Experiments

Experiments with ultra-cold atoms: study of defects across phase transitions

We study the mechanism of spontaneous production of defects across the BEC transition in an ultracold Sodium gas.
The Kibble-Zurek mechanism is responsible for the creation of parts of the system with different order parameter and therefore for the existence of defects in the condensate, such as solitons or vortices.
In our elongated BEC, solitons should quickly decay into a more stable defect called solitonic vortex, a vortex oriented along the short axis of the cigar-like BEC, characterized by a density depletion in the radial plane that contains it.
We observed and charcterized such exotic phase defect and aim to study its dynamics in time, by observing its motion and its possible interaction and reconnection with other defects, a phenomenon at the basis of quantum turbulence.

A condensate of Sodium atoms is formed by quenching the temperature across the BEC phase transition. If the quench is fast, defects appear in the order parameter due to the Kibble-Zurek mechanism.

Tri-axial absorption imaging of elongated BECs after a long time of flight providing clear signatures of the presence of solitonic vortices with opposite circulation.