Flying atom back-reaction and mechanically generated photons from vacuum

TL;DR

This paper explores the complex dynamics of a flying two-level atom in a cavity under ultrastrong coupling, revealing regimes where the atom is reflected or generates real photons from the vacuum, with implications for quantum control.

Contribution

It provides a full quantum model including atomic motion, uncovering new dynamical regimes and mechanisms like quantum regenerative braking in atom-cavity interactions.

Findings

Atom can be reflected by the dressed vacuum.

Part of the atom's kinetic energy can convert into real photons.

Different dynamical regimes depend on energy ratios and transit time.

Abstract

We investigate the dynamics of a two-level atom flying through a photonic cavity when the light-matter interaction is in the ultrastrong coupling regime. We adopt a closed full quantum description that takes into account the quantization of the atom center-of-mass motion in addition to its internal degree of freedom and to the quantized photonic cavity field. We find that multiple qualitatively different dynamical regimes are achievable according to two key figures of merit: the ratio between the kinetic energy and the bare excitation energies, and the product of these bare energies with the time the atom takes to fly through the cavity. According to the values of those figures of merit, the atom can be reflected by the \emph{dressed} vacuum, or can convert part of its kinetic energy into real excitations which might be emitted out of the cavity. In the first case, the atom experiences a \emph{quantum regenerative braking} mechanism, based on temporary storage of energy into virtual excitations.