Spin and density self-ordering in dynamic polarization gradients fields

TL;DR

This paper explores the quantum phase diagram of a two-component Bose-Einstein condensate in an optical cavity, revealing multiple spin and density ordered phases controllable via laser parameters, with real-time experimental signatures.

Contribution

It demonstrates how a coupled atom-cavity system can realize complex spin and density orderings, mapping onto the $t$-$J$-$V$-$W$ model, and provides methods for real-time phase detection.

Findings

Identification of four distinct density- and spin-ordered phases.

Control of phases via pump strength and detuning.

Real-time signatures of phase transitions in emitted fields.

Abstract

We study the zero-temperature quantum phase diagram for a two-component Bose-Einstein condensate in an optical cavity. The two atomic spin states are Raman coupled by two transverse orthogonally-polarized, blue detuned plane-wave lasers inducing a repulsive cavity potential. For weak pump the lasers favor a state with homogeneous density and predefined uniform spin direction. When one pump laser is polarized parallel to the cavity mode polarization, the photons coherently scattered into the resonator induce a polarization gradient along the cavity axis, which mediates long-range density-density, spin-density, and spin-spin interactions. We show that the coupled atom-cavity system implements central aspects of the $t$-$J$-$V$-$W$ model with a rich phase diagram. At the mean-field limit we identify at least four qualitatively distinct density- and spin-ordered phases including ferro- and anti-ferromagnetic order along the cavity axis, which can be controlled via the pump strength and detuning. A real time observation of amplitude and phase of the emitted fields bears strong signatures of the realized phase and allows for real-time determination of phase transition lines. Together with measurements of the population imbalance most properties of the phase diagram can be reconstructed.