Title: Cavity control of quantum many-body systems: From topology to photon condensation

Speaker: Prof. Titas Chanda, IIT Indore

Abstract: The field of cavity control involves exploring the collective behavior of quantum materials along with strong light-matter couplings in cavity quantum electrodynamics (cavity QED) setups. One of the key aims of this area of research is to modify the properties of quantum materials using cavity embedding, e.g., superconductivity, transport properties, ferroelectricity etc. In this seminar, I will first discuss how a cavity embedding in an ultra-cold atomic setup, driven by an external laser source, generates a non-trivial topological phase in the 1D Bose-Hubbard system. Such a topological phase belongs to a new group of topological insulators, called the ‘symmetry-breaking topological insulators’, where spontaneous breakdown of certain symmetry generates topological protection associated with another symmetry. I will also briefly touch upon the onset of other interesting quantum phases, such as different supersolid phases. In the second part of the seminar, I will move on to talk about how to bypass the no-go theorems on spontaneous photon condensation in gauge-invariant cavity QED systems. Specifically, I will demonstrate that by considering a minimal setting beyond 1D, such as a two-leg ladder geometry where the orbital motion of spinless fermions is coupled through Peierls substitution to a non-uniform cavity mode, photons can indeed be condensed. Our analytical interpretation of this photon condensation will be scrutinized against large scale density-matrix renormalization group simulations.

Refs.: Quantum 5, 501 (2021), Phys. Rev. B 106, 075137 (2022), Phys. Rev. B 106, 155113 (2022), SciPost Physics 15, 113 (2023).