Dynamical Phase Diagram of Ultracold Josephson Junctions.

In Josephson junctions with ultracold atoms, the Josephson current can be driven by a chemical potential difference across the junction, which can be present due to nonlinear interactions and for a non-zero population imbalance z(t) between the two wells. Depending on the value of the initial imbalance z₀ different dynamical regimes could be found. In fact, if z₀ is smaller than a critical value z_cr the system enters the  `plasma' regime. When z₀ instead exceeds z_cr, different experimental studies observed a transition either to self-trapping (as e.g. Ref.~[1]), or to a dissipative regime (as e.g. Ref.~[2]). These findings raise the interesting question of what distinguishes between such transitions/regimes, and whether a particular experimental set-up could be found that would allow for all three regimes to be observed.

In this talk, we provide a complete study of the phase diagram emerging in a three-dimensional Josephson junction composed of two Bose-Einstein condensates of molecules of ⁶Li, which are coupled through a barrier [3-4]. In particular, we show the presence of all three dynamical regimes upon careful control of the barrier height, width and z₀. Moreover, our work connects the role of the barrier, vortex rings and associated acoustic emission with different regimes of the superfluid dynamics across the junction.

References:

[1] M. Albiez et al., PRL 95, 010402(2005).

[2] G. Valtolina et al., Science 350,1505 (2015).

[3] K. Xhani et al., PRL 124, 045301 (2020).

[4] K. Xhani et al., NJP 22, 123006 (2020).