Quantum key distribution, which allows two distant parties to share an unconditionally secure cryptographic key, promises to play an important role in the future of communication. For this reason such technique has attracted many theoretical and experimental efforts, thus becoming one of the most prominent quantum technologies of the last decades. The security of the key relies on quantum mechanics and therefore requires the users to be capable of performing quantum operations, such as state preparation or measurements in multiple bases. A natural question is whether and to what extent these requirements can be relaxed and the quantum capabilities of the users reduced. Here we demonstrate a novel quantum key distribution scheme, where users are fully classical. In our protocol, the quantum operations are performed by an untrusted third party acting as a server, which gives the users access to a superimposed single photon, and the key exchange is achieved via interaction-free measurements on the shared state. We also provide a full security proof of the protocol by computing the secret key rate in the realistic scenario of finite-resources, as well as practical experimental conditions of imperfect photon source and detectors. Our approach deepens the understanding of the fundamental principles underlying quantum key distribution and, at the same time, opens up new interesting possibilities for quantum cryptography networks

中文翻译：

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经典用户的实验性半量子密钥分配

量子密钥分发允许两个远程方共享无条件安全的加密密钥，有望在未来的通信中发挥重要作用。出于这个原因，这种技术吸引了许多理论和实验的努力，从而成为过去几十年最突出的量子技术之一。密钥的安全性依赖于量子力学，因此要求用户能够执行量子操作，例如状态准备或多基测量。一个自然的问题是这些要求是否可以放宽以及在多大程度上可以放宽用户的量子能力。在这里，我们展示了一种新颖的量子密钥分配方案，其中用户是完全经典的。在我们的协议中，量子操作由充当服务器的不受信任的第三方执行，这使用户可以访问叠加的单个光子，并且通过对共享状态的无交互测量来实现密钥交换。我们还通过计算有限资源现实场景中的密钥率以及不完美光子源和探测器的实际实验条件，为协议提供了完整的安全证明。我们的方法加深了对量子密钥分发的基本原理的理解，同时为量子密码网络开辟了新的有趣可能性 我们还通过计算有限资源现实场景中的密钥率以及不完美光子源和探测器的实际实验条件，为协议提供了完整的安全证明。我们的方法加深了对量子密钥分发的基本原理的理解，同时为量子密码网络开辟了新的有趣可能性 我们还通过计算有限资源现实场景中的密钥率以及不完美光子源和探测器的实际实验条件，为协议提供了完整的安全证明。我们的方法加深了对量子密钥分发的基本原理的理解，同时为量子密码网络开辟了新的有趣可能性