Frustrated magnets without geometrical frustration in bosonic flux ladders

TL;DR

This paper introduces a novel method to simulate frustrated magnetic systems using ultracold atoms in optical lattices, avoiding the need for geometrical frustration by leveraging synthetic dimensions and fluxes, revealing complex phases.

Contribution

It presents a new scheme to realize frustrated Bose-Hubbard models with synthetic dimensions, enabling exploration of frustrated magnetism without geometrical frustration.

Findings

Identification of bond-ordered-wave phases

Discovery of chiral superfluid phases

Mapping to an effective triangular ladder with flux

Abstract

We propose a scheme to realize a frustrated Bose-Hubbard model with ultracold atoms in an optical lattice that comprises the frustrated spin-1/2 quantum XX model. Our approach is based on a square ladder of magnetic flux close to $\pi$ with one real and one synthetic spin dimension. Although this system does not have geometrical frustration, we show that at low energies it maps into an effective triangular ladder with staggered fluxes for specific values of the synthetic tunneling. We numerically investigate its rich phase diagram and show that it contains bond-ordered-wave and chiral superfluid phases. Our scheme gives access to minimal instances of frustrated magnets without the need for real geometrical frustration, in a setup of minimal experimental complexity.