The Molecular Component in Collisions in a Dense BEC

Bas van de Meerakker

Matteo Rini

Dense ensembles of laser-cooled molecules allow the observation of molecular collisions—a result that could lead to applications of cold molecular gases in quantum simulation and fundamental physics tests.

Fang Fang

Ultracold atomic system provides us a versatile platform to address problems ranging from quasi-particle excitations supported by a variety of ground states, to cold collisions which could lead to a precise determination of interatomic molecular potential, and to atomtronics focusing on atomic analogues of electronic components. In this dissertation, I describe our efforts in exploring a wide topic range by our \\Rb Bose Einstein condensate (BEC) machine and \\Li - \\Rb mixture machine, including magnons, which are collective spin excitations supported by Rb F = 1 ferromagnetic BEC ground state, cold elastic collisions between Li and Rb co-trapped in a spherical quadrupole trap, and Li spin dynamics in a spin bath formed by Rb.

Jeremy M. Hutson

Aaron James Sup

Roman Bause, Arthur Christianen, Andreas Schindewolf +2 more

Collisional complexes, which are formed as intermediate states in molecular collisions, are typically short-lived and decay within picoseconds. However, in ultracold collisions involving bialkali molecules, complexes can live for milliseconds, completely changing the collision dynamics. This can lead to unexpected two-body loss in samples of nonreactive molecules. During the past decade, such "sticky" collisions have been a major hindrance in the preparation of dense and stable molecular samples, especially in the quantum-degenerate regime. Currently, the behavior of the complexes is not fully understood. For example, in some cases, their lifetime has been measured to be many orders of magnitude longer than recent models predict. This is not only an intriguing problem in itself but also practically relevant, since understanding molecular complexes may help to mitigate their detrimental effects. Here, we review the recent experimental and theoretical progress in this field. We treat the case of molecule-molecule as well as molecule-atom collisions.