Dynamical Casimir effect in cavities with two modes resonantly coupled through a qubit

Abstract

We revisit the dynamical Casimir effect in high-quality multimode cavities, namely, generation of photons from vacuum due to fast external variation of system parameters. In one-dimensional case the spectrum of modes is equidistant, so for harmonic modulation an infinite number of modes become excited. But only one mode is usually excited in cavities with nonequidistant spectrum, apart from some exceptional configurations for which two or three modes are populated. Here is unveiled another scenario in which a small number of photons is generated from vacuum in two specific modes of a cavity with special spectrum profile. The scheme relies on strongly coupling the field to an initially unexcited qubit, whose frequency undergoes a weak harmonic perturbation. When the ratio between two modes' frequencies is accurately tuned in the vicinity of 3, these modes and the qubit can be driven to tripartite entangled states due to narrow three-photon resonances.