Yvan Castin

Bose-Einstein Condensation in Atomic Gases

The discovery of the superfluid transition of liquid helium [1, 2] marked the first achievement of Bose–Einstein condensation in the laboratory, more than a decade after Einstein’s prediction for an ideal gas [3, 4]. Together with superconductivity, they o↵ered the first examples of macroscopic quantum phenomena and as such constituted a milestone in the history of Physics. The quest for the understanding of liquid helium superfluidity was the source of major advances in quantum many-body physics, such as the development of techniques inspired from quantum field theory and Landau’s phenomenological two-fluid model. The latter was in particular very successful for describing the hydrodynamics of this quantum liquid.

Unitary quantum three-body problem in a harmonic trap

We consider either 3 spinless bosons or 3 equal mass spin-1/2 fermions, interacting via a short range potential of infinite scattering length and trapped in an isotropic harmonic potential. For a zero-range model, we obtain analytically the exact spectrum and eigenfunctions: for fermions all the states are universal; for bosons there is a coexistence of decoupled universal and efimovian states. All the universal states, even the bosonic ones, have a tiny 3-body loss rate. For a finite range model, we numerically find for bosons a coupling between zero angular momentum universal and efimovian states; the coupling is so weak that, for realistic values of the interaction range, these bosonic universal states remain long-lived and observable.

Optimum Spin Squeezing in Bose-Einstein Condensates with Particle Losses

The problem of spin squeezing with a bimodal condensate in the presence of particle losses is solved analytically by the Monte Carlo wave function method. We find the largest obtainable spin squeezing as a function of the one-body loss rate, the two-body and three-body rate constants, and the s-wave scattering length.

Four-body Efimov effect for three fermions and a lighter particle.

We study three same-spin-state fermions of mass M interacting with a distinguishable particle of mass m in the unitary limit where the interaction has a zero range and an infinite s-wave scattering length. We predict an interval of mass ratio 13.384<M/m<13.607 where there exists a purely four-body Efimov effect, leading to the occurrence of weakly bound tetramers without Efimov trimers.

General relations for quantum gases in two and three dimensions. Two-component fermions

We derive exact relations for

Three-dimensional strong localization of matter waves by scattering from atoms in a lattice with a confinement-induced resonance

N

General relations for quantum gases in two and three dimensions. II. Bosons and mixtures

spin-1/2 fermions with zero-range or short-range interactions, in continuous space or on a lattice, in

A Monte Carlo formulation of the Bogolubov theory

2D

A wave function approach to dissipative processes

or in

Coherence properties of a continuous atom laser

3D