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

Abstract

We present an efficient and robust source of photons at the ${}^{87}$Rb D1-line (795 nm) with a narrow bandwidth of $\hat{I}´=226(1)$ 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 $\hat{I}{\cdot }_{\mathrm{heralded}}=45(5)$ % is achieved, and the uncorrected number of detected photon pairs is $3.8\times 10^3/(\text{s mW})$. For pair generation rates up to $5\times 10^5/$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 $\hat{I}´/20$ 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.

6 pages, 4 figures