Fig. 3. Sketch of the experiment and observables.
a After preparing an initial persistent current state with circulation w0, the n junctions are ramped up (see text). The 3D density plots are isosurfaces obtained from 3D GPE numerical simulations of the experimental set-up. If n is below a critical value nc depending on w0, the initial current is dissipated via the nucleation of vortices (here n = 2 and vortices are highlighted by orange cycling arrows in the upper right plot). Conversely, if n≥nc (here n = 4), the system remains stable with w = w0 (lower right plot). b Examples of experimental in-situ images and interferograms obtained for w0 = 2 and for the same number of junctions n as in (a): n = 2 (unstable configuration), at t = 0 (i), t = 1 ms (ii) and t = 7 ms (iii); and n = 4 (stable configuration) for t = 0 ms (iv), t = 1 ms (v) and t = 20 ms (vi). In the case (iii), the circulation has decayed (w(t) < w0) and the vortex emission is identified by the single spiral arm and the presence of a localized region of low density, i.e., a vortex.