Theoretical Physicist Wins APS Valley Prize for Work on Many-Body Quantum Physics
Ruben Verresen’s pioneering work may someday advance quantum computing.
When 12-year-old Ruben Verresen found his older brother’s physics textbook and started reading it, he was miffed. The book held clues to the secrets of the universe, and no one had thought to tell him?
Now an assistant professor of molecular engineering at the University of Chicago, Verresen is the winner of the APS George E. Valley Jr. Prize, which recognizes early-career scientists who have made outstanding contributions to physics that are likely to impact the field dramatically. Verresen received the prize for his pioneering work on many-body quantum physics.
When Verresen, who is originally from Belgium, began a theoretical physics master’s program at the Perimeter Institute in Canada, he was enthusiastic about exploring the wide range of topics — except for quantum-body physics, which didn’t seem as interesting. But when the program exposed him to the field’s frontiers, he did an about-face. “That’s where the most exciting stuff is,” he says now.
Part of what he finds so fascinating is the richness that can emerge from basic principles. Consider chess, Verresen says. Knowing the rules can give you a sense of the game, but not all the strategies and gameplay those rules can yield. Similarly, knowing the fundamental laws of nature can give you a sense of how the universe operates, but not all the behaviors, properties, and laws that can emerge from them.
Daily life is full of emergent structures. Water is one example, he says. At the molecular level, it’s composed of many H2O molecules bouncing around, “but as you zoom out, there's this effective notion of a wave.” Waves have measurable sizes and speeds, they can travel and interfere, and there are equations that describe their behavior, he says. “Where did these laws come from?”
Verresen explores collective behaviors that could emerge in systems where “the weirdest theory we have” applies — quantum physics. Over the last 100 years, scientists have discovered rich emergent structures in these systems, he says, first by exposing solid-state systems to ultracold temperatures and, more recently, with well-controlled quantum platforms. The platforms enable experimentalists to precisely arrange many atoms and fine-tune the parameters to encourage specific collective behaviors. They’re becoming increasingly capable.
Scientists can probe and measure systems in ways never before possible, says Verresen. For theorists like him, the platforms are playgrounds. Experimentalists can figure out what’s possible, and theorists can dream up ideas to explore. Then, the two groups can collaborate on experiments, with the results fueling new explorations.
Quantum computing is a strong motivation for these types of projects. “To build a quantum computer, you're going to need an immense amount of control, and you're going to need a lot of qubits,” Verresen says. “It's very naturally in unison with studying many-body quantum physics.”
Theorists have predicted that under the right conditions, certain states will emerge in materials or systems that are especially valuable for quantum computing applications. In the past, experimentalists have struggled to realize and stabilize many of these states, but technology is catching up. And thanks to Verresen and his colleagues, there’s a versatile tool at their disposal: measurement.
People usually think of measurement as a passive way to gather information, says Verresen, “but in quantum physics, measurement is a very active process.” As a postdoc at Harvard University and then at both Harvard and MIT, Verresen collaborated closely with Ashvin Vishwanath and Caltech’s Nathanan Tantivasadakarn in theorizing how experimentalists could use the act of measurement to chisel away at one quantum state in order to sculpt another desired state.
For example, Verresen says, “If I measure every other atom, can the [wavefunction of the] remaining atoms collapse so that we get a new emergent structure arising from it?”
The chiseling approach worked. In early 2024, the trio and collaborators from the quantum computing company Quantinuum published the results of an experimental study in Nature. On the company’s newest quantum platform, the team utilized measurement to realize an elusive and sought-after quantum state known as a non-Abelian topological phase. The state potentially holds promise for computing because it produces quasiparticles that can store information.
Verresen isn’t focused on quantum computing, although he says it’s a bonus that his work on quantum processors may contribute to advances in the field. “My primary interest in this topic is the beauty of these emergent structures and what it can teach us about fundamental aspects of many-body quantum states,” he says.
He’s also intrigued by the origin of emerging phenomena and their relationship to the fundamental laws of the universe. Some emergent notions seem universal but aren’t “fundamental” in the traditional sense of the word, Verresen says. If you have a quantum system “that interacts a bit, and you zoom out and all these structures can emerge, it does really invite the notion of, How much do we need to presume as fundamental?”
In August, Verresen started his role at the University of Chicago, where he’s busy setting up a group to explore an assortment of topics under the many-body quantum umbrella. When he’s not consumed with academic responsibilities, he lets his mind wander, wondering and playing with physics concepts. There are still secrets to uncover.