Universal Critical Dynamics of Vortex Shedding in Quantum Fluids.

In classical fluid dynamics, the von Kármán vortex street behind a bluff body is the canonical example used to study vortex formation and dynamics. This is governed by a local Hopf bifurcation, which drives the continuous and asynchronous release of vortical structures in the wake. In superfluid systems, however, the quantization of vorticity fundamentally alters this picture. Several aspects of quantum vortex shedding remain unresolved, including the absence of a unified description spanning the pre- and post-threshold regimes. We show that the onset of vortex emission is governed by a global saddle node on invariant circle bifurcation. This mechanism produces a discrete transition characterized by a macroscopic bottleneck in phase space and a universal inverse-square-root divergence of the emission period near the critical velocity. These features are robust across obstacles of different shapes, revealing a universal mechanism underlying vortex shedding in quantum fluids.