Single-photon switching inside a polarizatcavityion-selective*

We propose a scheme for single-photon switching that employs the phenomenon of vacuum induced transparency (VIT) and an ensemble of a three-level atoms in a polarization-selective cavity. In this system, light of one polarization (H) couples to one of the atomic transitions with high single-atom cooperativity, while the orthogonal polarization (V) couples to the other atomic transition. When both a weak probe and the cavity mode are resonant with their respective transitions, the otherwise opaque system becomes transparent to the probe through VIT.
By setting the cavity mode and probe field far detuned, the regime of a Raman two-photon absorption (TPA) is reached, however because we use a vacuum cavity mode, this may be referred to as a vacuum induced Raman absorption (VIRA). The benefit of this regime is that the resonance condition for the VIT, allowing for full transmission, and the VIRA, resulting in a large absorption, can be very close in frequency. We exploit this by setting the probe photon on the VIRA resonance. The optical switch can then be opened by injecting a single photon into the cavity mode, shifting the VIRA resonance such that the probe field is instead at the VIT resonance, allowing for large transmission.