Striped gases

A story on: Spatial coherence of spin-orbit-coupled Bose gases (Phys. Rev. Lett. 124, 053605)

Background

Matter waves may interfere with each other provided they are “coherent”; i.e. that they maintain a well defined phase relation. Such coherent matter waves produce atomic density “ripples” or interference fringes when made to overlap. The contrast and duration of this interference pattern is subject to decoherence; the result of unwanted perturbations which modulate the phase randomly.

Coherent multi-spin (or spinor) gases will not render an interference pattern even if their motional state is exactly the same; for example if they originate from the same Bose-Einstein condensation trajectory, but when simultaneously dressed by an external coupling field such that the motional and spin degrees of freedom are coupled, a new phase of matter known as “stripe” phase is used to describe their ability to mix coherently.

Experiment

The experimental signature of spatial coherence is the presence of interference fringes, or stripes, and depends strongly on the coupling strength and inherent spinor miscibility (how homogeneous or heterogeneously will the two spins mix). In a fantastic effort led by A. Putra, we probe striped phases by using the stripes as a Bragg mirror so that by shining a laser at the right angle the reflected light beam allows us to detect, and even keep track of the spatial coherence in this gas.

Key finding

We observed stripe-phases that lived far longer than expected from decoherence, indicating better-than expected spatial coherence in our system.