06 August 2014 Efimov trimers under strong confinement

An infinite series of Efimov trimers exist in 3D while only 2 survive in 2D. Here we study the crossover between these regimes.

Quasi-2D confinement turns a discrete scaling into a continuous one, and yields compounds with longer lifetimes In a paper published recently in Physical Review X, Dr. Pietro Massignan from the Quantum Optics Theory group led by ICREA Professor at ICFO Maciej Lewenstein, in collaboration with Drs. Jesper Levinsen (AIAS - Aarhus Institute for Advanced Studies) and Meera Parish (UCL - University College London) review the baffling properties of confined ultracold gases and theoretically show that strong confinement can be used to engineer more stable structures.

The dimensionality of a system can fundamentally impact the behavior of interacting quantum particles. Classic examples range from the fractional quantum Hall effect to high-temperature superconductivity. As a general rule, one expects confinement to favor the binding of particles. However, attractively interacting bosons apparently defy this expectation: While three identical bosons in three dimensions can support an infinite tower of Efimov trimers, only two universal trimers exist in the two-dimensional case. Here, we reveal how these two limits are connected by investigating the problem of three identical bosons confined by a harmonic potential along one direction. We show that the confinement breaks the discrete Efimov scaling symmetry and successively destroys the weakest bound trimers. However, the deepest bound trimers persist even under strong confinement. In particular, the ground-state Efimov trimer hybridizes with the two-dimensional trimers, yielding a superposition of trimer configurations that effectively involves tunneling through a short-range repulsive barrier. Our results suggest a way to use strong confinement to engineer more stable Efimov-like trimers, which have so far proved elusive.