Physicists have developed a new optical centrifuge technique to control the rotation of molecules suspended in liquid helium nano-droplets. This advancement aims to further the understanding of exotic, frictionless superfluids.
The method represents the first demonstration of controlled spinning within a superfluid. Researchers can now directly manipulate the direction and frequency of a molecule's rotation, which is vital for studying how molecules interact with quantum environments at various rotational frequencies. The findings were published in the journal Physical Review Letters by researchers from the University of British Columbia (UBC) and the University of Freiburg.
Dr. Valery Milner, an associate professor at UBC Physics and Astronomy and lead author, highlighted the difficulty of controlling molecule rotation in any fluid due to interactions that effectively increase the molecule's resistance to spinning.
Superfluids, such as liquid helium, are states of matter at near-absolute zero temperatures that exhibit zero viscosity while still functioning as solvents. The current research focuses on exploring how solvated molecules are affected during the transition from a normal fluid to a quantum superfluid.
Traditional optical centrifuges, which spin molecules in gases using rotating laser pulses, had not been effective for molecules suspended in superfluids. Dr. Milner's team overcame this by embedding nitric oxide dimers in helium nano-droplets and introducing a short time delay between laser pulses. This created interference that resulted in a lower, constant rotation rate, thereby enhancing the molecules' "spinnability."
Using this new control over rotation frequency, the team plans to investigate a critical frequency point. Beyond this point, molecular rotation is expected to decay more rapidly due to the breakdown of superfluidity. Researchers aim to understand the specific conditions and frequencies at which this transition occurs at an atomic scale.
The Natural Sciences and Engineering Research Council of Canada, the Canada Foundation for Innovation, and the BC Knowledge Development Fund provided support for this research.