We demonstrate an on-demand source of microwave single photons with 71–99% intrinsic quantum efficiency. The source is narrowband (300 kHz) and tuneable over a 600 MHz range around 5.2 GHz. Such a device is an important element in numerous quantum technologies and applications. The device consists of a superconducting transmon qubit coupled to the open end of a transmission line. A π-pulse excites the qubit, which subsequently rapidly emits a single photon into the transmission line. A cancellation pulse then suppresses the reflected π-pulse by 33.5 dB, resulting in 0.005 photons leaking into the photon emission channel. We verify strong antibunching of the emitted photon field and determine its Wigner function. Non-radiative decay and 1/f flux noise both affect the quantum efficiency. We also study the device stability over time and identify uncorrelated discrete jumps of the pure dephasing rate at different qubit frequencies on a time scale of hours, which we attribute to independent two-level system defects in the device dielectrics, dispersively coupled to the qubit. Our single-photon source with only one input port is more compact and scalable compared to standard implementations.

我们展示了具有 71-99% 本征量子效率的按需微波单光子源。源是窄带 (300 kHz)，可在 5.2 GHz 附近的 600 MHz 范围内调谐。这种设备是众多量子技术和应用中的重要元素。该设备由耦合到传输线开放端的超导传输量子位组成。一个π脉冲会激发量子位，随后量子位会迅速将单个光子发射到传输线中。然后抵消脉冲将反射的π脉冲抑制33.5 dB，导致 0.005 个光子泄漏到光子发射通道中。我们验证了发射光子场的强反聚集并确定其 Wigner 函数。非辐射衰减和 1/ f通量噪声都会影响量子效率。我们还研究了器件随时间的稳定性，并在数小时的时间尺度上确定了不同量子位频率下纯移相率的不相关离散跳跃，我们将其归因于器件电介质中独立的两级系统缺陷，分散耦合到量子位。与标准实现相比，我们只有一个输入端口的单光子源更加紧凑和可扩展。