The spin Hall effect in a quantum gas

TL;DR

This paper demonstrates the observation of the spin Hall effect in a quantum-degenerate Bose gas, enabling the creation of a cold-atom spin transistor and advancing the potential for topological insulator research in quantum gases.

Contribution

It is the first to observe the spin Hall effect in a quantum gas and uses it to realize a cold-atom spin transistor with engineered spin-orbit coupling.

Findings

Successful measurement of spin-dependent Lorentz forces in a quantum gas

Realization of a laser-actuated analog to the Datta-Das spin transistor

Potential applications in magnetic and inertial sensors

Abstract

Electronic properties like current flow are generally independent of the electron's spin angular momentum, an internal degree of freedom present in quantum particles. The spin Hall effects (SHEs), first proposed 40 years ago, are an unusual class of phenomena where flowing particles experience orthogonally directed spin-dependent Lorentz-like forces, analogous to the conventional Lorentz force for the Hall effect, but opposite in sign for two spin states. Such spin Hall effects have been observed for electrons flowing in spin-orbit coupled materials such as GaAs or InGaAs and for laser light traversing dielectric junctions. Here we observe the spin Hall effect in a quantum-degenerate Bose gas, and use the resulting spin-dependent Lorentz forces to realize a cold-atom spin transistor. By engineering a spatially inhomogeneous spin-orbit coupling field for our quantum gas, we explicitly introduce and measure the requisite spin-dependent Lorentz forces, in excellent agreement with our calculations. This atomtronic circuit element behaves as a new type of velocity-insensitive adiabatic spin-selector, with potential application in devices such as magnetic or inertial sensors. In addition, such techniques --- for both creating and measuring the SHE --- are clear prerequisites for engineering topological insulators and detecting their associated quantized spin Hall effects in quantum gases. As implemented, our system realized a laser-actuated analog to the Datta-Das spin transistor.