Interaction-Free All-Optical Switching in Coupled Cavities

All-optical switching is important for applications in optical communications and quantum information networks. Generally, all-optical switching relies on the large optical nonlinearities induced in an optical medium by coupling of the signal and control light. However, the switching efficiency is limited by the photon loss due to absorption or scattering during the coupling of the signal light and control light. In order to operate an all-optical switch with low photon absorption or scattering, it is necessary to generate large optical nonlinearities in an interaction-free way, i.e., the signal light and control light are not directly coupled in the optical medium. In this paper, we propose a scheme for the interaction-free all-optical switching in the coupled cavities based on the quantum interference effect. Two cavities are coupled by the photon tunneling effect. N Λ-type three level atoms are trapped in the second cavity and they are resonantly coupled to the cavity mode. When a control light is coupled to the atoms with a certain detuning, the input signal light is reflected by the first cavity such that there is no direct coupling between the control light and signal light in the atom-cavity system. Therefore, our scheme for all-optical switching is in an interaction-free manner. We only require the cavity condition √g²N+J² >>κ,γ where g√N is the collective coupling coefficient between the cavity mode and atoms, J is the tunneling coefficient between two cavities, κ is the decay rate of the cavity mode, and γ denotes the decay rate of excited state of the atoms. When J >>κ,γ, even though the cavity strong coupling condition g√N >>κ,γ is not satisfied, the required condition in our scheme √g²N+J² >>κ,γ can still be satisfied well, which can relax strong coupling conditions in the experimental implementation of all-optical switching. The scheme proposed in this paper offers a promising approach to achieve the interaction-free all-optical switching.