Observation of quantized vortex in an atomic Bose-Einstein condensate at Dirac point with emergent spin-orbit coupling

TL;DR

This paper reports the direct observation of quantized vortices at the Dirac point in an atomic Bose-Einstein condensate with emergent spin-orbit coupling, revealing topological phenomena in a many-body quantum system.

Contribution

It demonstrates the first direct observation of vortices at a Dirac point in a quantum gas using a graphene-like optical lattice, advancing topological quantum physics research.

Findings

Quantized vortices observed at the Dirac point in a BEC.

Phase diagram of lattice bosons at the Dirac point mapped.

Method applicable to various topological optical lattices.

Abstract

When two or more energy bands become degenerate at a singular point in the momentum space, such singularity, or ``Dirac points", gives rise to intriguing quantum phenomena as well as unusual material properties. Systems at the Dirac points can possess topological charges and their unique properties can be probed by various methods, such as transport measurement, interferometry and momentum spectroscopy. While the topology of Dirac point in the momentum space is well studied theoretically, observation of topological defects in a many-body quantum systems at Dirac point remain an elusive goal. Based on atomic Bose-Einstein condensate in a graphene-like optical honeycomb lattice, we directly observe emergence of quantized vortices at the Dirac point. The phase diagram of lattice bosons at the Dirac point is revealed. Our work provides a new way of generating vortices in a quantum gas, and the method is generic and can be applied to different types of optical lattices with topological singularity, especially twisted bilayer optical lattices.