For years, students have learned that there are four observable states of matter: solids, liquids, gases and plasma. But thanks to work by physicists from the University of Cambridge and the Oak Ridge National Laboratory, science textbooks might need to be updated with a brand-new phase of matter: “quantum spin liquid.”
After decades of searching, the researchers have uncovered the first piece of observable evidence for the elusive state, documented recently in Nature Materials. Here are three things to know about quantum spin liquid:
It’s not really a liquid
The “liquid” in “quantum spin liquid” is almost a misnomer. Unlike familiar liquids like water, here the word actually refers to how electrons behave under certain rare circumstances. All electrons have a property known as spin and can either spin up or down. In general, as a material’s temperature cools, its electrons tend to start spinning in the same direction. However, for materials in a quantum spin liquid state, the electrons never align. In fact, they actually become increasingly disordered, even at temperatures of absolute zero, Fiona MacDonald reports for Science Alert. It's this chaotic, flowing nature that spurred physicists to describe the state as “liquid.”
It makes electrons appear to split apart
Every atom in the universe is made of three particles: protons, electrons and neutrons. While physicists have found that protons and neutrons are composed of even smaller particles called quarks, so far electrons have been found to be indivisible. However, about 40 years ago theoretical physicists hypothesized that under certain circumstances, the electrons of certain materials can appear to split into quasiparticles called “Majorana fermions,” Sophie Bushwick writes for Popular Science.
Now, the electrons don’t actually break apart, they just act as if they do. But what’s really weird about Majorana fermions is that they can interact with each other on the quantum level as if they are actually particles. This odd property is what gives quantum spin liquids their disordered properties, as the interactions between Majorana fermions keep it from settling down into an orderly structure, Bushwick writes.
Unlike how the molecules of water become ordered as it freezes to ice, cooling the quantum spin liquid doesn't lead to any reduction in disorder.
Quantum spin liquids could help develop quantum computers
As powerful as modern computers can be, all of their operations boil down to encoding information as sequences of zeroes and ones. Quantum computers, on the other hand, could theoretically be vastly more powerful by encoding information using subatomic particles that can spin in multiple directions. That could allow quantum computers to run multiple operations at the same time, making them exponentially faster than normal computers. According to the study’s authors, Majorana fermions could one day be used as the building blocks of quantum computers by using the wildly spinning quasiparticles to perform all sorts of rapid calculations. While this is still a very theoretical idea, the possibilities for future experiments are exciting.