5. Theoretical Physics (CSN4)

Unitary gases

by Dr Yvan CASTIN (Laboratoire Kastler Brossel)

Aula Bruno Touschek (LNF)

Aula Bruno Touschek


Via Enrico Fermi, 40 00044 Frascati (Roma)
In cold atom experiments one can adjust at will the atomic interaction strength: with a simple application of a magnetic field, one can in principle tune the s-wave scattering length from minus infinity to plus infinity. For spin 1/2 fermions this has in particular led to the first observation of the crossover between a BCS state of Cooper pairs and a Bose-Einstein Condensate of dimers [1,2]. In this theoretical talk, we shall focus on the particularly fascinating case of an infinite scattering length. For spin 1/2 fermions, this leads to the so-called unitary gas, which was recently the subject of precise equation-of-state measurements/numerical calculations [3,4]. We shall review the intriguing physical consequences of scaling invariance of this maximally interacting gas, and make the link with Efimov physics: - mathematical representation by the Wigner-Bethe-Peierls (or zero-range) model [5] - dynamical consequences of the scaling invariant, and SO(2,1) hidden symmetry in a trap [6] - does the unitary gas really exist ? The threat of a generalized Efimov effect [7] - effect of mass imbalance between the two components: the single impurity problem, three-body [8] and four-body [9] Efimov effects - what about the mysterious ”unitary Bose gas” ?