Direct observations of quantum vortices in helium II: Particle decoration and counterflow-induced waves

This dataset contains two videos recorded with the CryoLEM apparatus – see [1] and [2]. Images are captured using a global shutter sCMOS Andor Zyla 5.5 camera, with a pixel size of 6.7×6.7μm. The optical zoom is x0.97. The camera operates in the rotating frame, and illumination is achieved with a laser sheet perpendicular to the camera axis. 'Waves.avi' illustrates the wave propagation caused by counterflow in rotating helium II at 5 RPM. The video runs at real speed with a 10 Hz acquisition rate. The counterflow is generated by a heater at the channel's bottom filled with helium II—see [1] and [2]. This heater delivers a sinusoidal heat flux averaging 25 W/m² at 83.3 mHz, matching the rotation speed. The helium II temperature is maintained at 2.088K through controlled pumping. The vortex lattice, formed by steady rotation, is decorated with dihydrogen particles. Initially, the lattice remains mostly still, affected only slightly by residual flows. At 13:00, the heater activates, causing a smooth upward disturbance through the lattice affecting all particles, including those not on vortices. We observe vortex lines moving in and out of the laser sheet: illuminated vortex parts rise with the flow disturbance, creating bright streaks that indicate an out-of-plane component. 'Injection.avi' depicts the process of injecting dihydrogen particles into rotating liquid helium and their subsequent settlement on quantized vortices in helium II. The rotation speed is 10 RPM, and the current playback speed is shown in the top right corner. To better understand the video, the helium bath temperature is displayed below the video frames. All timestamps mentioned refer to the video timeline, not the temperature data. Initially, the helium bath temperature is just above the superfluid transition, with no particles in the bulk—only defocused bubbles visible. At 2:00, gaseous hydrogen is injected, condensing into a cloud of H2 particles that generate turbulence. As the temperature then drops, helium becomes superfluid at 19:00, marked as a reference point on the plot. This transition is evident as the cloudy appearance of the scene disappears, indicating the absence of bubbles. Turbulence gradually subsides, and some particles settle onto quantized vortices, forming straight segments. Once the fluid reaches solid-body rotation, the central vertical part of the image stabilizes, and the temperature is gradually lowered to the target value. With time increasing, this section widens, revealing straight, parallel vertical lines—vortices arranged in a lattice. Due to the high particle concentration used to make condensation visible, many particles do not settle on vortices, resulting in the formation of non-vertical filament clusters. Reference: [1] Peretti et al., Sci. Adv. 9, eadh2899 (2023) [2] Vessaire et al., arXiv:2510.00026 (2025)