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arXiv:1405.5525

Optimization as a route towards observing the Einstein-de Haas effect in a rubidium condensate

Tomasz Świsłocki, Mariusz Gajda, Mirosław Brewczyk

Published May 21, 2014• 0 citations
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Abstract

The main obstacle in experimental realization of the Einstein-de Haas effect in a Bose-Einstein condensate is necessity of a very precise control of the extremely small (of the order of tens of $μ$G) external magnetic field. In this paper we numerically study the response of a rubidium condensate to an optimized time-dependent magnetic field. We find a significant transfer of atoms from the initial maximally polarized state to the next Zeeman component at magnetic fields of the order of tens of milligauss. We propose an experiment in which such an optimization scheme could enable the observation of the Einstein-de Haas effect in a rubidium atom condensate.

DOI
10.48550/arxiv.1405.5525

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The main obstacle in experimental realization of the Einstein-de Haas effect in a Bose-Einstein condensate is necessity of a very precise control of the extremely small (of the order of tens of μμμG) external magnetic field. In this paper we numerically study the response of a rubidium condensate to an optimized time-dependent magnetic field. We find a significant transfer of atoms from the initial maximally polarized state to the next Zeeman component at magnetic fields of the order of tens of milligauss. We propose an experiment in which such an optimization scheme could enable the observation of the Einstein-de Haas effect in a rubidium atom condensate.
The main obstacle in the experimental realization of the Einstein--de Haas effect in a Bose-Einstein condensate is the need for very precise control of the extremely small (of the order of tens of $\ensuremath{\mu}\mathrm{G}$) external magnetic field. In this paper, we numerically study the response of a rubidium condensate to a magnetic field that is linearly dependent on time. We find a significant transfer of atoms from the initial maximally polarized state to the next Zeeman component at magnetic fields of the order of tens of milligauss. We propose an experiment in which such a time-dependent magnetic-field-based scheme could enable the observation of the Einstein--de Haas effect in a rubidium atom condensate.
Einstein-de Haas effect for a 87^{87}87Rb atoms condensate
We consider a condensate of 87^{87}87Rb 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 due to the dipolar interaction. We find that there exist resonances which amplify the effect of dipolar interaction. When the resonance condition is satisfied the transfer of atoms to mF=0,−1m_F=0,-1mF​=0,−1 states might be of the order of the initial population of mF=1m_F=1mF​=1 component. While changing the magnetic moments during the transfer, the atomsacquire an orbital angular momentum and start to circulate around the center of the trap. This is a realization of the famous Einstein-de Haas effect in systems of cold gases. Due to the dipolar resonances, it becomes possible to observe this phenomenon even in a condensate of 87^{87}87Rb (F=1) atoms that have very small magnetic moment.
We numerically investigate a condensate of 87Rb 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. The atoms in m_F=0, −1 start to circulate around the center of the trap. We find resonances which amplify this phenomenon making it observable even in rubidium condensates.
We theoretically study a spinor condensate of 87Rb^{87}\mathrm{Rb}87Rb atoms in a F=1F=1F=1 hyperfine state confined in an optical dipole trap. Putting initially all atoms in an mF=1{m}_{F}=1mF​=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 the Einstein-de Haas effect in a system of cold gases. We show that the transfer of atoms via dipolar interactions 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 87Rb^{87}\mathrm{Rb}87Rb atoms.
We theoretically consider a spin polarized, optically trapped condensate of 87Rb atoms in F=1. We observe a transfer of atoms to other Zeeman states due to the dipolar interaction which couples the spin and the orbital degrees of freedom. Therefore the transferred atoms acquire an orbital angular momentum. This is a realization of the Einstein-de Haas effect in systems of cold gases. We find resonances which make this phenomenon observable even in very weak dipolar systems, when the Zeeman energy difference on transfer is fully converted to rotational kinetic energy.
We propose an experiment which proves the possibility of spinning gaseous media via dipolar interactions in the spirit of the famous Einstein-de Haas effect for ferromagnets. The main idea is to utilize resonances that we find in spinor condensates of alkali atoms while these systems are placed in an oscillating magnetic field. A significant transfer of angular momentum from spin to motional degrees of freedom observed on resonance is a spectacular manifestation of dipolar effects in spinor condensates.