Witness Particles of Quantum Vortices express
In helium cooled to near absolute zero, the liquid stops rubbing against itself and begins to flow without any resistance. Physicists launched tiny polymer spheres (from one to six micrometers across, like bacteria) into such superfluid helium and tracked their fall through laser illumination. The spheres glowed, and a camera recorded their paths.
Some spheres descended smoothly, like grains of sand in thick syrup. Others suddenly jerked sideways, as if hitting invisible threads. These threads are quantum vortices: ultra-thin swirls where superfluidity tears like paper at a crease. Vortices arise from thermal jolts and persist even at 0.14 kelvin — two hundred times colder than a freezer.
When scientists looked at the motion of spheres along different segments of their paths, the picture changed. For the smallest particles, speeds split into two distinct peaks, like two floors in a building where some residents take the elevator and others run up the stairs. Larger spheres more often got stuck in tangled clumps of vortices and hung in the liquid for hours, even though by all laws they should have fallen. The physicists learned to count how many particles stuck to vortices and described their behavior with a simple equation, as if tallying passengers stuck on an escalator.
These glowing spheres are like probes thrown into an invisible storm. They show where the superfluid surface tears and how vortices latch onto matter. Such experiments help understand turbulence — a phenomenon that governs both weather and blood flow but remains a mystery to this day.
Original abstract
as written by the authors arXiv:2604.00707
An injection system for polymer particles, with diameters ranging from 1 to 6 $$\mu$$m, has been developed for visualizing flows in superfluid $$^4$$He at temperatures down to 0.14 K. Using an ultrasound transducer, bursts of particles were launched into a sample of superfluid and allowed to descend under gravity. The particles were imaged using their fluorescence in the presence of a sheet of laser light. We report on the statistical behavior of particles during their descent, including descriptions of a mixture of smooth and erratic trajectories, indicative of the interactions with thermal excitations and quantized vortex lines. Temperature-dependent velocity distributions were measured and analyzed, yielding Gaussian distributions with power law tails persisting into the zero temperature limit. When sampled over increasing length scales, these distributions bifurcated into exponential for the smallest particles and bimodal Gaussian for the largest. We also report observations of long-lived suspensions of small particles at temperatures near 1 K, which appear to be associated with the trapping of large numbers of particles in a turbulent vortex tangle. A method was developed for identifying and quantifying the numbers of particles bound to vortex lines, allowing for a description of the temporal dynamics of their population by an analytical model.
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