Blocked populations in ring-shaped optical lattices

TL;DR

This paper investigates a unique dynamical regime in ring-shaped Bose-Einstein condensates where populations remain constant, yet persistent currents oscillate, revealing new insights into superfluid behavior in optical lattices.

Contribution

It introduces a novel dynamical regime with constant site populations and oscillating phases, distinct from self-trapping, supported by multimode and Gross-Pitaevskii simulations.

Findings

Persistent currents oscillate with a period determined by interaction energy.

Occupation numbers in each site remain constant during evolution.

Velocity circulation alternates between two values depending on the number of wells.

Abstract

We study a special dynamical regime of a Bose-Einstein condensate in a ring-shaped lattice where the populations in each site remain constant during the time evolution. The states in this regime are characterized by equal occupation numbers in alternate wells and non-trivial phases, while the phase differences between neighboring sites evolve in time yielding persistent currents that oscillate around the lattice. We show that the velocity circulation around the ring lattice alternates between two values determined by the number of wells and with a specific time period that is only driven by the onsite interaction energy parameter. In contrast to the self-trapping regime present in optical lattices, the occupation number at each site does not show any oscillation and the particle imbalance does not possess a lower bound for the phenomenon to occur. These findings are predicted with a multimode model and confirmed by full three-dimensional Gross-Pitaevskii simulations using an effective onsite interaction energy parameter.