Near-field dynamical Casimir effect

We propose the dynamical Casimir effect in a time-modulated near-field system at finite temperatures. The system consists of two bodies made of polaritonic materials, that are brought in close proximity to each other, and the modulation frequency is approximately twice the relevant resonance frequencies of the system. We develop a rigorous fluctuational electrodynamics formalism to explore the produced Casimir flux, associated with the degenerate as well as non-degenerate two-polariton emission processes. We have identified flux contributions from both quantum and thermal fluctuations at finite temperatures, with a dominant quantum contribution even at room temperature under the presence of a strong near-field effect. We have found that the Casimir flux can be generated with a smaller modulation frequency through higher-order dynamical Casimir effect. We have conducted a nonclassicality test for the total radiative flux at finite temperatures, and shown that nonclassical states of emitted photons can be obtained for a high temperature up to $\sim 250\,$K. Our findings open an avenue for the exploration of dynamical Casimir effect beyond cryogenic temperatures, and may be useful for creating tunable nanoscale nonclassical thermal states.