Highly efficinet biphoton generation from thin atomic ensemble

For hybrid photonic quantum networks between the photonic quantum states generated from different systems, such as atoms and quantum dots, photonic quantum sources based on an atomic ensemble are excellent potential resources with brightness, low-noise, and narrowband. We present a highly bright biphoton generated from the 1-mm-long thin atomic medium of the chip-scale Cs atomic vapor cell. The strongly correlated biphotons are obtained via spontaneous four-wave mixing from a warm atomic ensemble of the 6S1/2–6P3/2–6D5/2 transition of 133Cs. The performance of our biphoton source from the thin atomic ensemble has the detected biphoton count rate of 97.4(5) kilo-counts per second, the heralding efficiency of 12.5(1)%, and the normalized cross-correlation value of 115(7) between the signal and idler photons, regardless of the low detection efficiency of a silicon avalanche photodetector of less than 30% at 917 nm. We obtained the maximal violation of the Cauchy-Schwarz inequality by a factor of >106 at the pump power of 1 mW. We believe that our scheme for highly efficient photon source is making it useful for scalable quantum networks.