Physicists have figured out how to spin molecules inside droplets of liquid helium using a custom optical centrifuge, which is exactly as cool and slightly absurd as it sounds. The team, led by researchers at the University of British Columbia (UBC) with help from the University of Freiburg, reports the first successful controlled rotation of a molecule inside a superfluid - a frictionless state of matter that flows without viscosity, basically the universe's way of showing off.

The optical centrifuge works by shooting rotating laser pulses at molecules embedded in helium nano-droplets. But unlike in gases, where this trick has been done before, superfluids put up a fight because dissolved molecules get gunked up with surrounding atoms. To solve this, the researchers doped the droplets with nitric oxide dimers and introduced a brief delay between laser pulses, creating a slower, steadier rotation that made the molecules more cooperative - what they call improved 'spinnability.'

"Controlling the rotation of a molecule dissolved in any fluid is a challenge," said Dr. Valery Milner, associate professor at UBC and author on the paper. "Imagine making a snowball: It's very easy to move it when it's small, but gets harder and harder as more snow gets attached to it." Fortunately, no snow was harmed in this experiment - just a lot of lasers and liquid helium at near absolute zero.

The work, published in Physical Review Letters, now lets researchers directly adjust both the direction and speed of a molecule's rotation, opening a new window into how molecules interact with their quantum surroundings. The team plans to vary the rotation frequency to find a critical point where superfluidity breaks down - because even frictionless matter has its limits. The research was funded by the Natural Sciences and Engineering Research Council of Canada, the Canada Foundation for Innovation, and the BC Knowledge Development Fund.