# Spin Superfluidity versus Solidity of Ultracold Polar Molecules

## TL;DR

This paper proposes a method to engineer quantum magnets using ultracold polar molecules in optical lattices, revealing a novel interplay between spin superfluidity and solidity, and predicting the emergence of spin supersolid phases.

## Contribution

It introduces a technique to control spin interactions in ultracold molecules and explores the resulting exotic phases, including spin supersolids, through tunable dipole-dipole interactions.

## Key findings

- Control of inter-site interactions from antiferromagnetic to ferromagnetic.
- Prediction of spin supersolid phases in the system.
- Demonstration of the interplay between spin superfluidity and solidity.

## Abstract

We present a technique for engineering quantum magnets via ultracold polar molecules in optical lattices and explore exotic interplay between its spin superfluidity and solidity. The molecular ground and first excited rotational states are resonantly coupled by a linearly polarized microwave field. The spin-up (spin-down) states are presented by molecular rotational states of electric dipole moment along (against) the coupling field. By controlling the angle between the lattice direction and the coupling field, the inter-site interaction can be tuned from antiferromagnetic to ferromagnetic. Furthermore, the dipole-dipole interaction induces an exotic interplay between spin superfluidity and solidity, and spin supersolid phases may appear in mediate regions.