Photon-Pair Generation in Cold Atomic Ensemble for Long-Distance Quantum Communication

One of the common methods for overcoming limitation of long-distance quantum communication is using entangled photon pair sources between 1.5-$\mu $m band photon and near infrared photon. We investigate the three-photon electromagnetically induced absorption (TPEIA) and four-wave mixing (FWM) in the 5S$_{\mathrm{1/2}}$-5P$_{\mathrm{3/2}}$-4D$_{\mathrm{5/2}}$ transition of $^{\mathrm{87}}$Rb atoms. We will report the photon-pairs with 780-nm and 1.5-$\mu $m generated by spontaneous four-wave mixing in this transition of $^{\mathrm{87}}$Rb.