Generation of two-color correlated photon pairs at telecom wavelength from a warm atomic vapor cell

Quantum light sources in the telecom band are key components for long-distance quantum communication technology. We report a high-performance telecom-wavelength bi-photon source from a hot 87Rb atomic vapor cell. The time-correlated photon pairs are generated from the cascade-type 5S1/2–5P3/2–4D5/2 transition of 87Rb via the spontaneous four-wave mixing process. Under the condition of a high optical depth of 112(3) including the two-photon absorption with a spectral width of 260 MHz, we measure the maximum normalized cross-correlation value of 44(3) with a weak pump power of 2 μW and the full width at half maximum of cross-correlation function of 0.56(4) ns. We obtained the violation of the Cauchy-Schwarz inequality by a factor of more than 650. The high generation rate of the photon pairs is estimated as 108-order cps/mW. Furthermore, according to theoretical analysis from the 4-level atomic configuration, we examine the bi-photon spectral waveform (based on a stimulated emission tomography) and temporal waveform (based on cross-correlation function) of our photon pair source and confirm that the biphoton waveforms of photon pairs generated from the cascade-type transition are significantly affected by wavelengths difference between the lower and upper transition of the three-level atomic cascade system. We believe that our telecom-wavelength bi-photon source from an atomic vapor cell has useful in the application of long-distance quantum networks and in the context of realizing practical quantum repeater based on atom–photon interactions.