An efficient, tunable, and robust source of narrow-band photon pairs at the 87Rb D1 line

We present an efficient and robust source of photons at the Rb-87 D1-line (795 nm) with a narrow bandwidth of delta = 226(1) MHz. The source is based on non-degenerate, cavity-enhanced spontaneous parametric down-conversion in a monolithic optical parametric oscillator far below threshold. The setup allows for efficient coupling to single mode fibers. A heralding efficiency of eta(heralded) =45(5) % is achieved, and the uncorrected number of detected photon pairs is 3.8 x 10(3)/(s mW). For pair generation rates up to 5x10(5)/s, the source emits heralded single photons with a normalized, heralded, second-order correlation function g(c)((2)) <0.01. The source is intrinsically stable due to the monolithic configuration. Frequency drifts are on the order of delta/20 per hour without active feedback on the emission frequency. We achieved fine-tuning of the source frequency within a range of >2 GHz by applying mechanical strain. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement