Topological phases in ultracold polar-molecule quantum magnets

TL;DR

This paper proposes using ultracold polar molecules in optical lattices to engineer customizable quantum spin models with topological phases, demonstrating the stability of these phases under realistic long-range interactions.

Contribution

It introduces a method to realize various quantum spin models with topological phases using microwave-dressed rotational states of polar molecules.

Findings

Symmetry protected topological phases are stabilized in spin ladders.

Topological phases persist with long-range dipolar interactions.

The approach enables realization of bilinear-biquadratic and Kitaev models.

Abstract

We show how to use polar molecules in an optical lattice to engineer quantum spin models with arbitrary spin S >= 1/2 and with interactions featuring a direction-dependent spin anisotropy. This is achieved by encoding the effective spin degrees of freedom in microwave-dressed rotational states of the molecules and by coupling the spins through dipolar interactions. We demonstrate how one of the experimentally most accessible anisotropies stabilizes symmetry protected topological phases in spin ladders. Using the numerically exact density matrix renormalization group method, we find that these interacting phases -- previously studied only in the nearest-neighbor case -- survive in the presence of long-range dipolar interactions. We also show how to use our approach to realize the bilinear-biquadratic spin-1 and the Kitaev honeycomb models. Experimental detection schemes and imperfections are discussed.