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Physical Review Letters

Universal Critical Dynamics of Vortex Shedding in Quantum Fluids

Anonymous, Francesco Viola, Paolo Luchini, Vincenzo Citro

Published Jun 25, 2026• 0 citations
Publisher

Abstract

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.

DOI
10.1103/pd91-32q3

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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.
We report on the experimental observation of vortex cluster shedding from a moving obstacle in an oblate atomic Bose-Einstein condensate. At low obstacle velocities v above a critical value, vortex clusters consisting of two like-sign vortices are generated to form a regular configuration like a von Kármán street, and as v is increased, the shedding pattern becomes irregular with many different kinds of vortex clusters. In particular, we observe that the Stouhal number associated with the shedding frequency exhibits saturation behavior with increasing v. The regular-to-turbulent transition of the vortex cluster shedding reveals remarkable similarities between a superfluid and a classical viscous fluid. Our work opens a new direction for experimental investigations of the superfluid Reynolds number characterizing universal superfluid hydrodynamics.
We report on the experimental observation of vortex cluster shedding from a moving obstacle in an oblate atomic Bose-Einstein condensate.At low obstacle velocities v above a critical value, vortex clusters consisting of two like-sign vortices are generated to form a regular configuration like a von Kármán street, and as v is increased, the shedding pattern becomes irregular with many different kinds of vortex clusters.In particular, we observe that the Stouhal number associated with the shedding frequency exhibits saturation behavior with increasing v.The regular-to-turbulent transition of the vortex cluster shedding reveals remarkable similarities between a superfluid and a classical viscous fluid.Our work opens a new direction for experimental investigations of the superfluid Reynolds number characterizing universal superfluid hydrodynamics.
Two-dimensional flow past an infinitely long cylinder of nanoscopic radius in superfluid 4He^{4}\mathrm{He}4He at zero temperature is studied using time-dependent density-functional theory. The calculations reveal two distinct critical phenomena for the onset of dissipation: (i) vortex-antivortex pair shedding from the periphery of the moving cylinder, and (ii) the appearance of cavitation in the wake, which possesses similar geometry to that observed experimentally for fast-moving micrometer-scale particles in superfluid 4He^{4}\mathrm{He}4He. The formation of cavitation bubbles behind the cylinder is accompanied by a sudden jump in the drag exerted on the moving cylinder by the fluid. Vortex pairs with the same circulation are occasionally emitted in the form of dimers, which constitute the building blocks for the Benard--von Karman vortex street structure observed in classical turbulent fluids and Bose-Einstein condensates. The cavitation-induced dissipation mechanism should be common to all superfluids that are self-bound and have a finite surface tension, which include the recently discovered self-bound droplets in ultracold Bose gases. These systems would provide an ideal testing ground for further exploration of this mechanism experimentally.
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In quantum fluids, the quantization of circulation forbids the diffusion of a vortex swirling flow seen in classical viscous fluids. Yet, accelerating quantum vortices may lose their energy into acoustic radiations(1,2), similar to the way electric charges decelerate on emitting photons. The dissipation of vortex energy underlies central problems in quantum hydrodynamics(3), such as the decay of quantum turbulence, highly relevant to systems as varied as neutron stars, superfluid helium and atomic condensates(4,5). A deep understanding of the elementary mechanisms behind irreversible vortex dynamics has been a goal for decades(3,6), but it is complicated by the shortage of conclusive experimental signatures(7). Here we address this challenge by realizing a programmable vortex collider in a planar, homogeneous atomic Fermi superfluid with tunable inter-particle interactions. We create on-demand vortex configurations and monitor their evolution, taking advantage of the accessible time and length scales of ultracold Fermi gases(8,9). Engineering collisions within and between vortex-antivortex pairs allows us to decouple relaxation of the vortex energy due to sound emission and that due to interactions with normal fluid (that is, mutual friction). We directly visualize how the annihilation of vortex dipoles radiates a sound pulse. Further, our few-vortex experiments extending across different superfluid regimes reveal non-universal dissipative dynamics, suggesting that fermionic quasiparticles localized inside the vortex core contribute significantly to dissipation, thereby opening the route to exploring new pathways for quantum turbulence decay, vortex by vortex.By controlling the generation and collision of individual vortices in atomic Fermi superfluids, a study provides a comprehensive view of vortex decay due to mutual friction and vortex-sound interaction.
Reconnections of coherent filamentary structures play a key role in the dynamics of fluids, redistributing energy and helicity among the length scales, triggering dissipative effects, and inducing fine-scale mixing. Unlike ordinary (classical) fluids where vorticity is a continuous field, in superfluid helium and in atomic Bose-Einstein condensates (BECs) vorticity takes the form of isolated quantized vortex lines, which are conceptually easier to study. New experimental techniques now allow visualization of individual vortex reconnections in helium and condensates. It has long being suspected that reconnections obey universal laws, particularly a universal scaling with time of the minimum distance between vortices δ. Here we perform a comprehensive analysis of this scaling across a range of scenarios relevant to superfluid helium and trapped condensates, combining our own numerical simulations with the previous results in the literature. We reveal that the scaling exhibits two distinct fundamental regimes: a [Formula: see text] scaling arising from the mutual interaction of the reconnecting strands and a [Formula: see text] scaling when extrinsic factors drive the individual vortices.