# Polariton Laser in the Bardeen-Cooper-Schrieffer Regime

## TL;DR

This paper demonstrates the existence of a polaritonic Bardeen-Cooper-Schrieffer (BCS) state in microcavity exciton polariton systems, revealing a fermionic gain mechanism through experimental and theoretical analysis.

## Contribution

It provides the first direct experimental evidence and theoretical modeling of a polariton BCS state at intermediate densities.

## Key findings

- Revealed fermionic gain mechanism in polariton lasing
- Identified polariton BCS state as an intermediate density phase
- Linked experimental observations with many-particle theory

## Abstract

Microcavity exciton polariton systems can have a wide range of macroscopic quantum effects that may be turned into better photonic technologies. Polariton Bose-Einstein condensation and photon lasing have been widely accepted in the limits of low and high carrier densities, but identification of the expected Bardeen-Cooper-Schrieffer (BCS) state at intermediate densities remains elusive, as the optical-gain mechanism cannot be directly inferred from existing experiments. Here, using a microcavity with strong polarization selectivity, we gain direct experimental access to the reservoir absorption in the presence of polariton condensation and lasing, which reveals a fermionic gain mechanism underlying the polariton laser. A microscopic many-particle theory shows that this polariton lasing state is consistent with an open-dissipative-pumped system analog of a polaritonic BCS state.