Centre for Quantum Technologies, National University of Singapore, 3 Science Drive 2, Singapore 117543, Singapore.
Phys Rev Lett. 2013 Sep 20;111(12):123602. doi: 10.1103/PhysRevLett.111.123602. Epub 2013 Sep 17.
We observe narrow band pairs of time-correlated photons of wavelengths 776 and 795 nm from nondegenerate four-wave mixing in a laser-cooled atomic ensemble of ^{87}Rb using a cascade decay scheme. Coupling the photon pairs into single mode fibers, we observe an instantaneous rate of 7700 pairs per second with silicon avalanche photodetectors, and an optical bandwidth below 30 MHz. Detection events exhibit a strong correlation in time [g((2))(τ = 0) ≈ 5800] and a high coupling efficiency indicated by a pair-to-single ratio of 23%. The violation of the Cauchy-Schwarz inequality by a factor of 8.4 × 10(6) indicates a strong nonclassical correlation between the generated fields, while a Hanbury Brown-Twiss experiment in the individual photons reveals their thermal nature. The comparison between the measured frequency bandwidth and 1/e decay time of g((2)) indicates a transform-limited spectrum of the photon pairs. The narrow bandwidth and brightness of our source makes it ideal for interacting with atomic ensembles in quantum communication protocols.
我们使用级联衰变方案，在激光冷却的 ^{87}Rb 原子系综中观察到非简并四波混频产生的波长为 776nm 和 795nm 的窄带宽时间相关光子对。将光子对耦合到单模光纤中，我们使用硅雪崩光电探测器观察到每秒 7700 对的瞬时速率，并且光学带宽低于 30MHz。检测事件在时间上表现出很强的相关性[g((2))(τ=0)≈5800]，并且通过对 23%的单光子到双光子的转换效率表明具有很高的耦合效率。由于 Cauchy-Schwarz 不等式被违反了 8.4×10(6)倍，这表明生成的场之间具有很强的非经典相关性，而在单个光子中的 Hanbury Brown-Twiss 实验则揭示了它们的热性质。对测量的频率带宽和 g((2))的 1/e 衰减时间的比较表明，光子对具有变换限制的光谱。我们的光源具有窄带宽和高亮度，使其成为量子通信协议中与原子系综相互作用的理想光源。
