"The analyses of the images shows that a surprising number of drops were not spherical as expected, but were pulled length-wise by rapid rotation," says Rolles. "In fact, some drops possessed more of a shape resembling a thick wheel with two almost parallel sides." The rotation stems from the expansion of the liquid helium inside the nozzle, through which they enter the experimental chamber. The droplets rotated up to fourteen million times per second far faster than a normal round drop could withstand according to the laws of classical physics.
Due to the rapid rotation, tiny "quantum vortices" formed within the nanodroplets, reminiscent of a miniature whirlpool swirling around a bathtub drain. This phenomenon had already been observed in larger units of superfluid helium, but has just now been detected in nanodroplets for the first time. As observed earlier, the vortices form a regular lattice. "In nanodroplets, the quantum vortices are surprisingly 100,000 times more densely packed than in the larger samples of superfluid helium that were previously studied," says Vilesov.
"What we have observed in this experiment is really surprising," stresses co-lead Christopher Bostedt of SLAC. The experiment's third co-lead, Oliver Gessner from the Lawrence Berkeley National Laboratory, adds: "Now that we have shown that we can detect and characterize quantum rotation in helium nanodroplets, it will be important to understand its origin and, ultimately, to try and control it."
|Contact: Thomas Zoufal|
Deutsches Elektronen-Synchrotron DESY