New state of matter in one-dimensional quantum gas

Throughout history, the Greek mathematician and handyman Archimedes stumbled upon an invention while traveling through ancient Egypt that would later bear his name. It was a machine made up of a screw housed inside a hollow tube that trapped and sucked water during rotation. Now, researchers led by Stanford University physicist Benjamin Lev have developed a quantum version of the Archimedes’ screw that, instead of water, transports fragile collections of gas atoms to states higher and higher energy without collapsing. Their discovery is detailed in an article published on January 14 in Science.

“My expectation for our system was that the stability of the gas would change only slightly,” said Lev, who is an associate professor of applied physics and physics at the School of Humanities and Sciences at Stanford. “I didn’t expect to see a dramatic and complete stabilization of this one. It was beyond my wildest conception.”

Along the way, the researchers also observed the development of scar states – extremely rare trajectories of particles in an otherwise chaotic quantum system in which particles repeatedly retrace their steps like overlapping tracks in the woods. Scar states are of particular interest because they can provide a safe haven for information encoded in a quantum system. The existence of scar states in a quantum system with many interacting particles – known as the multibody quantum system – has only recently been confirmed. The Stanford experiment is the first example of the scar condition in a multibody quantum gas and only the second observation of the phenomenon in the real world.

Super and stable

Lev specializes in experiments that expand our understanding of how different parts of a multi-body quantum system settle into the same temperature or thermal equilibrium. This is an exciting field of study because resistance to this so-called “thermalization” is essential to create stable quantum systems that could power new technologies, such as quantum computers.

In this experiment, the team explored what would happen if they modified a very unusual multi-body experimental system called the Tonks-Girardeau super gas. They are highly excited one-dimensional quantum gases – gaseous atoms confined to a single line of motion – that have been tuned in such a way that their atoms develop extremely strong attractive forces with respect to each other. What’s great about them is that, even under extreme forces, they theoretically shouldn’t collapse into a ball-shaped mass (as normal attractant gases will). However, in practice, they collapse due to experimental imperfections. Lev, who has a penchant for the strongly magnetic element dysprosium, wondered what would happen if he and his students created a super Tonks-Girardeau gas with dysprosium atoms and changed their magnetic orientations “just so”. Perhaps they would resist collapse a little better than non-magnetic gases?

“The magnetic interactions we were able to add were very weak compared to the attractive interactions already present in the gas. So we expected not much to change. We thought it would collapse again, but not so easily. . ” said Lev, who is also a member of the Stanford Ginzton Lab and Q-FARM. “Wow, we were wrong.”

Their variation of dysprosium ended up producing a super Tonks-Girardeau gas that remained stable no matter what. The researchers switched atomic gas between attractive and repulsive conditions, raising or “screwing” the system to higher and higher energy states, but the atoms still did not collapse.

Building from the foundation

While there are no immediate practical applications for their discovery, Lev’s lab and their colleagues are developing the science necessary to fuel this quantum technological revolution that many predict. For now, says Lev, the physics of out-of-equilibrium multi-body quantum systems is still surprising.

“There isn’t a manual on the shelf yet that you can pull out to tell you how to build your own quantum factory,” he said. “If you compare quantum science to where we were when we found out what we needed to know to build chemical factories, say, it’s like we’re doing the work of the late 19th century right now. .

These researchers are only beginning to examine the many questions they have about the quantum Archimedes screw, including how to mathematically describe these scar states and whether the system is thermalizing – which it eventually needs to – how it s ‘takes it. More immediately, they plan to measure the momentum of atoms in scar states to begin to develop a solid theory about why their system behaves the way it does.

The results of this experiment were so unexpected that Lev says he can’t predict with certainty what new knowledge will come from a closer inspection of the Archimedes quantum screw. But that, he points out, is perhaps the best of experimentation.

“This is one of the few times in my life that I have worked on an experiment that was really experimental and not a demonstration of existing theory. I didn’t know what the answer would be in advance,” said Lev. “Then we found something really new and unexpected that made me say, ‘Yay experimentalists! “”