, characterized in that: The photon preparation module includes a non-classical quantum light source, which can be a single-photon source or a Schrödinger's cat state, etc., to transmit states with high-purity single-photon components. The state distribution module can include a 1×n balanced beam splitter to randomly distribute the optical pulse sequence to the first to the nth measurement end. The state distribution module can also adopt an equivalent distribution structure based on polarization states, including an optical switch matrix and a polarization beam splitter network. A polarization controller and a polarization beam splitter are used to realize the distribution of polarization states.

12. The system of the source device-independent quantum key distribution network method according to claim 10, characterized in that: The measurement module is used to randomly select measurement basis vectors in a preset measurement scheme and detect received single-photon-level light pulses. It includes an optical path beam splitting structure and measurement units corresponding to different measurement basis vectors. The optical path beam splitting structure is used to randomly select measurement basis vectors. The measurement unit may be: a time-domain measurement module, used to detect light pulses in each time window, preferably using a single-photon detector; an interferometric measurement module, used to perform interferometric measurements of light pulses in adjacent time windows, preferably using an asymmetric Mach-Zehnder interferometer structure; and a polarization measurement module, used to measure the polarization state of each light pulse, preferably using a polarization controller, a polarization beam splitter, and a single-photon detector.

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