We present a device designed for two-step downconversion of single-photon-level signals at 650 nm to the 1.5-μm band with low excess noise and low required pump power as a quantum interface between matter-qubit-based nodes and low-loss photonic channels for quantum communication networks. The required pump power for this interface is around 60% of that for a comparable conventional single-pass device, which reduces the demand on the pump laser and yields a corresponding reduction in dark counts due to inelastic pump scattering. The single-photon-level signal at 649.7 nm is downconverted to the telecom band using a fiber-coupled reverse proton exchange periodically poled lithium niobate waveguide and a 2.19-μm pump laser. By testing the device in the linear regime with a classical input, we achieved 99% depletion efficiency for each stage, corresponding to an internal quantum efficiency of 63% at the optimum pump power for the complete cascaded process.

中文翻译：

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级联下变频接口，可将650 nm的单光子级信号转换为电信频段

我们提出了一种器件，该器件旨在将650 nm处的单光子级信号进行两步降频转换为1.5μm波段，具有较低的超额噪声和所需的低泵浦功率，可作为基于物质量子位的节点与低损耗之间的量子接口量子通信网络的光子通道。该接口所需的泵浦功率约为可比的传统单程设备的60％，这降低了对泵浦激光器的需求，并由于无弹性的泵浦散射而相应减少了暗计数。使用光纤耦合的反向质子交换周期性极化的铌酸锂波导和2.19μm泵浦激光器将649.7 nm的单光子级信号下变频到电信频段。通过使用经典输入在线性状态下测试该设备，我们在每个阶段都实现了99％的耗尽效率，