Self-Organization in Cold Atoms Mediated by Diffractive Coupling

TL;DR

This paper explores how light-mediated feedback induces self-organization in cold atoms, leading to various ordered phases and magnetic states, with potential applications in quantum simulation and atomic crystallization.

Contribution

It introduces a novel mechanism of self-organization mediated by diffractive coupling and polarization control, extending understanding of atomic pattern formation and magnetic ordering.

Findings

Diffractive dephasing selects atomic lattice periods.

Spontaneous symmetry breaking occurs in 2D plane.

Coupling of internal Zeeman states leads to magnetic order.

Abstract

This article discusses self-organization in cold atoms via light-mediated interactions induced by feedback from a single retro-reflecting mirror. Diffractive dephasing between the pump beam and the spontaneous sidebands selects the lattice period. Spontaneous breaking of the rotational and translational symmetry occur in the 2D plane transverse to the pump. We elucidate how diffractive ripples couple sites on the self-induced atomic lattice. The nonlinear phase shift of the atomic cloud imprinted onto the optical beam is the parameter determining coupling strength. The interaction can be tailored to operate either on external degrees of freedom leading to atomic crystallization for thermal atoms and supersolids for a quantum degenerate gas, or on internal degrees of freedom like populations of the excited state or Zeeman sublevels. Using the light polarization degrees of freedom on the Poincar{\'e} sphere (helicity and polarization direction), specific irreducible tensor components of the atomic Zeeman states can be coupled leading to spontaneous magnetic ordering of states of dipolar and quadrupolar nature. The requirements for critical interaction strength are compared for the different situations. Connections and extensions to longitudinally pumped cavities, counterpropagating beam schemes and the CARL instability are discussed.