Quantized Vortex States of Strongly Interacting Bosons in a Rotating Optical Lattice

TL;DR

This paper investigates the behavior of strongly interacting bosons in rotating optical lattices, revealing vortex entry, quantum phase transitions, and the role of quasi-angular momentum in systems with broken rotational symmetry.

Contribution

It introduces the concept of quasi-angular momentum to characterize vortex states and quantum phase transitions in lattice systems with broken rotational symmetry.

Findings

Maximum of L-1 vortices in an LxL lattice

Energy level crossings signal quantum phase transitions

Quasi-angular momentum captures discrete rotational symmetry

Abstract

Bose gases in rotating optical lattices combine two important topics in quantum physics: superfluid rotation and strong correlations. In this paper, we examine square two-dimensional systems at zero temperature comprised of strongly repulsive bosons with filling factors of less than one atom per lattice site. The entry of vortices into the system is characterized by jumps of 2 pi in the phase winding of the condensate wavefunction. A lattice of size L X L can have at most L-1 quantized vortices in the lowest Bloch band. In contrast to homogeneous systems, angular momentum is not a good quantum number since the continuous rotational symmetry is broken by the lattice. Instead, a quasi-angular momentum captures the discrete rotational symmetry of the system. Energy level crossings indicative of quantum phase transitions are observed when the quasi-angular momentum of the ground-state changes.