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

We present an efficient and robust source of photons at the 87Rb D1-line (795 nm) with a narrow bandwidth of δ = 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 ηheralded = 45(5) % is achieved, and the uncorrected number of detected photon pairs is 3.8 × 103/(s mW). For pair generation rates up to 5 × 105/s, the source emits heralded single photons with a normalized, heralded, second-order correlation function