Strongly localized polaritons in an array of trapped two-level atoms interacting with a light field

TL;DR

This paper introduces a polaritonic crystal structure where coupled atom-field states can slow or stop light, demonstrating a phase transition to a superfluid state of polaritons with controllable group velocity.

Contribution

It proposes a novel polaritonic crystal system with a phase transition to a superfluid state, linking polariton properties to the atomic medium's polarization and photon number.

Findings

Observation of slow and stopped light phenomena in the polaritonic crystal.

Identification of a phase transition to a superfluid BCS-like state of polaritons.

Group velocity of polaritons depends on the system's order parameter.

Abstract

We propose a new type of spatially periodic structure, i.e. polaritonic crystal (PolC), to observe a "slow"/"stopped" light phenomenon due to coupled atom-field states (polaritons) in a lattice. Under the tightbinding approximation, such a system realizes an array of weakly coupled trapped two-component atomic ensembles interacting with optical field in a tunnel-coupled one dimensional cavity array. We have shown that the phase transition to the superfluid Bardeen-Cooper-Schrieffer state, a so-called (BCS)-type state of low branch polaritons, occurs under the strong coupling condition. Such a transition results in the appearance of a macroscopic polarization of the atomic medium at non-zero frequency. The principal result is that the group velocity of polaritons depends essentially on the order parameter of the system, i.e. on the average photon number in the cavity array.