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Chinese Science Bulletin (Chinese Version)

High-capacity quantum secure direct communication scheme based on practical light sources

Jiawei Ying, Shipu Gu, Yanyan Zheng, Xingfu Wang, Lan Zhou, Yubo Sheng, Hesheng Chen

Published Jun 1, 2026• 0 citations

Abstract

量子安全直接通信(QSDC)可以通过量子信道直接传输机密信息，具有广阔的应用前景。其中，基于单光子的QSDC方案由于不依赖纠缠资源，实现难度低，是最接近实用化的QSDC方案之一。但是，传统的QSDC方案在抵御窃听者攻击时，通常采用X基和Z基进行安全性检测，这会放宽对窃听者的限制，导致方案安全信息容量和最大传输距离降低。为此，本文提出了一个高容量的QSDC方案，将Y基安全性检测引入分析。通过构建系统模型，本文分析了采用弱相干脉冲源和预示单光子源时方案的性能，并通过参数优化，使方案在各信道衰减条件下均达到最优性能。结果表明，在强度最优时，基于弱相干脉冲源与预示单光子源方案的最大可容忍信道衰减分别为 11.25 dB 和 12.1 dB。在损耗系数为 0.2 dB/km 的光纤信道中，其对应的最大通信距离分别为28.125 km和30.25 km，较传统方案分别提升了 57.3% 和 69.2%。在信道衰减为2、4、6 dB时，基于预示单光子源的方案单位脉冲的安全信息容量分别达到传统方案的7.69、17.94和94.79倍，显著提升了系统的安全通信性能。

DOI: 10.1360/csb-2026-0367

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量子安全直接通信(QSDC)可以通过量子信道直接传输机密信息，具有广阔的应用前景。其中，基于单光子的QSDC方案由于不依赖纠缠资源，实现难度低，是最接近实用化的QSDC方案之一。但是，传统的QSDC方案在抵御窃听者攻击时，通常采用X基和Z基进行安全性检测，这会放宽对窃听者的限制，导致方案安全信息容量和最大传输距离降低。为此，本文提出了一个高容量的QSDC方案，将Y基安全性检测引入分析。通过构建系统模型，本文分析了采用弱相干脉冲源和预示单光子源时方案的性能，并通过参数优化，使方案在各信道衰减条件下均达到最优性能。结果表明，在强度最优时，基于弱相干脉冲源与预示单光子源方案的最大可容忍信道衰减分别为 11.25 dB 和 12.1 dB。在损耗系数为 0.2 dB/km 的光纤信道中，其对应的最大通信距离分别为28.125 km和30.25 km，较传统方案分别提升了 57.3% 和 69.2%。在信道衰减为2、4、6 dB时，基于预示单光子源的方案单位脉冲的安全信息容量分别达到传统方案的7.69、17.94和94.79倍，显著提升了系统的安全通信性能。

量子安全直接通信（quantum secure direct communication, QSDC）可通过量子信道直接传输秘密信息。受控量子安全直接通信（controlled quantum secure direct communication, CQSDC）加入了第三方对通信的控制，能够有效提高通信过程的安全性，受到广泛研究。之前的CQSDC方案大多需要多光子GHZ态纠缠源，在现有实验条件下该光源制备存在严重挑战。而且，之前的CQSDC方案需要三轮光子传输和安全性检测，对量子资源消耗较大，导致信息传输效率较低。本文提出一种基于两组贝尔基的CQSDC方案。控制方随机选择两组贝尔基制备大量双光子贝尔态纠缠对，通过量子信道分发给通信双方，通信双方先经过安全性检测确保信道无窃听，随后信息发送方编码量子态发送信息，接收方在控制方的协助下才能解码，获取信息。该方法只需要使用贝尔态进行通信，并且仅需两轮光子传输和两轮安全性检测，可以降低方案的实现复杂性，减少量子资源消耗以及多轮光子传输的损耗，在未来远距离量子通信领域具有重要的应用。

量子安全直接通信（Quantum secure direct communication,QSDC）协议是继BB84和EPR协议之后提出的关于量子通信的一个重要协议。自2000年龙桂鲁和刘晓曙提出第一个QSDC协议以来,得到了迅速发展。随后,邓富国等利用块传输思想,提出了基于EPR对的Two-Step QSDC方案。研究提出了光子的制备、光子通过偏振片前后的变化等算法,利用AS代码将量子通信过程中一些不可观察的过程可视化,并以Flash技术为载体,对基于EPR对的Two-Step QSDC方案进行了模拟仿真。模拟结果在直观展示出通信过程的基础上,证明了利用计算机对量子通信进行仿真的可行性。

摘要: 为了提高量子安全直接通信协议的安全性并同时降低其成本，该文通过对协议中检测窃听过程的分析给出了一种有效的方法，并从量子安全直接通信和量子秘密共享两种角度验证了这种方法的可行性。合法通信者使用携带有秘密消息的传输粒子检测窃听，并且不会泄露任何秘密消息。分析表明，合法通信者在不用制备单独用来检测窃听的检测粒子情况下，不仅能够让协议的量子比特理论效率达到100%，而且可以确保其无条件安全。关键词: 量子安全直接通信 / 传输粒子 / 检测粒子 / 量子比特理论效率

In practical quantum communication, imperfect devices may introduce side channels, creating opportunities for eavesdroppers. Especially on the source side, the side channels created by active modulation may compromise the security of the protocol. We proposes a passively-sourced quantum secure direct communication (QSDC) protocol based on fully passive source. By passively modulating both the quantum state and the intensity of the decoy state, we can avoid active modulation operations at the source, thereby enhancing the robustness of QSDC against side-channel attacks. We developed a system model and conducted parameter optimization to obtain the maximum secrecy message transmission rate achievable by the protocol for each channel attenuation. At a channel attenuation of 2, 4, 6 dB (corresponding to a communication distance of 5, 10, 15 km), the secrecy message transmission rates are 5.76 * 10^-5, 9.92 * 10^-6, and 4.99 * 10^-7 bit/sec. And its maximum communication distance is about 16.875 km, which is about 94.4% of that of actively modulated QSDC.

Abstract Quantum secure direct communication (QSDC) promises unconditional security for direct information transmission without pre-shared keys. However, practical implementations using weak coherent sources face critical challenges from device imperfections, such as emitting vacuum states and multiphoton states. Here, we introduce a heralded QSDC protocol leveraging squeezed-state superposition in a cross-Kerr nonlinear medium, where single-mode squeezed states interfere with coherent states to generate superposition states via post-measurement selection. We have considered three detector models to analyze the heralding performance of light sources under different conditions, including the ideal photon number detector, the practical photon number detector, and the practical photon detector. Our proposed protocol dramatically reduces the vacuum state ratio compared to weak coherent pulse sources, and the multiphoton ratio is still maintained at a low level, significantly enhancing the security information capacity and the maximum secure communication distance. We perform numerical simulations and compare our protocol with the optical single-photon-based QSDC protocol. At 7.5 km with an average photon number of 0.01, the security information capacity improves by 13.42 times, 12.20 times, and 8.64 times for three detector models. Extending to 17.5 km, these gains will be to 277.59 times, 251.58 times, and 172.91 times. Our work provides a robust framework for high-capacity, long-distance, secure quantum communication systems. PACS numbers: 03.67.Pp, 03.67.Hk, 03.65.Ud