Direct generation of polarization-entangled photons from warm atomic ensemble

Abstract

We experimentally realized a bright and robust polarization-entangled photon-pair source from Doppler-broadened atomic ensembles by exploiting the strong signal-idler polarization correlation. The photon pair is emitted from the cascade-type 5S1/2–5P3/2–5D5/2 transition of 87Rb. Without using an interferometric configuration, we robustly produce all four Bell states by applying the intrinsic polarization correlation achieved in a cascade-type atomic system. The coincidence count rate of the polarization-entangled photon pairs is measured as 10.0(1) kHz under a weak pump power of 20 μW. Our scheme enables the generation of a high rate of polarization-entangled photon pairs with a high fidelity of 0.933(2). We believe that our approach to realize bright and stable polarization-entangled photon-pair sources can contribute to the construction of practical scalable quantum networks based on atom–photon interactions.