Investigating thermally robust spin entanglement of an atomic ⁸⁵Rb pair in an optical tweezer

Spin entangled states are of a high interest for performing non-classical calculations. Recently, entanglement generated by cold collisions of atomic ensembles were validated by HOM and Bell correlation experiments.. Isolating a single atomic pair using optical tweezers allows to investigate the spin-changing collision at the particle level and the resulting entangled state. However, this procedure has so far been successful only for groundstate-cooled atoms. Being able to maintain the coherence at a higher temperature would then be a step towards an engineering implementation. 

We study hot spin-changing collision as a route to entanglement and the parameters playing a role on the coherence of the prepared state. We observe the population dynamics of the magnetic sublevels of a atomic pair of ⁸⁵Rb undergoing a collision in an optical tweezer. The spin-changing collision of two thermal atoms initially prepared in m=0 in two microtraps leads to strong spin pair correlations between the states m=1 and m=-1. To distinguish between classical correlations or entanglement, we apply a Raman transition pulse coupling the two magnetic sublevels to probe the resulting pair spin state. The spin interaction during the 2-body collision depends on experimental parameters such as the depth of the trap, the bias magnetic field and the duration of the exchange. In the present investigation, we explore the role of those parameters and find the right tuning to leave the atom pair entangled by the spin-exchange collision.