# Collective optomechanical effects in cavity quantum electrodynamics

## TL;DR

This paper explores how collective coupling in cavity quantum electrodynamics can induce a phase transition in freely rotating optical dipoles, affecting their alignment and polariton resonance, bridging cavity QED and quantum optomechanics.

## Contribution

It introduces a novel phase transition mechanism driven by collective light-matter interactions in cavity QED systems, linking optical dipole alignment with optomechanical effects.

## Key findings

- Identifies a second order phase transition between isotropic and aligned dipole states.
- Demonstrates an intensity-dependent shift in polariton mode resonance.
- Establishes a formal analogy between rotating dipoles and polymer models.

## Abstract

We investigate a cavity quantum electrodynamic effect, where the alignment of two-dimensional freely rotating optical dipoles is driven by their collective coupling to the cavity field. By exploiting the formal equivalence of a set of rotating dipoles with a polymer we calculate the partition function of the coupled light-matter system and demonstrate it exhibits a second order phase transition between a bunched state of isotropic orientations and a stretched one with all the dipoles aligned. Such a transition manifests itself as an intensity-dependent shift of the polariton mode resonance. Our work, lying at the crossroad between cavity quantum electrodynamics and quantum optomechanics, is a step forward in the on-going quest to understand how strong coupling can be exploited to influence matter internal degrees of freedom.