Introduction to non-perturbative cavity quantum electrodynamics
Simone De Liberato
University of Southampton
When: Wednesday, February 13, 2019 – 2:00 pm
Where: Seminarraum N110, Altbau Physik, Geschwister-Scholl-Platz 1
The interaction of light with matter in usually described in terms of photons absorbed, emitted, or scattered by massive objects. The conceptual simplicity of such a framework rests on the small strength of the electromagnetic force, which allows us to describe electromagnetic interactions in terms of first order (absorption, emission) and second order (scattering) processes.
In carefully engineered nanostructures it is nevertheless possible, by confining photons in sub-wavelength volumes and increasing the density of dipoles, to engineer very large interactions between light and matter. A novel interaction regime can then be achieved, usually referred to as ultrastrong coupling, in which electromagnetism becomes non-perturbative. This leads to a completely novel phenomenology in which light and matter loose their individual identity .
In this talk I will introduce the basic theory of non-perturbative cavity quantum electrodynamics, present some of its most important experimental realisations, and discuss a few aspects of its rich phenomenology.
On the fundamental side, I will discuss how the non-perturbative vacuum contains a population of bound virtual photons, which can be detected when the system is perturbed . On the more applied side, I will show how for large enough couplings the Purcell effect dramatically breaks down and light and matter effectively decouple, posing an ultimate quantum limit to the working frequency of optoelectronic devices [3,4].
Finally, I will demonstrate how non-perturbative light-matter interaction can be exploited to engineer novel quantum materials with unique electronic and optical properties .
 Kockum et al., Nature Reviews Physics 1, 19 (2019).
 De Liberato, Nature Communications 8, 1465 (2017).
 De Liberato, Phys. Rev. Lett. 112, 016401 (2014).
 Muñoz et al., Nature Communications 9, 1924 (2018).
 Cortese et al., arXiv:1809.08876.