Tunable dipolar resonances and Einstein-de Haas effect in a Rb-87 atoms condensate

TL;DR

This paper demonstrates tunable dipolar resonances and the Einstein-de Haas effect in a Rb-87 spinor condensate, showing how external magnetic fields can control atom transfer and angular momentum exchange.

Contribution

It introduces a method to selectively control dipolar interactions and atom transfer in Rb-87 condensates using magnetic field tuning.

Findings

Dipolar forces cause atom transfer between Zeeman states.

External magnetic fields enable resonance conditions for state transfer.

The system exhibits controllable angular momentum exchange.

Abstract

We study a spinor condensate of Rb-87 atoms in F = 1 hyperfine state confined in an optical dipole trap. Putting initially all atoms in mF = 1 component we observe a significant transfer of atoms to other, initially empty Zeeman states exclusively due to dipolar forces. Because of conservation of a total angular momentum the atoms going to other Zeeman components acquire an orbital angular momentum and circulate around the center of the trap. This is a realization of Einstein-de Haas effect in a system of cold gases. We show that the transfer of atoms via dipolar interaction is possible only when the energies of the initial and the final sates are equal. This condition can be fulfilled utilizing a resonant external magnetic field, which tunes energies of involved states via the linear Zeeman effect. We found that there are many final states of different spatial density which can be tuned selectively to the initial state. We show a simple model explaining high selectivity and controllability of weak dipolar interactions in the condensate of Rb-87 atoms.