Quantum communication schemes such as quantum key distribution (QKD) and superdense teleportation provide unique opportunities to communicate information securely. Increasingly, optical communication is being extended to free-space channels, but atmospheric turbulence in free-space channels requires optical receivers and measurement infrastructure to support many spatial modes. Here we present a multi-mode, Michelson-type time-delay interferometer using a field-widened design for the measurement of phase-encoded states in free-space communication schemes. The interferometer is constructed using glass beam paths to provide thermal stability, a field-widened angular tolerance, and a compact footprint. The performance of the interferometer is highlighted by measured visibilities of $99.02\pm 0.05\%$, and $98.38\pm 0.01\%$ for single- and multi-mode inputs, respectively. Additionally, high quality multi-mode interference is demonstrated for arbitrary spatial mode structures and for temperature changes of $\pm 1.0{}^{\circ }$C. The interferometer has a measured optical path-length drift of $130$nm$/{}^{\circ }$C near room temperature. With this setup, we demonstrate the measurement of a two-peaked, multi-mode, single-photon state used in time-phase QKD with a visibility of $97.37\pm 0.01\%$.

中文翻译：

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用于自由空间量子通信的多模时延干涉仪

量子通信方案，例如量子密钥分配（QKD）和超稠密的隐形传态，为安全地传递信息提供了独特的机会。光通信越来越多地扩展到自由空间信道，但是自由空间信道中的大气湍流需要光接收器和测量基础设施来支持许多空间模式。在这里，我们提出了一种多模，迈克尔逊型时延干涉仪，该仪采用了场扩展设计，用于测量自由空间通信方案中的相位编码状态。干涉仪是使用玻璃光束路径构造的，以提供热稳定性，场宽角公差和紧凑的占地面积。干涉仪的性能通过测量$99.02\pm 0.05％$和 $98.38\pm 0.01％$分别用于单模式和多模式输入。此外，还针对任意空间模式结构和温度变化证明了高质量的多模式干扰。$\pm 1.0{}^{\circ }$C.干涉仪测得的光程长度漂移为 $130$纳米$/{}^{\circ }$室温附近。通过此设置，我们演示了在时相QKD中使用的两峰，多模式，单光子状态的测量，可见度为$97.37\pm 0.01％$。