Dynamically prepared networked point-to-multipoint continuous variable quantum key distribution method, device and system
By employing a passive key preparation method, the problems of user isolation and high cost in networked CV-QKD systems are solved, achieving low-cost, high-performance networked key distribution without active modulation, simplifying the system structure and supporting multi-user concurrent key distribution.
Patent Information
- Application Number
- CN202511184666.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-22
- Publication Date
- 2025-12-12
AI Technical Summary
Existing networked CV-QKD systems face challenges such as difficulty in user isolation, high cost, vulnerability to modulator attacks, and nonlinear distortion, and are difficult to deploy in a high-performance, low-cost networked manner.
By employing a passive preparation method, through multi-mode thermal field state preparation, detection, excessive noise suppression, and post-processing steps, networked point-to-multipoint continuous variable quantum key distribution without active modulation is achieved, ensuring that each end user independently generates keys and optimizing network performance.
It achieves low-cost, high-performance networked key distribution without active modulation, simplifies system architecture, enhances security and scalability, and supports concurrent key distribution for multiple users.
Smart Images
Figure CN121125071A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The application belongs to the field of continuous variable quantum key distribution, and particularly relates to a networked point-to-multipoint continuous variable quantum key distribution method, device and system based on passive dynamic preparation. BACKGROUND
[0002] Quantum key distribution provides information-theoretic security by exploiting quantum mechanical laws to detect any eavesdropping activity during the key generation process. Compared with discrete variable schemes, continuous variable quantum key distribution (CV-QKD) employs coherent detection techniques and utilizes existing telecommunication components, making it highly compatible with classical optical communication systems and greatly simplifying practical implementation. In the past decade, CV-QKD technology has made significant progress: it has achieved higher system repetition rates, developed more compact integrated photonics platforms, and improved digital compensation techniques, thereby enabling secure transmission over long distances and at high code rates. In addition, the application range of CV-QKD is expanding from point-to-point links to metropolitan and even intercity networks, with the potential for large-scale network deployment.
[0003] As quantum secure communication moves beyond point-to-point links to enable large-scale deployment, networked systems become critical to cost-effective deployment. However, CV-QKD transmits keys using continuous optical fields, which essentially connects all participants, posing a serious challenge to isolating signals for each user. Existing networked theoretical schemes mainly fall into two categories: the first treats all other users as potential eavesdroppers, resulting in a key rate that tends to zero under the worst-case assumption; the second maintains a secure code rate by relying on trust in some participants, which undermines the integrity of end-to-end security. Therefore, there is a need for a more secure and high-performance networked system that can support all users in the network to generate codes independently.
[0004] In addition, existing networked deployment schemes are based on active modulation of the transmitted signal, which relies on high-speed electro-optical modulators and precise driving voltages, and is accompanied by problems such as side channels related to electro-optical modulators, attacks on modulation defects, and distortion caused by modulator nonlinearity. Furthermore, in integrated chip-based CV-QKD system platforms, the volume of the modulator is usually large, increasing the cost and difficulty of photonics integration systems.
[0005] The present application addresses the above problems by using a passive dynamic preparation method, which does not require active modulation of the signal, avoids a series of problems caused by the modulator, and removes the inherent correlation between each terminal user in the network, enabling low-cost, high-performance continuous variable quantum key distribution networks. SUMMARY
[0006] The application provides a networked point-to-multipoint continuous variable quantum key distribution method, device and system based on passive preparation, which does not need to actively modulate the transmitted signal and can enable all users in the network to independently generate keys at the same time, simplifies the system structure and realizes complete end-to-end secure key distribution and higher security code rate.
[0007] The application provides a networked point-to-multipoint continuous variable quantum key distribution method based on passive preparation.
[0008] The multi-mode thermal field state preparation step: first, the central node uses an amplified spontaneous emission source to prepare an initial thermal field state, and then the initial thermal field state is expanded into a multi-mode thermal field state by a trusted beam splitter array, which includes a first trusted beam splitter and a second trusted beam splitter; the first trusted beam splitter decomposes the initial thermal field state into a high-power thermal field state and a low-power thermal field state according to a first splitting ratio, the high-power thermal field state is heterodyne detected by a local detector of the central node to obtain a regular component measurement result of the high-power thermal field state signal as the central node original key data; the low-power thermal field state is 1 divided by n divided by the second trusted beam splitter after passing through an attenuator, and n-mode to-be-transmitted thermal field state signals are obtained; n is an integer greater than or equal to 2, and is equal to the maximum number of terminal users designed in the network; the preparation process of the n-mode to-be-transmitted thermal field state signals does not involve a modulator, so it is called passive preparation.
[0009] The detection step: assuming that the number of online users in the network is n, each mode of the n-mode to-be-transmitted thermal field state signals is sent to n terminal users after passing through n untrusted fiber channels to obtain n terminal user to-be-measured signals, and the n terminal users perform homodyne or heterodyne detection on the n terminal user to-be-measured signals to obtain n terminal user original key data corresponding to the central node original key data. Since the original key data of the terminal users is evolved from the original key data of the central node, the original key data of the terminal users has inherent correlation.
[0010] The excess noise suppression step: the n terminal user original key data is subjected to data processing, damage compensation, noise suppression and other steps to obtain n terminal user optimized key data.
[0011] The post-processing step: the n terminal users and the central node perform parameter estimation, data negotiation and security enhancement operations to remove the correlation between the terminal user original key data, and based on the terminal user optimized key data and the central node original key data, n pairs of mutually independent final keys are generated between the central node and each terminal user to realize multi-user concurrent quantum key distribution from the central node to the terminal users.
[0012] In the multi-mode thermal field state preparation step, the multi-mode thermal field state preparation can be dynamically optimized according to the number of online terminal users of the network, so as to ensure that the global performance of the network is optimal in real time: assuming that the number of online terminal users of the network is m, m is an integer not higher than n, at this time, the center node generates an m-mode to-be-transmitted thermal field state signal by discarding n-m modes in the n-mode to-be-transmitted thermal field state signal; further, the center node selects m pieces of untrusted fiber channels, and optimizes the initial thermal field state power according to the number m of online terminal users and the m pieces of untrusted fiber channels, so that the equivalent modulation variance is at an optimal value, and the maximization of the sum of the key generation rates of the m terminal users is realized.
[0013] The multi-mode thermal field state preparation step has a variant form, which is characterized in that: the center node uses the amplified spontaneous emission source to prepare an initial thermal field state, and then decomposes the initial thermal field state into a high-power thermal field state and a low-power thermal field state according to a first splitting ratio; the high-power thermal field state is heterodyne detected by a local detector of the center node to obtain a regular component measurement result of the high-power thermal field state signal as original key data of the center node; and the low-power thermal field state passes through an attenuator to obtain a to-be-transmitted thermal field state signal.
[0014] The detection step corresponding to the variant form of the above multi-mode thermal field state preparation step is: the to-be-transmitted thermal field state signal passes through an untrusted fiber channel to obtain a first broadcast signal; the first broadcast signal is split by an untrusted beam splitter array according to a second splitting ratio to obtain an n-mode second broadcast signal; each mode in the n-mode second broadcast signal is sent to an n-terminal user through an untrusted fiber channel to obtain an n-terminal user to-be-measured data signal; and the n-terminal user to-be-measured data signal is zero or heterodyne detected by the n-terminal user to obtain n-terminal user original key data corresponding to the original key data of the center node.
[0015] In the post-processing step, the final key data has the following characteristics: the key data of all terminal users is generated in parallel, that is, each quantum state preparation of the center node can support the generation of keys for all terminal users in parallel; and the key data of all terminal users is independent of each other, that is, for any terminal user, even if a third-party eavesdropper obtains the terminal user original key data of the remaining n-1 terminal users, the security of the final key data of the terminal user will not be affected.
[0016] The application provides a networked point-to-multipoint continuous variable quantum key distribution device based on passive preparation, which is characterized by comprising:
[0017] A multi-mode thermal field state preparation device includes an amplified spontaneous emission (ASE) source, a band-pass filter, a polarizer, a central node local laser, a central node heterodyne detector and a trusted beam splitter array. The ASE source can passively prepare an initial thermal field state. The band-pass filter filters the initial thermal field state to obtain a narrow-band thermal field state. The polarizer polarizes the narrow-band thermal field state to obtain a linearly polarized narrow-band thermal field state. The central node local laser provides a central node local light. The trusted beam splitter array includes a first trusted beam splitter and a second trusted beam splitter. The first trusted beam splitter is a 1-to-2 beam splitter. The second trusted beam splitter is a 1-to-n beam splitter. The first trusted beam splitter divides the linearly polarized narrow-band thermal field state into a high-power thermal field state and a low-power thermal field state according to a first splitting ratio. The central node heterodyne detector interferes the high-power thermal field state with the local light and obtains two canonical component measurements of the high-power thermal field state. The second trusted beam splitter divides the low-power thermal field state into n-mode to-be-transmitted thermal field state signals according to a second splitting ratio. n is an integer greater than or equal to 2.
[0018] An optical fiber channel includes n untrusted free optical fibers. Each untrusted free optical fiber transmits one mode of the n-mode to-be-transmitted thermal field state signals to obtain n terminal user to-be-measured signals.
[0019] A receiving device includes n terminal users. Each terminal user includes a terminal user local laser, a terminal user homodyne detector or a terminal user heterodyne detector. The terminal user local laser provides a terminal user local light. The terminal user homodyne detector or the terminal user heterodyne detector detects interference light between a terminal user to-be-measured signal and the terminal user local light.
[0020] The multi-mode thermal field state preparation device has a variant form. The variant form includes an amplified spontaneous emission (ASE) source, a band-pass filter, a polarizer, a central node local laser, a central node heterodyne detector and a 1-to-2 trusted uniform beam splitter. The ASE source can passively prepare an initial thermal field state. The band-pass filter polarizes the initial thermal field state to obtain a narrow-band thermal field state. The polarizer polarizes the narrow-band thermal field state to obtain a linearly polarized narrow-band thermal field state. The central node local laser provides a central node local light. The 1-to-2 trusted uniform beam splitter divides the linearly polarized narrow-band thermal field state into a central node first thermal field state and a central node second thermal field state. The heterodyne detector detects interference light between the central node first thermal field state and the central node local light.
[0021] The variant of the multi-mode thermal field state preparation device corresponds to an optical fiber channel comprising one primary untrusted optical fiber, an untrusted beam splitter array, and n secondary untrusted optical fibers; the second thermal field state of the central node is transmitted through the primary untrusted optical fiber to obtain a beam splitting node signal; the untrusted beam splitter array is a 1-to-n beam splitter, which divides the beam splitting node signal into n post-beam splitting signals according to a second beam splitting ratio, and the n secondary untrusted optical fibers respectively transmit n modes of the n post-beam splitting signals to obtain n terminal user to-be-tested signals.
[0022] When the number of terminal users is m and m is less than n, the untrusted beam splitter array is a 1-to-n beam splitter, and m of the n output modes are respectively transmitted to m terminal users through m secondary untrusted optical fibers; alternatively, an untrusted beam splitter array based on a 1-to-m beam splitter can also be used, and the m output modes are respectively transmitted to the m terminal users through the m secondary untrusted optical fibers.
[0023] The application provides a networked point-to-multipoint continuous variable quantum key distribution system based on dynamically prepared network nodes, characterized by comprising:
[0024] The central node: when the number of online terminal users in the network is equal to the maximum capacity n of network users, the central node uses a multi-mode thermal field state preparation device to prepare n-mode to-be-transmitted thermal field state signals, and transmits the n-mode to-be-transmitted thermal field state signals to n untrusted optical fiber channels for transmission; when the number of online terminal users in the network is equal to m and less than the maximum capacity n of network users, the central node uses a multi-mode thermal field state preparation device to prepare m-mode to-be-transmitted thermal field state signals, optimizes the initial thermal field state preparation to ensure the optimal global network performance, and then transmits the m-mode to-be-transmitted thermal field state signals to m untrusted optical fiber channels for transmission; when the number of online terminal users in the network changes from m to m', if m' is greater than m, the central node reduces and discards.
[0025] The terminal user: the number of terminal users is n, and the n terminal users all use a receiving device to receive and detect n terminal user to-be-tested signals to obtain n terminal user original key data.
[0026] The excess noise suppression unit: the excess noise suppression unit processes the n terminal user original key data through data processing, damage compensation, noise compression, and the like to obtain n terminal user optimized key data, and improves the signal-to-noise ratio parameter of the continuous variable quantum key distribution system.
[0027] The post-processing unit performs parameter estimation, data error correction and privacy enhancement operation on the optimized key data of the n terminal users and the key data of the central node, and generates n pairs of final key data independent of each other between the central node and the terminal users, thereby realizing quantum key distribution service from the central node to the terminal users.
[0028] The beneficial effects of the present application are as follows:
[0029] (1) The networked point-to-multipoint continuous variable quantum key distribution method, device and system based on passive preparation can simplify the signal preparation process of the central node by using the passive preparation method without active modulation of the transmitted signal, avoiding problems such as side channel related to electro-optical modulator, attack on modulation defects, and distortion caused by modulator nonlinearity.
[0030] (2) The networked point-to-multipoint continuous variable quantum key distribution method, device and system based on passive preparation can dynamically adjust the network capacity and ensure the optimal global key generation rate without changing the actual network deployment facilities.
[0031] (3) The networked point-to-multipoint continuous variable quantum key distribution method, device and system based on passive preparation can enable all terminal users to generate key data in parallel and independently, thereby maximizing the security of the terminal user key data.
[0032] (4) The networked point-to-multipoint continuous variable quantum key distribution method, device and system based on passive preparation simplifies the signal source preparation method, is conducive to low-cost miniaturized chip integration, greatly enhances the scalability of the system, and realizes simple, efficient and large-scale networked quantum key distribution. BRIEF DESCRIPTION OF DRAWINGS
[0033] Figure 1 A networked point-to-multipoint continuous variable quantum key distribution system based on passive preparation of the present application is shown in the figure;
[0034] Figure 2 A networked point-to-multipoint continuous variable quantum key distribution method based on passive preparation of the present application is shown in the figure;
[0035] Figure 3 A networked point-to-multipoint continuous variable quantum key distribution device based on passive preparation of the present application is shown in the figure;
[0036] Figure 4 A networked point-to-multipoint continuous variable quantum key distribution method based on passive preparation of the present application is shown in the figure;
[0037] Figure 5Fig. 2 is a schematic diagram of a networked point-to-multipoint continuous variable quantum key distribution device based on dynamically prepared networked nodes. DETAILED DESCRIPTION
[0038] For the convenience of those skilled in the art to understand and implement the present application, the present application will be described in more detail below in conjunction with the drawings and examples. Obviously, the described examples are only partial examples of the present application, and not all examples. Based on the examples in the present application, all other examples obtained by those skilled in the art without creative labor should fall within the scope of the present application.
[0039] The present application provides a networked point-to-multipoint continuous variable quantum key distribution method, device and system based on dynamically prepared networked nodes, which can realize a fully passive key distribution network, and each terminal user in the network can be parallel and independent code, simplifying the network structure, improving the network performance, and being beneficial to the low-cost miniaturized photonic integrated quantum key distribution network system.
[0040] The networked point-to-multipoint continuous variable quantum key distribution system based on dynamically prepared networked nodes has a system structure as shown in Figure 1 The center node, n terminal users, an excess noise suppression unit and a post-processing unit.
[0041] When the number of online terminal users in the network is equal to the maximum capacity n of the network users, the center node uses a multi-mode thermal field state preparation device to prepare n-mode to-be-transmitted thermal field state signals, and sends the n-mode to-be-transmitted thermal field state signals to n untrusted optical fiber channels for transmission; when the number of online terminal users in the network is equal to m and less than the maximum capacity n of the network users, the center node uses a multi-mode thermal field state preparation device to prepare m-mode to-be-transmitted thermal field state signals, and optimizes the initial thermal field state preparation to ensure the optimal global network performance, and then sends the m-mode to-be-transmitted thermal field state signals to m untrusted optical fiber channels for transmission; when the number of online terminal users in the network changes from m to m', if m' is greater than m, the center node reduces and discards.
[0042] The number of terminal users is n, and each of the n terminal users uses a receiving device to receive and detect n terminal user to-be-tested signals to obtain n terminal user original key data.
[0043] The excess noise suppression unit performs data processing, damage compensation, noise compression and other steps on the n terminal user original key data to obtain n terminal user optimized key data, thereby improving the signal-to-noise ratio parameter of the continuous variable quantum key distribution system.
[0044] The post-processing unit performs parameter estimation, data error correction and privacy enhancement operation on the n pairs of final key data between the central node and the terminal users after optimizing the key data of the n terminal users and the key data of the central node, to generate n pairs of final key data independent of each other, thereby realizing quantum key distribution service from the central node to the terminal users.
[0045] Specifically, the networked point-to-multipoint continuous variable quantum key system based on dynamic preparation has two implementation methods. The networked point-to-multipoint continuous variable quantum key distribution method based on dynamic preparation and the corresponding device will be described below with reference to the accompanying drawings.
[0046] Embodiment 1
[0047] The first key distribution method of the networked point-to-multipoint continuous variable quantum key method has a flowchart as shown in Figure 2 The specific steps are as follows:
[0048] Multi-mode thermal field state preparation step: first, the central node uses an amplified spontaneous emission source to prepare an initial thermal field state, and then the initial thermal field state is expanded into a multi-mode thermal field state by a trusted beam splitter array, which includes a first trusted beam splitter and a second trusted beam splitter; the first trusted beam splitter decomposes the initial thermal field state into a high-power thermal field state and a low-power thermal field state according to a first splitting ratio, the high-power thermal field state is heterodyne detected by a local detector of the central node to obtain a regular component measurement result of the high-power thermal field state signal as the original key data of the central node; the low-power thermal field state is attenuated by an attenuator and then split by the second trusted beam splitter according to a second splitting ratio to obtain n-mode to-be-transmitted thermal field state signals; n is the maximum number of terminal users designed in the network. In this step, the multi-mode thermal field state preparation can be dynamically optimized according to the number of online terminal users in the network, so as to ensure that the global performance of the network is real-time optimal: assuming that the number of online terminal users in the network is m, m is an integer not higher than n, at this time the central node generates m-mode to-be-transmitted thermal field state signals by discarding n-m modes of the n-mode to-be-transmitted thermal field state signals; further, the central node selects m untrusted optical fiber channels, and optimizes the initial thermal field state power according to the number of online terminal users m and the m untrusted optical fiber channels, so that the equivalent modulation variance is at an optimal value, thereby maximizing the sum of the key generation rates of the m terminal users.
[0049] The detection step: assuming that the number of online users of the network is n, each mode of the n-mode to-be-transmitted thermal field state signal is sent to n terminal users after passing through n untrusted optical fiber channels to obtain n terminal user to-be-tested signals, and the n terminal users perform homodyne or heterodyne detection on the n terminal user to-be-tested signals to obtain n terminal user original key data corresponding to the center node original key data. Since the terminal user original key data is evolved from the center node original key data, the terminal user original key data between the terminal users has an inherent correlation.
[0050] The excess noise suppression step: the n terminal user original key data is subjected to data processing, damage compensation, noise suppression and other steps to obtain n terminal user optimized key data.
[0051] The post-processing step: the n terminal users respectively perform parameter estimation, data negotiation and security enhancement operations with the center node, remove the correlation between the terminal user original key data, and based on the terminal user optimized key data and the center node original key data, generate n pairs of mutually independent final keys between the center node and each terminal user, and realize multi-user concurrent quantum key distribution from the center node to the terminal users. After the post-processing step is completed, the final key data has the following characteristics: the key data of all terminal users is generated in parallel, that is, each quantum state preparation of the center node can support all terminal users to generate keys in parallel; the key data of all terminal users is independent of each other, that is, for any terminal user, even if a third-party eavesdropper obtains the terminal user original key data of the remaining n-1 terminal users, the security of the final key data of the terminal user will not be affected.
[0052] Figure 3 A device schematic diagram for the networked point-to-multipoint continuous variable quantum key distribution method based on passive dynamic preparation provided for the embodiments of the present application is as follows:
[0053] The multi-mode thermal field state preparation device comprises an amplified spontaneous emission (ASE) source, a band-pass filter, a polarizer, a central node local oscillator, a central node heterodyne detector and a trusted beam splitter array; the amplified spontaneous emission source can passively prepare an initial thermal field state, the band-pass filter filters the initial thermal field state to obtain a narrow-band thermal field state, the polarizer polarizes the narrow-band thermal field state to obtain a linearly polarized narrow-band thermal field state, the central node local oscillator provides a central node local light, the trusted beam splitter array comprises a first trusted beam splitter and a second trusted beam splitter, the first trusted beam splitter is a 1:2 beam splitter, and the second trusted beam splitter is a 1:n beam splitter; the first trusted beam splitter divides the linearly polarized narrow-band thermal field state into a high-power thermal field state and a low-power thermal field state according to a first splitting ratio, the central node heterodyne detector interferes the high-power thermal field state with the local light, and two canonical component measurement results of the high-power thermal field state are obtained; the second trusted beam splitter divides the low-power thermal field state into n-mode to-be-transmitted thermal field state signals according to a second splitting ratio; wherein n is an integer greater than or equal to 2.
[0054] The fiber channel comprises n untrusted free optical fibers, each of which transmits one mode of the n-mode to-be-transmitted thermal field state signals to obtain n terminal user to-be-measured signals.
[0055] The receiving device comprises n terminal users, each of which comprises a terminal user local oscillator and a terminal user homodyne detector or a terminal user heterodyne detector; the terminal user local oscillator provides terminal user local light, and the terminal user homodyne detector or the terminal user heterodyne detector detects interference light of the terminal user to-be-measured signal and the terminal user local light.
[0056] Embodiment 2:
[0057] The first key distribution method of the networked point-to-multipoint continuous variable quantum key method based on passive preparation is as shown in Figure 4 The specific steps are as follows:
[0058] Multi-mode thermal field state preparation step: the center node uses the amplified spontaneous emission source to prepare an initial thermal field state, and then decomposes the initial thermal field state into a high-power thermal field state and a low-power thermal field state according to a first splitting ratio. The high-power thermal field state is heterodyne detected by a local detector of the center node to obtain a regular component measurement result of a high-power thermal field state signal, which is used as original key data of the center node. The low-power thermal field state passes through an attenuator to obtain a to-be-transmitted thermal field state signal. This step can dynamically optimize the preparation of the multi-mode thermal field state according to the number of online terminal users of the network, thereby ensuring that the global performance of the network is real-time optimal. Assuming that the number of online terminal users of the network is m, m is an integer not higher than n, and the center node generates an m-mode to-be-transmitted thermal field state signal by discarding n-m modes in the n-mode to-be-transmitted thermal field state signal. Further, the center node selects m pieces of untrusted fiber channels, and optimizes the initial thermal field state power according to the number m of online terminal users and the m pieces of untrusted fiber channels, so that the equivalent modulation variance is at an optimal value, and the sum of the key generation rates of the m terminal users is maximized.
[0059] Detection step: assuming that the number of online users of the network is n, the n-mode to-be-transmitted thermal field state signal passes through an untrusted fiber channel to obtain a first broadcast signal. The first broadcast signal is split by an untrusted beam splitter array according to a second splitting ratio to obtain an n-mode second broadcast signal. Each mode in the n-mode second broadcast signal is sent to an n-mode terminal user through an untrusted fiber channel to obtain an n-mode terminal user to-be-measured data signal. The n-mode terminal user to-be-measured data signal is homodyne or heterodyne detected by the n-mode terminal user to obtain n-mode terminal user original key data corresponding to the original key data of the center node.
[0060] Excess noise suppression step: the n-mode terminal user original key data passes through steps such as data processing, damage compensation, and noise suppression to obtain n-mode terminal user optimized key data.
[0061] Post-processing step: the n-mode terminal user and the center node perform parameter estimation, data negotiation, and security enhancement operations, respectively, to remove the correlation between the terminal user original key data. Based on the terminal user optimized key data and the original key data of the center node, n pairs of mutually independent final keys are generated between the center node and each terminal user, and multi-user concurrent quantum key distribution from the center node to the terminal user is realized.
[0062] Figure 5 A device diagram for the networked point-to-multipoint continuous variable quantum key distribution method based on passive dynamic preparation provided by the embodiments of the present application is as follows:
[0063] The multi-mode thermal field state preparation device comprises an amplified spontaneous emission (ASE) source, a band-pass filter, a polarizer, a center node local oscillator, a center node heterodyne detector and a 1 / 2 trusted uniform beam splitter. The ASE source can passively prepare an initial thermal field state, the band-pass filter polarizes the initial thermal field state to obtain a narrow-band thermal field state, the polarizer polarizes the narrow-band thermal field state to obtain a linearly polarized narrow-band thermal field state, the center node local oscillator provides a center node local light, the 1 / 2 trusted uniform beam splitter divides the linearly polarized narrow-band thermal field state into a center node first thermal field state and a center node second thermal field state, and the heterodyne detector detects interference light of the center node first thermal field state and the center node local light.
[0064] The fiber channel comprises one primary untrusted optical fiber, an untrusted beam splitter array and n secondary untrusted optical fibers; the center node second thermal field state is transmitted through the primary untrusted optical fiber to obtain a beam splitting node signal; the untrusted beam splitter array is a 1 / n beam splitter, which divides the beam splitting node signal into n beam-splitting signals according to a second splitting ratio, and the n secondary untrusted optical fibers respectively transmit n modes of the n beam-splitting signals to obtain n terminal user to-be-tested signals. In this scenario, the broadcast channel is set as follows: when the number of terminal users is m and m is less than n, the untrusted beam splitter array is a 1 / n beam splitter, and m of the n output modes are respectively transmitted to m terminal users through m secondary untrusted optical fibers; alternatively, an untrusted beam splitter array based on a 1 / m beam splitter can also be used, and m output modes are respectively transmitted to m terminal users through m secondary untrusted optical fibers.
[0065] The receiving device comprises n terminal users, each of which comprises a terminal user local oscillator, a terminal user homodyne detector or a terminal user heterodyne detector; the terminal user local oscillator provides terminal user local light, and the terminal user homodyne detector or the terminal user heterodyne detector detects interference light of the terminal user to-be-tested signal and the terminal user local light.
Claims
1. A method for networked point-to-multipoint continuous-variable quantum key distribution based on dynamically prepared networked points, characterized in that, Includes the following steps: Multi-mode thermal field state preparation steps: The central node prepares an initial thermal field state using an amplified spontaneous emission source. This initial thermal field state is then expanded into a multi-mode thermal field state by a trusted beamsplitter array, which includes a first trusted beamsplitter and a second trusted beamsplitter. The first trusted beamsplitter decomposes the initial thermal field state into a high-power thermal field state and a low-power thermal field state according to a first splitting ratio. The high-power thermal field state is heterodyne-detected by the central node's local detector to obtain the regular component measurement result of the high-power thermal field state signal, which serves as the central node's original key data. The low-power thermal field state, after passing through an attenuator, is split into n beams by the second trusted beamsplitter according to a second splitting ratio, resulting in an n-mode thermal field state signal to be transmitted. Here, n is an integer greater than or equal to 2, equal to the maximum number of terminal users connected in the network design. The preparation process of the n-mode thermal field state signal to be transmitted does not involve a modulator, hence it is called passively prepared. Detection steps: Assuming there are n online users, each mode of the n-mode thermal field signal to be transmitted is sent to n terminal users through n untrusted optical fiber channels, resulting in n terminal user test signals. The n terminal users then perform homodyne or heterodyne detection on these n terminal user test signals to obtain n terminal user original key data corresponding to the original key data of the central node. Since the original key data of the terminal users all evolve from the original key data of the central node, there is an inherent correlation between the original key data of each terminal user. Excessive noise suppression step: The original key data of the n terminal users are processed through data processing, impairment compensation, noise suppression and other steps to obtain optimized key data of the n terminal users. Post-processing steps: The n terminal users respectively perform parameter estimation, data negotiation, and security enhancement operations with the central node to remove the association between the original key data of the terminal users, and generate n pairs of independent final keys between the central node and each terminal user based on the optimized key data of the terminal users and the original key data of the central node, so as to realize multi-user concurrent quantum key distribution from the central node to the terminal users.
2. The multi-mode thermal field state preparation step according to claim 1, characterized in that, The preparation of multi-mode thermal field states can be dynamically optimized based on the number of online terminal users, thereby ensuring the real-time optimal global performance of the network: Assuming the number of online terminal users is m, where m is an integer not higher than n, the central node generates m-mode thermal field state signals by discarding nm modes from the n-mode thermal field state signals to be transmitted; furthermore, the central node selects m untrusted optical fiber channels and optimizes their initial thermal field state power according to the number of online terminal users m and the situation of m untrusted optical fiber channels, so that the equivalent modulation variance is at the optimal value, thereby maximizing the sum of the key generation rates of m terminal users.
3. The post-processing step according to claim 1, wherein the final key data is characterized by: key data of all terminal users being generated in parallel, that is, each quantum state preparation of the central node can support all terminal users and generate keys in parallel; key data of all terminal users being independent of each other, that is, for any terminal user, even if a third-party eavesdropper obtains the original key data of the other n-1 terminal users, it will not affect the security of its final key data.
4. A dynamically prepared networked point-to-multipoint continuous variable quantum key distribution device, characterized in that, include: Multimode thermal field state preparation device: including amplified spontaneous emission source, bandpass filter, polarizer, central node local oscillator laser, central node heterodyne detector and reliable beam splitter array; The amplified spontaneous emission source can passively prepare the initial thermal field state. The bandpass filter filters the initial thermal field state to obtain a narrowband thermal field state. The polarizer polarizes the narrowband thermal field state to obtain a linearly polarized narrowband thermal field state. The central node local oscillator laser provides the central node local oscillator light. The reliable beamsplitter array includes a first reliable beamsplitter and a second reliable beamsplitter. The first reliable beamsplitter is a 1-to-2 beamsplitter, and the second reliable beamsplitter is a 1-to-n beamsplitter. The first reliable beamsplitter divides the linearly polarized narrowband thermal field state into a high-power thermal field state and a low-power thermal field state according to a first beamsplitter ratio. The central node heterodyne detector interferes with the high-power thermal field state and the local oscillator light, and obtains the measurement results of the two canonical components of the high-power thermal field state. The second reliable beamsplitter divides the low-power thermal field state into an n-mode thermal field state signal to be transmitted according to a second beamsplitter ratio. The n is an integer greater than or equal to 2. Fiber optic channel: includes n untrusted free optical fibers, each of which transmits one mode of the n-mode thermal field state signal to be transmitted, resulting in n end-user test signals. Receiving device: includes n terminal users, each terminal user including a terminal user local oscillator laser, a terminal user homodyne detector or a terminal user heterodyne detector; the terminal user local oscillator laser provides terminal user local oscillator light, and the terminal user homodyne detector or the terminal user heterodyne detector detects the interference light between the terminal user signal to be measured and the terminal user local oscillator light.
5. A dynamically prepared networked point-to-multipoint continuous-variable quantum key distribution system, characterized in that, include: Central Node: When the number of online terminal users in the network equals the maximum network user capacity n, the central node uses the multi-mode thermal field state preparation device to prepare the n-mode thermal field state signal to be transmitted, and sends the n-mode thermal field state signal to be transmitted to n untrusted optical fiber channels for transmission; when the number of online terminal users in the network is equal to m and less than the maximum network user capacity n, the central node uses the multi-mode thermal field state preparation device to prepare the m-mode thermal field state signal to be transmitted, optimizes the initial thermal field state preparation to ensure optimal global network performance, and then sends the m-mode thermal field state signal to be transmitted to m untrusted optical fiber channels for transmission; when the number of online terminal users in the network changes from m to m', if m' is greater than m, the central node reduces the number of discarded users. End users: The number of end users is n. Each of the n end users uses the receiving device to receive and detect the signals to be tested from the n end users to obtain the original key data of the n end users. Excessive noise suppression unit: The excessive noise suppression unit performs data processing, impairment compensation, noise compression and other steps on the original key data of the n terminal users to obtain optimized key data of the n terminal users, thereby improving the signal-to-noise ratio parameter of the continuous variable quantum key distribution system. Post-processing unit: The post-processing unit simultaneously performs parameter estimation, data error correction, and security enhancement operations on the optimized key data of the n end users and the key data of the central node. Then, it generates n pairs of independent final key data between the central node and each end user, realizing quantum key distribution service from the central node to the end users.