Quantum theory seminar by Simon Balthasar Jäger, Bonn University

Simulating Cavity-Mediated Interactions and Dissipation

Coupling atoms to optical cavities provides a powerful platform for exploring collective phenomena that arise from strong light–matter interactions. In these systems, cavity photons mediate long-range interactions between atoms, enabling the study of many-body effects such as spin squeezing, subradiance, and superradiance. Beyond their fundamental interest, these phenomena also offer promising applications in quantum technologies. In this talk, I will highlight one such application: the superradiant laser. This device operates in a regime where the atomic coherence time exceeds the cavity photon lifetime by several orders of magnitude. As a result, the emitted light is highly robust against cavity-length fluctuations, making superradiant lasers attractive candidates for next-generation optical atomic clocks. Using the superradiant laser as a motivating example, I will discuss more generally how optical cavities can be used to engineer tailored interactions and dissipative processes in many-body quantum systems. I will present a theoretical framework that systematically integrates out the cavity degrees of freedom, yielding effective atom-only master equations that enable more efficient simulations of the dynamics. Building on these methods, which go beyond conventional mean-field descriptions, I will show how fluctuations can drive rich nonequilibrium phenomena, including supersonic spreading of correlations and fluctuation-induced bistability.