High-efficiency submegahertz bandwidth photon pair generators will enable the field of quantum technology to transition from laboratory demonstrations to transformational applications involving information transfer from photons to atoms. While spontaneous parametric processes are able to achieve high-efficiency photon pair generation, the spectral bandwidth tends to be relatively large, as defined by phase-matching constraints. To solve this fundamental limitation, we use an ultrahigh quality factor ($Q$) fused silica microsphere resonant cavity to form a photon pair generator. We present the full theory for the spontaneous four-wave mixing (SFWM) process in these devices, fully taking into account all relevant source characteristics in our experiments. The exceptionally narrow (down to kilohertz-scale) linewidths of these devices result in a reduction in the bandwidth of the photon pair generation, allowing submegahertz spectral bandwidth to be achieved. Specifically, using a pump source centered around 1550 nm, photon pairs with the signal and idler modes at wavelengths close to 1540 and 1560 nm, respectively, are demonstrated. We herald a single idler-mode photon by detecting the corresponding signal photon, filtered via transmission through a wavelength division multiplexing channel of choice. We demonstrate the extraction of the spectral profile of a single peak in the single-photon frequency comb from a measurement of the signal–idler time of emission distribution. These improvements in device design and experimental methods enabled the narrowest spectral width ($\mathrm{\Delta }\nu =366\mathrm{kHz}$) to date in a heralded single-photon source based on SFWM.

中文翻译：

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基于熔融石英微球的亚兆赫谱宽光子对源

高效的亚兆赫带宽光子对发生器将使量子技术领域从实验室演示过渡到涉及从光子到原子的信息传输的转换应用。虽然自发参数过程能够实现高效的光子对生成，但光谱带宽往往相对较大，如相位匹配约束所定义的那样。为了解决这个基本限制，我们使用了超高品质因数（$问$) 熔融石英微球谐振腔形成光子对发生器。我们展示了这些设备中自发四波混频 (SFWM) 过程的完整理论，充分考虑了我们实验中的所有相关源特性。这些设备的异常窄（低至千赫级）线宽导致光子对生成的带宽减少，从而可以实现亚兆赫的光谱带宽。具体来说，使用以 1550 nm 为中心的泵浦源，分别演示了波长接近 1540 和 1560 nm 的具有信号和闲散模式的光子对。我们通过检测相应的信号光子来预示单个空闲模式光子，该信号光子通过选择的波分复用通道传输进行过滤。我们展示了从发射分布的信号空闲时间的测量中提取单光子频率梳中单个峰的光谱轮廓。这些设备设计和实验方法的改进使光谱宽度最窄（$\mathrm{\Delta }\nu =366\mathrm{千赫}$) 迄今为止在基于 SFWM 的预示单光子源中。