In situ observation of strongly interacting ferromagnetic domains in a shaken optical lattice

TL;DR

This paper demonstrates the creation of long-range ferromagnetic order in ultracold atoms within optical lattices by hybridizing Bloch bands, revealing spontaneous symmetry breaking and domain formation in a strongly interacting quantum system.

Contribution

It introduces a method to induce ferromagnetic order in ultracold atomic systems through band hybridization, advancing quantum simulation capabilities.

Findings

Observation of spontaneous symmetry breaking in bosonic condensates

Formation of sharp ferromagnetic domains with rapid equilibration

Quantum interference as the mechanism for symmetry breaking

Abstract

Solid state systems derive their richness from the interplay between interparticle interactions and novel band structures that deviate from those of free particles. Strongly interacting systems, where both of these phenomena are of equal importance, exhibit a variety of theoretically interesting and practically useful phases. Systems of ultracold atoms are rapidly emerging as precise and controllable simulators, and it is precisely in this strongly interacting regime where simulation is the most useful. Here we demonstrate how to hybridize Bloch bands in optical lattices to introduce long-range ferromagnetic order in an itinerant atomic system. We find spontaneously broken symmetry for bosons with a double-well dispersion condensing into one of two distinct minima, which we identify with spin-up and spin-down. The density dynamics following a rapid quench to the ferromagnetic state confirm quantum interference between the two states as the mechanism for symmetry breaking. Unlike spinor condensates, where interaction is driven by small spin-dependent differences in scattering length, our interactions scale with the scattering length itself, leading to domains which equilibrate rapidly and develop sharp boundaries characteristic of a strongly interacting ferromagnet.