Single-particle entangled states (SPES) can offer a more secure way of encoding and processing quantum information than their multi-particle counterparts. The SPES generated via a 2D alternate quantum-walk setup from initially separable states can be either 3-way or 2-way entangled. This letter shows that the generated genuine three-way and nonlocal two-way SPES can be used as cryptographic keys to securely encode two distinct messages simultaneously. We detail the message encryption-decryption steps and show the resilience of the 3-way and 2-way SPES-based cryptographic protocols against eavesdropper attacks like intercept-and-resend and man-in-the-middle. We also detail how these protocols can be experimentally realized using single photons, with the three degrees of freedom being OAM, path, and polarization. These have unparalleled security for quantum communication tasks. The ability to simultaneously encode two distinct messages using the generated SPES showcases the versatility and efficiency of the proposed cryptographic protocol. This capability could significantly improve the throughput of quantum communication systems.

翻译：单粒子纠缠态（SPES）相比多粒子纠缠态能提供更安全的量子信息编码与处理方式。基于二维交替量子行走装置从初始可分离态生成的SPES可呈现三路或两路纠缠特性。本文表明，生成的真三路与非局域两路SPES可作为密码密钥同时安全编码两条不同消息。我们详述消息加密-解密步骤，并展示基于三路和两路SPES的密码协议对抗截获重发及中间人攻击等窃听行为的鲁棒性。同时阐释如何利用单光子实验实现这些协议，其中涉及轨道角动量（OAM）、路径和偏振三个自由度。这些协议为量子通信任务提供了无与伦比的安全性。利用所生成SPES同时编码两条不同消息的能力，展现了所提密码协议的多功能性与高效性，该特性有望显著提升量子通信系统的吞吐量。