PARIS: Scientists on Wednesday said that they have successfully stirred a strange matter called a “supersolid” — which is both rigid and fluid — for the first time, providing direct proof of the dual nature of this quantum oddity.
In everyday life, there are four states of matter — solid, liquid, gas and the rarer plasma.
But physicists have long been investigating what are known as “exotic” states of matter, which are created at incredibly high energy levels or temperatures so cold they approach absolute zero (-273.15 degrees Celsius or -459.67 degrees Fahrenheit).
Under these extreme conditions, matter starts behaving very differently from what we are used to.
Fluids such as liquid or gas may get more or less resistance to flow, which is measured by viscosity. Honey, for example, is more viscous than water.
Superfluids, an extremely cold exotic matter, have zero viscosity — there is no resistance so they flow freely.
If a superfluid was stirred in a cup, it would flow around indefinitely without ever slowing down.
More than half a century ago, physicists predicted the existence of a “supersolid” state.
It is matter that has the properties of both a solid and a superfluid, in which a fraction of the atoms flow friction-free through the lattice — a regular arrangement of points or objects — of a rigid crystal structure.
Researchers had previously managed to observe these crystal structures inside supersolids in several ways.
But a direct observation of the bizarre manner in which this matter flows has remained elusive, said Francesca Ferlaino, a physicist at Austria’s University of Innsbruck.
Until a new study led by Ferlaino was published in the journal Nature on Wednesday.
The team managed to stir a supersolid to observe the tiny whirlpools — called quantised vortices — which are the “smoking gun of superfluidity”, Ferlaino told AFP.
“Imagine you have a cup of coffee, and you give it a little swirl with a spoon,” she explained.
“You’ll see the coffee spinning around the centre, and if you look closely, there might be a whirlpool in the middle where the liquid is swirling the fastest. This is a classic example of a vortex in a regular fluid.”
Now imagine the coffee is replaced with a superfluid.
“If you swirl the spoon slowly, you’ll be surprised to see that the superfluid doesn’t rotate along with the spoon at all — it remains perfectly still, as if nothing disturbed it,” Ferlaino said.
“However, if you swirl the spoon faster, instead of forming one large whirlpool in the centre, something remarkable happens.