“We have transformed light into a solid. It is fantastic.” The words of Dimitris Trypogeorgos they are the synthesis of an extraordinary experiment just posted on Nature. A supersolid of light. A quantum material that defies all known categories, behaving simultaneously as a solid crystal and a viscous fluid. Until yesterday, we could only imagine such exotic states of matter using ultracold atoms.
Today, thanks to a team of physicists from National Research Council Italian, the light itself has been transformed into this paradoxical state, opening the doors to a new chapter in the fundamental physics and, perhaps, to technologies that we can't even imagine yet.
When the impossible becomes experimental
It's not the first time that light surprises us. Since 2009, when Daniele Sanvitto, also a researcher at the CNR, demonstrated that light could behave like a fluid, we knew that this apparently simple element hid extraordinary properties. But taking the next step, transforming light into a supersolid, seemed an undertaking bordering on the impossible.
Yet, through a complex experimental setup combining lasers and gallium arsenide semiconductors and aluminum, the Italian researchers have succeeded. They have not only manipulated light, they've basically transformed it into something that defies any classical categorization. I wonder how many more surprises this beam of photons that we take for granted every day will have in store for us.
We are truly at the beginning of something new.
What is a supersolid and why should we be excited?
What exactly is a supersolid? Imagine taking an ice cube that, while perfectly maintaining its cubic shape, can also pass through a sieve effortlessly, as if it were water. It seems absurd, yet that is exactly what happens in these exotic states of matter: Rigid crystalline structure and frictionless flow coexist in the same material.
Until now, physicists had only been able to create supersolids by cooling atoms to temperatures very close to absolute zero (-273,15 degrees Celsius), where quantum effects dominate. The big news is that we can now obtain them by manipulating light at much higher temperatures, thanks to the interaction with specially structured semiconductor materials. This means that these quantum phenomena can be studied in much more accessible conditions.
The Italian method to tame the light
The experiment was not at all simple. The researchers had to design with micrometric precision “ridges” on the semiconductor, creating a pattern that confined the hybrid particles generated by the interaction between light and matter (the so-called “polaritons“). This confinement forced the polaritons to arrange themselves in a crystalline structure while maintaining the fluidity typical of quantum systems.
Saint Vitto highlights how many challenges they had to overcome to prove that they had actually created a supersolid of light. There were no precedents, no experimental protocol to follow. They had to measure several properties simultaneously to prove that their material was truly both solid and fluid without viscosity.
A super-solid future yet to be written
Secondo Alberto Bramati of Sorbonne University, this experiment is just the first step. There are still countless measurements to be made to fully understand the properties of this supersolid of light, but the possibilities are exciting.
Trypogeorgos suggests that these photonic supersolids might be easier to manipulate than atomic ones, opening up new avenues for studying exotic states of matter that have been inaccessible to us until now. Perhaps one day this seemingly abstract research will lead to revolutionary technologies, just as it has with other quantum phenomena that today power computers, lasers, and medical devices.
We are really just at the beginning of a new chapter in physics. And, as often happens, it all starts with a beam of light.
