High-dimensional quantum key distribution (QKD) offers secure communication, with secure key rates that surpass those achievable by QKD protocols utilizing two-dimensional encoding. However, existing high-dimensional QKD protocols require additional experimental resources, such as multiport interferometers and multiple detectors, thus raising the cost of practical high-dimensional systems and limiting their use. Here, we present and analyze a novel protocol for arbitrary-dimensional QKD, that requires only the hardware of a standard two-dimensional system. We provide security proofs against individual attacks and coherent attacks, setting an upper and lower bound on the secure key rates. Then, we test the new high-dimensional protocol in a standard two-dimensional QKD system over a 40 km fiber link. The new protocol yields a two-fold enhancement of the secure key rate compared to the standard two-dimensional coherent one-way protocol, without introducing any hardware modifications to the system. This work, therefore, holds great potential to enhance the performance of already deployed time-bin QKD systems through a software update alone. Furthermore, its applications extend across different encoding schemes of QKD qudits.

翻译：高维量子密钥分发（QKD）提供了安全通信，其安全密钥速率超过了采用二维编码的QKD协议所能达到的速率。然而，现有的高维QKD协议需要额外的实验资源，例如多端口干涉仪和多个探测器，从而提高了实用高维系统的成本并限制了其应用。在此，我们提出并分析了一种适用于任意维QKD的新协议，该协议仅需标准二维系统的硬件。我们提供了针对个体攻击和相干攻击的安全证明，设定了安全密钥速率的上限和下限。随后，我们在40公里光纤链路上的标准二维QKD系统中测试了这一新高维协议。与标准二维相干单向协议相比，新协议在不引入任何硬件修改的情况下，使安全密钥速率提升了两倍。因此，这项工作仅通过软件更新就具有增强已部署的时间箱QKD系统性能的巨大潜力。此外，其应用还扩展到QKD量子态的不同编码方案中。