Light has been made into a strange material called a supersolid
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An odd solid that can flow like a fluid has been created from light for the first time. Studying it will help researchers better understand exotic quantum states of matter.
“We actually made light into a solid. That’s pretty awesome,” says Dimitris Trypogeorgos at the National Research Council (CNR) in Italy. He notes Daniele Sanvitto, also at CNR, showed how light could become a fluid more than a decade ago. Now Trypogeorgos, Sanvitto and their colleagues have used light to make not just any solid, but a quantum “supersolid”.
Supersolids simultaneously have zero viscosity and a crystal-like structure akin to the arrangement of atoms in salt crystals. These strange materials have no counterpart outside of the quantum realm. Because of this, they have previously only been created in experiments with atoms cooled to extremely low temperatures, where otherwise negligible quantum effects become dominant.
But in this experiment, the researchers replaced ultracold atoms with the semiconductor aluminium gallium arsenide and a laser.
They shone the laser onto a small piece of the semiconductor that had a pattern of narrow ridges. Complex interactions between the light and the material eventually formed a type of hybrid particle called a polariton. The ridge pattern constrained how these “quasiparticles” could move and what energies they could have in such a way that the polaritons formed a supersolid.
Sanvitto says the team had to very precisely measure enough properties of this trapped and transformed light to prove it was both a solid and a fluid with no viscosity. This was a challenge because scientists had never created and experimentally evaluated a supersolid made from light before, he says.
The new experiment contributes to physicists’ general understanding of how quantum matter can change its state by going through a phase transition, says Alberto Bramati at Sorbonne University in France. The team clearly demonstrated they made a supersolid, but many more measurements need to be done to understand its properties, he says.
Trypogeorgos says light-based supersolids may be easier to manipulate than those previously created with atoms, which could make his team’s experiment a first step towards understanding a slew of novel and surprising types of matter.
“We are really at the beginning of something new,” he says.
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