Hannover 2020 – scientific programme

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Q: Fachverband Quantenoptik und Photonik

Q 10: Ultra-cold atoms, ions, and BEC II (joint session A/Q)

Q 10.6: Talk

Monday, March 9, 2020, 15:30–15:45, f303

Josephson junction dynamics in an ultracold two-dimensional Bose gas — •Vijay Singh and Ludwig Mathey — Zentrum für Optische Quantentechnologien and Institut für Laserphysik, Universität Hamburg, 22761 Hamburg, Germany

We investigate the Berezinskii-Kosterlitz-Thouless (BKT) scaling of the critical current of Josephson junction dynamics across a barrier potential in a two-dimensional (2D) Bose gas, motivated by recent experiments by Luick et al. arXiv:1908.09776. Using classical-field dynamics, we determine the dynamical regimes of this system, as a function of temperature and barrier height. As a central observable we determine the current-phase relation, as a defining property of these regimes. In addition to the ideal junction regime, we find a multimode regime, a second-harmonic regime, and an overdamped regime. For the ideal junction regime, we derive an analytical estimate for the critical current, which predicts the BKT scaling. We demonstrate this scaling behavior numerically for varying system sizes. The estimates of the critical current show excellent agreement to the numerical simulations and the experiments. Furthermore, we show the damping of the supercurrent due to phonon excitations in the bulk, and the nucleation of vortex-antivortex pairs in the junction.