Thursday, July 26, 2007

Atoms Swap Spins

This is another rather cool experiment (pun intended) published in this week's Nature[1]. They have managed to "swap" spin states between cold Rb atoms.

Anderlini et al. find a way to make use of a similar symmetry-based constraint. They work with bosonic rubidium atoms, 87Rb, that have a symmetric total wavefunction. This wavefunction has two components: a spin component describing the internal state of the atoms, and a spatial component describing their locations. Because of the fixed exchange symmetry of the total wavefunction, the symmetries of the spin and spatial wavefunctions are precisely related: if the spin wavefunction for 87Rb atoms is symmetric, then the spatial wavefunction is also symmetric, and vice versa. Crucially, antisymmetric spatial wavefunctions hinder particles from getting close to each other, whereas symmetric spatial wavefunctions favour it. Because the atoms interact effectively only when they come into contact, particles in symmetric spatial states interact with each other, whereas particles in antisymmetric spatial states do not.

Anderlini et al. stored quantum information in the atoms' spin wavefunction, such that the stored bits determined its symmetry character — symmetric, antisymmetric or a superposition of both. The spin wavefunction also controlled the spatial wavefunction through the direct link between their symmetries, and so determined the collisional properties. Thus, the state of the quantum bits controlled the atoms' interactions.

Also read the News and Views review in the same issue of Nature, and also a report on this work on PhysicsWeb.


[1] M. Anderlini et al. Nature v.448, p.452 (2007).

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