Collective terahertz fluctuation modes in a polariton laser

TL;DR

This paper demonstrates that collective fluctuation modes with different orbital angular momentum in a polariton BCS state can be excited using terahertz radiation, revealing new physical phenomena such as terahertz gain.

Contribution

It introduces a method to excite and observe collective fluctuation modes with non-zero angular momentum in a polariton BCS state using terahertz radiation.

Findings

Identification of collective modes with orbital angular momentum different from the order parameter.

Observation of terahertz gain as a physical manifestation of these modes.

Extension of fluctuation mode analysis to open quantum systems with symmetry breaking.

Abstract

A polariton Bardeen-Cooper-Schrieffer (BCS) state in a semiconductor microcavity is an example of symmetry-broken states in open systems. Fluctuations of the order parameter are an important tool to characterize such a state. With the condensate formed by composite particles, the set of zero-momentum fluctuations spans an infinite-dimensional electron-hole mode subspace. We show that collective fluctuation modes with orbital angular momentum different from that of the order parameter can be obtained with terahertz radiation, and that a physical manifestation of such modes, which are not Higgs modes, can be terahertz gain.