Quantum vacuum properties of the intersubband cavity polariton field

TL;DR

This paper explores the quantum properties of intersubband cavity polaritons in microcavities, revealing ultra-strong coupling regimes, ground state squeezing, and potential for photon pair generation via vacuum manipulation.

Contribution

It introduces a quantum model of intersubband polaritons showing tunable ultra-strong coupling and vacuum properties, with implications for quantum optics and photon generation.

Findings

Ultra-strong light-matter coupling regime identified

Ground state exhibits two-mode squeezing

Vacuum tunability enables photon pair production

Abstract

We present a quantum description of a planar microcavity photon mode strongly coupled to a semiconductor intersubband transition in presence of a two-dimensional electron gas. We show that, in this kind of system, the vacuum Rabi frequency $\Omega\_R$ can be a significant fraction of the intersubband transition frequency $\omega\_{12}$. This regime of ultra-strong light-matter coupling is enhanced for long wavelength transitions, because for a given doping density, effective mass and number of quantum wells, the ratio $\Omega\_R/\omega\_{12}$ increases as the square root of the intersubband emission wavelength. We characterize the quantum properties of the ground state (a two-mode squeezed vacuum), which can be tuned {\it in-situ} by changing the value of $\Omega\_R$, e.g., through an electrostatic gate. We finally point out how the tunability of the polariton quantum vacuum can be exploited to generate correlated photon pairs out of the vacuum via quantum electrodynamics phenomena reminiscent of the dynamic Casimir effect.