As the story goes, the Greek mathematician and thinker Archimedes came across an invention while traveling through ancient Egypt, which would later bear his name. It was a machine consisting of a screw contained in a hollow tube that caught and drew water by rotation. Now, researchers led by Stanford University physicist Benjamin Lev have developed a quantum version of Archimedes̵
“My expectation for our system was that the stability of the gas would change only slightly,” said Lev, an associate professor of applied physics and physics at the School of Humanities and Sciences at Stanford. “I did not expect to see a dramatic, complete stabilization of it. It was beyond my wildest perception.”
Along the way, the researchers also observed the development of species – extremely rare trajectories of particles in an otherwise chaotic quantum system, where the particles repeatedly trace their steps as traces that overlap in the forest. Species states are of particular interest because they can provide a protected refuge for information encoded in a quantum system. The existence of art states in a quantum system with many interacting particles – known as a quantum body system – has only recently been confirmed. The Stanford experiment is the first example of scar status in a quantum gas with many bodies and only the second ever observation of the phenomenon.
Super and stable
Lev specializes in experiments that expand our understanding of how different parts of a quantum system with many bodies settle at the same temperature or thermal equilibrium. This is an exciting area of exploration, because resistance to this so-called “thermalization” is the key to creating stable quantum systems that can drive new technologies, such as quantum computers.
In this experiment, the team investigated what would happen if they adjusted a very unusual experimental system with many bodies, called a super Tonks-Girardeau gas. These are highly excited one-dimensional quantum gases – atoms in a gaseous state limited to a single line of motion – tuned in such a way that their atoms develop extremely strong forces of attraction towards each other. What’s super about them is that even under extreme forces, they theoretically should not collapse into a spherical mass (as normal attractive gases will). However, in practice they collapse due to experimental shortcomings. Lev, who has a penchant for the highly 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 orientation ‘just so’. Maybe they would withstand collapse just 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 our expectation was that not much would change. We thought it would still collapse, just not that easy. ” said Lev, who is also a member of the Stanford Ginzton Lab and Q-FARM. “Wow, we were wrong.”
Their dysprosium variation ended up producing a super Tonks-Girardeau gas that remained stable no matter what. The scientists turned the atomic gas between the attractive and repulsive conditions and raised or “screwed” the system to higher and higher energy states, but the atoms still did not collapse.
Building from the foundation
Although there are no immediate practical applications of their discovery, the Lev Laboratory and their colleagues are developing the science necessary to drive the quantum technological revolution that many predict is coming. For now, Lev said, the physics of quantum-many-body systems out of equilibrium remain consistently surprising.
“There is still no textbook on the shelf that you can pull off to tell you how to build your own quantum factory,” he said. “If you compare quantum science with where we were when we discovered what we needed to know to build chemical plants, it says it’s like we’re doing late 19th century work right now.”
These researchers have only begun to examine the many questions they have about their quantum Archimedes’ screw, including how to mathematically describe these art states, and whether the system is thermalizing – which it ultimately has to – how to do it. More immediately, they plan to measure the atoms in the scar states to begin developing a solid theory of why their system behaves the way it does.
The results of this experiment were so unexpected that Lev says he can not strongly predict what new knowledge will come from deeper inspection of Quantum Archimedes’ screw. But that, he points out, is perhaps experimentalism at its best.
“This is one of the few times in my life where I have actually worked on an experiment that was really experimental and not a demonstration of existing theory. I did not know what the answer would be in advance,” Lev said. “Then we found something that was really new and unexpected, and that made me say ‘Yay experimental!’
Recording of quantum measurement for the first time
“Topological pumping of a 1D dipolar gas in highly correlated prethermal states” Science (2021). science.sciencemag.org/cgi/doi… 1126 / science.abb4928
Provided by Stanford University
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