Cavity-enhanced Spontaneous parametric down-conversion (SPDC) is capable of efficient generation of single photons with suitable spectral properties for interfacing with the atoms. However, beside the remarkable progress of this technique, multi-mode longitudinal emission remains as major drawback. Here we demonstrate a bright source of single photons that overcomes this limitation by a novel mode-selection technique based on the introduction of an additional birefringent element to the cavity. This enables us to tune the double resonance condition independent of the phase matching, and thus to achieve single-mode operation without mode filters. Our source emits single-frequency-mode photons at 852 nm, which is compatible to the Cs D2 line, with a bandwidth of 10.9 MHz and a photon-pair generation rate exceeding 47 KHz at 10 mW of pump power, while maintaining a low $g^{\left(2\right)}(0) =$ 0.13. The efficiency of our source is further underlined by measuring a four-photon generation rate of 37 Hz at 20 mW of pump power. This brightness opens up a variety of new applications reaching from hybrid light-matter interactions to optical quantum information tasks based on long temporal coherence.
High-performance source of spectrally pure, polarization entangled photon pairs based on hybrid integrated-bulk optics
基于体光学的纠缠光子对光源正接近最佳设计和实现，具有高的态密度、光谱纯度和预示效率，但通常亮度较低。集成纠缠源，虽然提供更高的亮度和低功耗的操作，往往牺牲输出状态质量和耦合效率的性能。在这里，我们提出了一个偏振纠缠对源的基础上的波导和体光学的混合方法，同时解决每个度量。我们表现出96%的保真度的单重态，82%的Hong-Ou-Mandel干涉的可见度，43%的平均Klyshko效率，和高亮度的$2.9\times10^6$对/（模式$\cdot$ s $\cdot$ mW），而只需要微瓦的泵浦功率。
A wavelength-tunable fiber-coupled source of narrowband entangled photons
我们展示了一个波长可调的，光纤耦合的偏振纠缠光子源，具有极高的光谱亮度和纠缠质量。使用25 mm PPKTP晶体内的偏振Sagnac干涉仪，我们检测到的光谱亮度为273000对/（s mW nm），一个因素的28比以前可比的来源，而状态断层扫描显示的双光子状态有一个纠结的T=0.987。这种改进是通过使用长晶体、仔细选择聚焦参数和单模光纤耦合实现的。我们证明，由于特定的几何形状的设置，信号和空闲波长可以在很宽的范围内调谐而不会损失纠缠。
Heralding efficiency and brightness optimization of a micro-ring resonator via tunable coupling
Quantum Engineering Technology Labs, H. H. Wills Physics Laboratory and School of Electrical, Electronic and Mechanical Engineering, University of Bristol（布里斯托大学电气、电子和机械工程学院、H.H.威尔斯物理实验室量子工程技术实验室）；School of Mathematical and Physical Sciences, University of Sheffield（谢菲尔德大学数学与物理科学学院）
