Brantut, Jean-Philippe

Date:   Thursday, February 25, 2021
Time:   10:00
Place:   scheduled Zoom meeting
Host:    Klaus Ensslin

Exploring strongly correlated quantum matter using cavity quantum electrodynamics

Jean-Philippe Brantut
EPF Lausanne

Cavity quantum electrodynamics (QED) is one of the most powerful framework to observe quantum systems with high sensitivity. While it has been thoroughly studied for simple quantum systems such as two-level systems or harmonic oscillators, it has only recently become available for complex, correlated quantum many-body systems [1,2]. We have developed a setup combining cavity QED with quantum degenerate Fermi gas with tunable interactions, realizing the simultaneous control of both atom-atom and light-matter interactions up to the strong coupling regime [3]. In this talk, I will present the observation of strong coupling between photons in a high-finesse cavity and Fermions in a strongly correlated superfluid. I will then show that in addition to single atom coupling, photons also couple strongly to Fermion pairs via molecular transitions, yielding a new type composite excitations, pair polaritons. We show that the pair-polariton spectrum faithfully maps the strong correlations in the ground state of the Fermi gas, bridging up a two-orders of magnitude gap in energy between the Fermi energy of the gas and the scale of optical excitations. By coupling the gas to the atoms dispersively, we demonstrate weakly destructive, repeated measurements of both atomic populations and pair correlations over a single cloud. The convergence of quantum optics tools with correlated Fermions physics opens many perspectives, from light-induced phases of matter to quantum limited measurements of many-body dynamics.

[1] J. Klinder, et al Phys. Rev. Lett. 115, 230403 (2015)
[2] R. Landig, et al Nature 532, 476 (2016)
[3] K. Roux, et al Nature Communications 11:2974 (2020)