# Squeezed light induced symmetry breaking superradiant phase transition

## TL;DR

This paper theoretically demonstrates that squeezed light can induce a quantum phase transition in cavity QED systems, enabling control over superradiant phases without ultrastrong coupling, and reveals a tricritical point where phase transition orders meet.

## Contribution

It introduces a novel mechanism for quantum phase transition driven by squeezed light, bypassing the need for ultrastrong coupling, and identifies a tricritical point in the phase diagram.

## Key findings

- Squeezed light induces symmetry-breaking superradiant phase transition.
- Existence of a tricritical point where first- and second-order transitions meet.
- Optical switching between phases controlled by squeezed light intensity.

## Abstract

We theoretically investigate the quantum phase transition in the collective systems of qubits in a high-quality cavity, which is driven by a squeezed light. We show that the squeezed light induced symmetry breaking can result in quantum phase transition without the ultrastrong coupling requirement. Using the standard mean field theory, we derive the condition of the quantum phase transition. Surprisingly, we show that there exists a tricritical point where the first- and second-order phase transitions meet. With specific atom-cavity coupling strengths, both the first- and second-order phase transition can be controlled by the squeezed light, leading to an optical switching from the normal phase to the superradiant phase by just increasing the squeezed light intensity. The signature of these phase transitions can be observed by detecting the phase space Wigner function distribution with different profiles controlled by the squeezed light intensity. Such superradiant phase transition can be implemented in various quantum systems, including atoms, quantum dots and ions in optical cavities as well as the circuit quantum electrodynamics system.