Properties of generated photon-pairs via ladder-type configurations with different excited levels in cesium vapor cell

Single photon sources are foundation blocks in quantum information technology. There are so many candidates to create single photon sources such as atoms, nonlinear crystal, quantum dot, NV center etc. Among them, atoms can be used to create reproducible photonic system because the photons emitted by atoms have always same optical properties. In the quantum communication field, single photon sources having a narrow linewidth is needed to exploit many frequency channels and strong interaction between light and atom for atom-based quantum memory. One of the typical way to obtain the source is to use four-wave-mixing from a hot atomic ensemble.

However, because it is difficult to change the optical properties of atom, we have to select energy levels of atom carefully and design the system to take advantage of geometric structure. In this work, experiments were conducted using two ladder-type energy level structures, 133Cs 6S_1/2-6P_3/2-8S_1/2 and 6S_1/2-6P_3/2-6D_5/2 transition, with warm cesium vapor cell. We measured single photon counts and time correlation between signal and idler photons varing pump and coupling laser power.

We can calculate the time correlation of photon-pair sources in 6S_1/2-6P_3/2-8S_1/2 and 6S_1/2-6P_3/2-6D_5/2 transitions. In the 6S_1/2-6P_3/2-8S_1/2 case, we observed the quantum beats of the temporal biphoton waveform of the photon pair due to the multiple channels of the SFWM process relating to the hyperfine states of the intermediate 6P_3/2 state in the 6S_1/2-6P_3/2-8S_1/2 transition.