Ultrabright, narrow-band photon-pair source for atomic quantum memories

Abstract

We demonstrate an ultrabright, narrow-band and frequency-tunable photon-pair source based on cavity-enhanced spontaneous parametric down conversion (SPDC) which is compatible with atomic transition of rubidium D2-line (780 nm) or cesium D2-line (852 nm). With the pump beam alternating between a high and a low power phase, the output is switching between the optical parametric oscillator (OPO) and photon-pair generation mode. We utilize the OPO output light to lock the cavity length to maintain the double resonances of signal and idler, as well as to lock the signal frequency to cesium atomic transition. With a type-II phase matching and a double-passed pump scheme such that the cluster frequency spacing is larger than the SPDC bandwidth, the photon-pair output is in a nearly single-mode operation as confirmed by a scanning Fabry–Perot interferometer with its output detected by a photomultiplier. The achieved generation and detection rates are and 6142 s−1 mW−1, respectively. The correlation time of the photon pair is 21.6(2.2) ns, corresponding to a bandwidth of 2π × 6.6(6) MHz. The spectral brightness is s−1 mW−1 MHz−1. This is a relatively high value under a single-mode operation with the cavity-SPDC scheme. The generated single photons can be readily used in experiments related to atomic quantum memories.