Physics

Cold Atom Coupling

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Science  29 Jul 2005:
Vol. 309, Issue 5735, pp. 671
DOI: 10.1126/science.309.5735.671b

The ability to control the interaction strength between atoms within strongly interacting Fermi gases by sweeping a magnetic field across a Feshbach resonance provides a powerful experimental system in which to study many-body physics. One example is the crossover from a Bose-Einstein condensate (BEC) regime, in which the atoms are strongly coupled into pairs, to the weak-coupling regime that mimics Bardeen-Cooper-Schrieffer (BCS) coupling of electrons in superconducting metals. Although behavior on either side of the resonance is fairly well understood, of immediate interest is to find out what happens in the BEC-BCS crossover regime. However, determining the relative contributions of atom pairing mechanisms is an experimental and theoretical challenge.

Partridge et al.use a molecular spectroscopy technique to probe how the atoms pair up near the resonance. A laser is used to dress pairs of atoms and project them onto a known molecular energy level. Locking the excitation rate onto the molecular level allows them to make a precise measurement of the contribution of each pairing mechanism. The technique should prove useful for closer studies of the many-body physics involved in these cold atom systems. — ISO

Phys. Rev. Lett. 95, 020404 (2005).

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