Topologically induced avoided band crossing in an optical chequerboard lattice

TL;DR

This paper explores how topologically induced avoided band crossings in an optical chequerboard lattice affect bosonic condensates, revealing novel relaxation dynamics and symmetry changes during tuning.

Contribution

It demonstrates the experimental observation of topologically induced avoided crossings and their impact on condensate properties in an optical lattice.

Findings

Accelerated band relaxation near the avoided crossing

Condensate acquires finite momentum order and reduced symmetry

Landau-Zener oscillations characterize the crossing

Abstract

We report on the condensation of bosons in the 4th band of an optical chequerboard lattice providing a topologically induced avoided band crossing involving the 2nd, 3rd, and 4th Bloch bands. When the condensate is slowly tuned through the avoided crossing, accelerated band relaxation arises and the zero momentum approximately $C4$-invariant condensate wave function acquires finite momentum order and reduced $C2$ symmetry. For faster tuning Landau-Zener oscillations between different superfluid orders arise, which are used to characterize the avoided crossing.