Sharp Corners Break Superfluidity express
A superfluid flows without friction, like water in a perfectly smooth pipe, but the moment it hits an obstacle, the picture changes. In a new study, researchers looked at how a superfluid stream flows around rectangular walls and pits with sharp corners. It turns out that right at the corners, the flow speed jumps dramatically, like air over an airplane wing, only stronger. This acceleration, not the overall flow speed, decides when vortices, tiny quantized whirlpools, are born in the fluid.
Using a mathematical method that traces back to the work of Hermann Schwarz, the authors derived exact formulas for the critical speed — the speed at which vortices start to appear. The formulas depend only on the obstacle's width and its height or depth. Numerical simulations confirmed the theory with high precision. This means you can predict in advance at what speed a superfluid flow will lose stability, simply by measuring the obstacle's dimensions.
The results apply directly to experiments with Bose-Einstein condensates — clouds of atoms cooled to near absolute zero, where superfluidity is observed in the lab. There, obstacles with sharp edges are created with laser beams, and now one can more accurately calculate when vortices will appear. This is a step toward controlling quantum vortices — which could become components of future quantum devices.
Original abstract
as written by the authors arXiv:2602.18876
We investigate analytically and numerically the dynamics of a two-dimensional superflow governed by the Gross-Pitaevskii equation passing over finite-size rectangular obstacles: an impenetrable wall and an impenetrable rectangular well. Extending classical studies of vortex nucleation around smooth obstacles, we focus on the role of sharp corners in determining the onset of vortex nucleation. Using a combination of analytical techniques based on the Schwarz-Christoffel methods for potential flow and on numerical simulations, we show that local velocity amplification near sharp corners crucially controls the critical flow velocity for vortex nucleation. For both wall and well configurations, we identify analytically and theoretically the critical velocities as a function of the obstacle width and its height or depth, finding an excellent agreement between the theory and our numerical simulations. Our results provide a simple framework for understanding superflow stability past finite-size obstacles with sharp features and are directly relevant to experimentally realizable configurations in atomic Bose-Einstein condensates and related superfluid systems.
Quantized vortices in superfluid helium were first seen in the 1950s by shooting a beam of electrons through the liquid, the vortices cast shadows like tiny tornadoes.