The juggling soliton*

Non-propagating hydrodynamic solitons (NPHS) have been studied as prototypes of non-equilibrium localized structures. We have recently discovered a new combined structure: the juggling soliton. It is observed in a classical Faraday wave system were a NPHS exists, on top of which small drops of the same liquid can be stabilized, bouncing periodically for very long times, up to about an hour. We use distilled water with a few ml of photoflo and some drops of black ink. The NPHS can juggle one or more drops, typically of 3 mm diameter. These do not coalesce due to a thin layer of air that is continuously renewed at each rebound, as previously observed in bouncing drops below the Faraday instability. The soliton can juggle one or two drops on each side, with different equilibrium positions for each case: for a single drop this position is at the soliton’s center; for two drops, each one drifts a few mm away from the soliton’s center, finding new equilibrium positions. The NPHS is also able to handle three or four drops at once (two and one at each side and two on each side, respectively). For a single drop we present its stability diagram in terms of frequency and vibration amplitude, which is reduced with respect to the phase diagram of the NPHS alone.