Superfluidity of flexible chains of polar molecules

TL;DR

This paper investigates the superfluid properties of chains formed by polar molecules in layered optical lattices, revealing a quantum phase transition to a superfluid chain phase and establishing conditions for chain superfluidity.

Contribution

It introduces a theoretical framework and simulations demonstrating superfluidity of polar molecule chains and proves a theorem on chain length limitations.

Findings

Single chain exhibits quantum roughening transition.

Finite-density chains can undergo a transition to a superfluid phase.

Chains shorter than N cannot be superfluid.

Abstract

We study properties of quantum chains in a gas of polar bosonic molecules confined in a stack of N identical one- and two- dimensional optical lattice layers, with molecular dipole moments aligned perpendicularly to the layers. Quantum Monte Carlo simulations of a single chain (formed by a single molecule on each layer) reveal its quantum roughening transition. The case of finite in-layer density of molecules is studied within the framework of the J-current model approximation, and it is found that N-independent molecular superfluid phase can undergo a quantum phase transition to a rough chain superfluid. A theorem is proven that no superfluidity of chains with length shorter than N is possible. The scheme for detecting chain formation is proposed.