Efficient Biphoton Generation from Dense Chip-Scale Cesium Vapor Cell

Photonic quantum sources based on atomic ensembles are excellent candidates for hybrid photonic quantum networks due to their high brightness, low noise levels, and narrow spectral bandwidth. These networks require the generation of photonic quantum states from diverse systems, such as atomic ensembles and quantum dots. Here, we present a novel platform for a highly efficient biphoton source, utilizing a thin and dense atomic medium in a 1-mm-long chip-scale cesium (Cs) vapor cell.

Bright, strongly correlated biphotons are generated through spontaneous four-wave mixing in the dense cesium atomic ensemble, exploiting the 6S_1/2-6P_3/2-6D_5/2 cascade transitions of ¹³³Cs. In our system, the signal photon is emitted at 917 nm, while the idler photon is emitted at 852 nm. Both photons are detected using a superconducting nanowire single-photon detector (SNSPD), despite being optimized for 780 nm, achieve quantum efficiencies of approximately 50% for the signal photon and 70% for the idler photon. Our biphoton source achieves a detected biphoton count rate of 1000 kilo-counts per second, a heralding efficiency of 24%, and a maximum normalized second-order cross-correlation function value of 280 between the signal and idler photons.

We believe this highly efficient photon source offers a promising approach for the development of scalable hybrid quantum networks, paving the way for advancements in quantum communication and quantum information processing.