Quantum-enhanced optical systems operating within the 2- to 2.5-μm spectral region have the potential to revolutionize emerging applications in communications, sensing, and metrology. However, to date, sources of entangled photons have been realized mainly in the near-infrared 700- to 1550-nm spectral window. Here, using custom-designed lithium niobate crystals for spontaneous parametric down-conversion and tailored superconducting nanowire single-photon detectors, we demonstrate two-photon interference and polarization-entangled photon pairs at 2090 nm. These results open the 2- to 2.5-μm mid-infrared window for the development of optical quantum technologies such as quantum key distribution in next-generation mid-infrared fiber communication systems and future Earth-to-satellite communications.

在 2 至 2.5 μm 光谱范围内工作的量子增强光学系统有可能彻底改变通信、传感和计量领域的新兴应用。然而，迄今为止，纠缠光子源主要在近红外 700 至 1550 nm 光谱窗口中实现。在这里，我们使用定制设计的铌酸锂晶体进行自发参量下转换和定制的超导纳米线单光子探测器，在 2090 nm 处演示了双光子干涉和偏振纠缠光子对。这些结果为光量子技术的发展打开了2至2.5μm中红外窗口，例如下一代中红外光纤通信系统中的量子密钥分配和未来地对卫星通信。