## Outline

We aim to explore physics frontiers that lie at the boarderlines between quantum physics, quantum measurement, information, thermodynamics, and machine learning. In particular, we exploit nonequilibrium open quantum physics and quantum thermodynamics by using ultracold atoms in which almost all parameters such as the interparticle interaction are tunable.

### Research Fields

Physics, Engineering, Mathematics, Multidisciplinary

### Keywords

Cold atoms

Bose-Einstein condensates

Nonequilibrium open quantum systems

Quantum thermodynamics

### Results

### Topological excitations in Bose-Einstein condensates

Bose-Einstein condensates offer a cornucopia of symmetry breaking because a rich variety of internal degrees of freedom are available depending on the atomic species. We have used these degrees of freedom to explore various aspects of symmetry breaking and topological excitations. Among them are the so-called Kibble-Zurek mechanism in which the order parameter develops singularities after some parameter of the system is suddenly quenched. Ordinary vortices and spin vortices are found to emerge. We also investigate novel topological phenomena such as knot excitations in an antiferromagnetic Bose-Einstein condensate.

Ground-state phase diagram of a spin-2 Bose-Einstein condensate (BEC). Depending on the phase, different topological excitations appear.