Observing Chiral Superfluid Order by Matter-Wave Interference

TL;DR

This paper demonstrates the spontaneous formation of chiral superfluid order in a Bose-Einstein condensate within an optical lattice, using matter-wave interference to directly observe phase properties and domain structures, highlighting the role of orbital degrees of freedom in quantum matter.

Contribution

It provides the first direct observation of chiral superfluid order in cold atoms and introduces a method to visualize phase and domain structures in optical lattices.

Findings

Direct observation of chiral order in BECs

Reconstruction of domain geometries

Role of orbital degrees in quantum matter

Abstract

The breaking of time reversal symmetry via the spontaneous formation of chiral order is ubiquitous in nature. Here, we present an unambiguous demonstration of this phenomenon for atoms Bose-Einstein condensed in the second Bloch band of an optical lattice. As a key tool we use a matter wave interference technique, which lets us directly observe the phase properties of the superfluid order parameter and allows us to reconstruct the spatial geometry of certain low energy excitations, associated with the formation of domains of different chirality. Our work marks a new era of optical lattices where orbital degrees of freedom play an essential role for the formation of exotic quantum matter, similarly as in electronic systems.