Spin-orbit coupling in the presence of strong atomic correlations

TL;DR

This paper investigates how contact interactions influence a two-atom ultracold system with synthetic spin-orbit coupling, revealing unique few-particle ground states and entanglement behaviors not seen in mean-field regimes.

Contribution

It demonstrates the emergence of a novel anti-symmetric spin state in a bosonic system due to competing interactions, specific to few-particle regimes.

Findings

Ground state contains significant anti-symmetric spin contribution.

Transition characterized by inversion of average momentum.

Pseudo-spin entanglement is strongly suppressed by spin-orbit coupling.

Abstract

We explore the influence of contact interactions on a synthetically spin-orbit coupled system of two ultracold trapped atoms. Even though the system we consider is bosonic, we show that a regime exists in which the competition between the contact and spin-orbit interactions results in the emergence of a ground state that contains a significant contribution from the anti-symmetric spin state. This ground state is unique to few-particle systems and does not exist in the mean-field regime. The transition to this state is signalled by an inversion in the average momentum from being dominated by centre-of-mass momentum to relative momentum and also affects the global entanglement shared between the real- and pseudo-spin spaces. Indeed, competition between the interactions can also result in avoided crossings in the groundstate which further enhances these correlations. However, we find that correlations shared between the pseudo-spin states are strongly depressed due to the spin-orbit coupling and therefore the system does not contain spin-spin entanglement.