Dicke transition in open many-body systems determined by fluctuation effects

SPICE Workshop on Quantum Spinoptics, June 13th - 15th 2023

Achim Rosch

In recent years, one important experimental achievement was the strong coupling of quantum matter and quantum light. Realizations reach from ultracold atomic gases in high-finesse optical resonators to electronic systems coupled to THz cavities. At sufficient strong coupling, these systems realize a Dicke transition where where the cavity mode becomes macroscopically occupied accompanied by the emergence of a self-organized phase of the matter fields.
Nominally, a mean-field treatment of the cavity mode becomes exact in the thermodynamic limit. We argue [1], however, that the stationary state of the system and thus the Dicke transition in the stationary state is determined by fluctuation effects beyond mean field. We validate our results by comparing to time-dependent matrix-product-state calculations.

[1] Alla V. Bezvershenko, Catalin-Mihai Halati, Ameneh Sheikhan, Corinna Kollath, and Achim Rosch Phys. Rev. Lett. 127, 173606 (2021)