Chiral Raman coupling for spin-orbit coupling in ultracold atomic gases

TL;DR

This paper introduces and experimentally demonstrates chiral Raman coupling to generate spin-orbit coupling in ultracold atomic gases, highlighting its direction-dependent properties and potential for topological quantum system simulation.

Contribution

It presents a novel chiral Raman coupling scheme for SOC in ultracold atoms, including 1D and 2D configurations, with experimental realization and comparison to nonchiral schemes.

Findings

Chiral Raman coupling exhibits high quantization axis direction dependence.

The scheme enables 1D and 2D SOC with chiral light-atom interactions.

Comparison shows differences between chiral and nonchiral SOC schemes.

Abstract

Spin-orbit coupling (SOC) in ultracold atoms is engineered by light-atom interaction, such as two-photon Raman transitions between two Zeeman spin states. In this work, we propose and experimentally realize chiral Raman coupling to generate SOC in ultracold atomic gases, which exhibits high quantization axis direction-dependence. Chiral Raman coupling for SOC is created by chiral light-atom interaction, in which a circularly polarized electromagnetic field generated by two Raman lasers interacts with two Zeeman spin states $\delta m_{F}=\pm 1$ (chiral transition). We present a simple scheme of chiral one-dimension (1D) Raman coupling by employing two Raman lasers at an intersecting angle 90$^{\circ}$ with the proper polarization configuration. In this case, Raman coupling for SOC exist in one direction of the magnetic quantization axis and disappears in the opposite direction. Then we extend this scheme into a chiral 2D optical square Raman lattice configuration to generate the 1D SOC. There are two orthogonal 1D SOC, which exists in the positive and negative directions of the magnetic quantization axis respectively. This case is compared with 2D SOC based on the nonchiral 2D optical Raman lattice scheme for studying the topological energy band. This work broadens the horizon for understanding chiral physics and simulating topological quantum systems.