Positronium density measurements using polaritonic effects

TL;DR

This paper proposes a novel polaritonic method to measure dense positronium (Ps) densities in real-time using vacuum Rabi splitting in microcavities, facilitating Ps Bose-Einstein Condensate research.

Contribution

It introduces a new spectroscopic approach leveraging polaritonic effects to determine Ps density rapidly and explores the potential for ultrastrong coupling regimes.

Findings

Vacuum Rabi splitting is proportional to the square root of Ps density.

Strong coupling regime enables ultra-fast density measurements.

Potential to reach ultrastrong light-matter coupling with positronium-polaritons.

Abstract

Recent experimental advances in Positronium (Ps) physics have made it possible to produce dense Ps ensembles in which Ps-Ps interactions may occur, leading to the production of Ps$_2$ molecules and paving the way to the realization of a Ps Bose-Einstein Condensate (BEC). In order to achieve this latter goal it would be advantageous to develop new methods to measure Ps densities in real-time. Here we describe a possible approach to do this using polaritonic methods: using realistic experimental parameters we demonstrate that a dense Ps gas can be strongly coupled to the photonic field of a distributed Bragg reflector microcavity. In this strongly coupled regime, the optical spectrum of the system is composed of two hybrid positronium-polariton resonances separated by the vacuum Rabi splitting, which is proportional to the square root of the Ps density. Given that polaritons can be created on a sub-cycle timescale, a spectroscopic measurement of the vacuum Rabi splitting could be used as an ultra-fast Ps density measurement in regimes relevant to Ps BEC formation. Moreover, we show how positronium-polaritons could potentially enter the ultrastrong light-matter coupling regime, introducing a radically novel platform to explore its non-perturbative phenomenology.