Quantum rotor model for a Bose-Einstein condensate of dipolar molecules

TL;DR

This paper introduces a quantum rotor model for a Bose-Einstein condensate of dipolar molecules under small electric fields, revealing multiple phases and quantum effects like squeezing.

Contribution

It presents an exact solution of the quantum rotor model, uncovering new many-body phases and quantum properties of the macroscopic dipole moment in dipolar molecular BECs.

Findings

Identifies symmetric, dipolar, and nematic phases in the system.

Shows quantum squeezing of the angular momentum distribution.

Reveals many-body effects leading to nematic phases.

Abstract

We show that a Bose-Einstein condensate of heteronuclear molecules in the regime of small and static electric fields is described by a quantum rotor model for the macroscopic electric dipole moment of the molecular gas cloud. We solve this model exactly and find the symmetric, i.e., rotationally invariant, and dipolar phases expected from the single-molecule problem, but also an axial and planar nematic phase due to many-body effects. Investigation of the wavefunction of the macroscopic dipole moment also reveals squeezing of the probability distribution for the angular momentum of the molecules.