Friction-enhanced lifetime of bundled quantum vortices

Experiments in the early 1980s have shown that a compact bundle of quantum vortex rings superfluid helium remains coherent and travels significant distance compared to its size. This is surprising because single ring, under effect friction with background thermal excitations (the so-called normal fluid), would quickly lose energy decay. The observation these long-lived structures has remained an unsettled question since their experimental detection. In this work, by taking into account fully coupled dynamics vortices fluid, we show motion generates large-scale wake fluid which reduces overall experienced bundle, enhancing lifetime. collective similar drag reduction observed systems active, hydrodynamically cooperative agents such as bacteria aqueous suspensions, fungal spores atmosphere cyclists pelotons.