Physicists Achieve World-First Creation of a Supersolid Made of Light

The gap between science fiction and science fact seems to be closing more rapidly every single day lately. For example, researchers recently transformed light into a crystalline structure that combines properties of both a superfluid and a solid, known as a “supersolid”. The idea of a supersolid was first theoretically predicted in the 1960s. However, it was only in 2017 that scientists successfully created supersolids using ultracold dipolar gases in optical traps. This latest attempt, though, was the first time they had succeeded in coupling matter and light to produce a supersolid. This has significantly cleared the way for the study of condensed matter physics.

Understanding Supersolids 

In quantum mechanics, a supersolid is defined as a state of matter where the particles condense into a crystalline solid, yet move like a liquid without any friction, a typical characteristic of superfluids. Solids don’t usually move on their own accord. However,  supersolids are able to change their density and direction based on their interactions with particles while retaining a lattice structure. They only form at extremely low temperatures since heat will make the particles jump around. At absolute zero, heat no longer interferes with how particles interact and instead starts behaving based on the effects of quantum mechanics. With the exception of supersolids and superfluids, all fluids possess some degree of viscosity. 

A fluid with a higher viscosity sticks to itself more and therefore tends to resist movement. The most well-known example of a viscosity-less fluid is helium cooled at ultra-low temperatures. At absolute zero, particles are typically not completely still due to the uncertainty principle, so they still move around slightly. However, when it comes to helium-4 isotopes, the particles still move around considerably. In fact, one would have to apply 25 atmospheres of pressure to stop the particles moving and for the helium-4 isotope to become solid. Quantum phenomena such as helium-4’s movement at absolute zero significantly impact how fluids act. For example, they lose viscosity and therefore they lose all friction. 

How Scientists Turned Light Into a Supersolid

The researchers started by directing light from a laser onto a customized semiconductor material called gallium arsenide. This resulted in the formation of polaritons – quasiparticles that are hybrids of photons and excitons. To achieve the supersolid state, the researchers then confined the polaritons within a photonic crystal waveguide. The polaritons then condense into a bound state, resulting in the spontaneous self-organization of the polaritons into a crystalline structure. 

While previous methods relied on ultracold atomic gases, this new approach uses the coupling of light-matter in semiconductor nanostructures. This offers researchers a unique platform for the exploration of the quantum phases of matter. The more we learn about supersolids, the more we understand how particles and atoms are put together. This could potentially lead to advances in light-emitting devices, frictionless lubricants, and neuromorphic computing. With every new breakthrough, we lay down the foundations to build the bridge between fundamental science and beneficial practical applications. 

At its core, this breakthrough is a shining example of how techniques we once considered science fiction are fast becoming reality. The theory of manipulating light to become a flowing yet structured form once seemed impossible, yet now it is an observable phenomenon. The better we understand this phenomenon, the closer we are to harnessing quantum mechanics for everyday applications. Every day, researchers continue to push the boundaries of our collective understanding. This means we may soon see the emergence of technologies that revolutionize the way we interact with this mysterious and wonderful world around us.