Resonant Einstein-de Haas effect in a rubidium condensate

TL;DR

This paper demonstrates a resonant Einstein-de Haas effect in a rubidium condensate, where dipolar interactions cause transfer of atoms between Zeeman states and induce orbital angular momentum, with resonances amplifying the effect.

Contribution

The study numerically shows how dipolar interactions induce angular momentum transfer in rubidium condensates, revealing resonances that enhance the Einstein-de Haas effect.

Findings

Atoms transfer to other Zeeman states after magnetic field reversal.

Orbital angular momentum is generated in certain Zeeman states.

Resonances amplify the angular momentum transfer, making the effect observable.

Abstract

We numerically investigate a condensate of $^{87}$Rb atoms in an F=1 hyperfine state confined in an optical dipole trap. Assuming the magnetic moments of all atoms are initially aligned along the magnetic field we observe, after the field's direction is reversed, a transfer of atoms to other Zeeman states. Such transfer is allowed by the dipolar interaction which couples the spin and the orbital degrees of freedom. Therefore, the atoms in $m_F=0,-1$ states acquire an orbital angular momentum and start to circulate around the center of the trap. This is a realization of the Einstein-de Haas effect in systems of cold gases. We find resonances which amplify this phenomenon making it observable even in very weak dipolar systems. The resonances occur when the Zeeman energy on transfer of atoms to $m_F=0$ state is fully converted to the rotational kinetic energy.