Daniele De Bernardis, LENS - European Laboratory for Non-Linear Spectroscopy, Florence, Italy

Leuchs-Russell-Auditorium, A.1.500, Staudtstr. 2

Location details

Abstract:

We theoretically study how the peculiar properties of the vacuum state of an ultra-strongly coupled system can affect basic light-matter interaction processes. In the ultrastrong coupling (USC) regime of cavity QED even a single photon acts non-perturbatively on matter and the ground-state of the whole combined system is predicted to be heavily populated by virtual photons. In this talk I review the recent and less recent debate about the USC regime, its experimental feasibility and its relation with the current discussion regarding the possibility of modifying material properties in the cavity vacuum. In particular, by using a simple ‘quantum optical’ toy model, I discuss how matter's thermalization is drastically altered in this extreme regime: the cavity USC inhibits relaxation of the open system (and thus thermalization), leaving only some narrow multi-photon resonances where fast thermalization can be restored. Beyond the full numerical solution, I introduce an analytical approach based on the generalised rotating-wave approximation of the Rabi model, valid in the so-called polaron frame in the USC regime.

[1] Relaxation breakdown and resonant tunneling in ultrastrong-coupling cavity QED, Daniele De Bernardis, Phys. Rev. A 108, 043717, (2023).
[2] Tutorial on nonperturbative cavity quantum electrodynamics: is the Jaynes–Cummings model still relevant?, Daniele De Bernardis, Alberto Mercurio, and Simone De Liberato, JOSA B 41, 8, (2024).
[3] Light-matter interactions in the vacuum of ultra-strongly coupled systems, Daniele De Bernardis, Gian Marcello Andolina, Iacopo Carusotto, arXiv:2312.16287, (2023).
[4] Can We Observe Nonperturbative Vacuum Shifts in Cavity QED?, Rocío Sáez-Blázquez, Daniele de Bernardis, Johannes Feist, and Peter Rabl, Phys. Rev. Lett. 131, 013602, (2023).