The approach resembles running a wet finger around a wine glass: only the matching frequency makes the glass ring.

What did the data show?

For chains ranging from a few atoms up to 35, the measured spectrum collapsed onto a single universal curve once rescaled for system size, matching the Ising theory. At the tricritical point, the lowest levels appeared in a different set of ratios that the tricritical Ising theory predicts.

The team's atom-by-atom control also let them classify the excitations by symmetry. That step exposed a second ladder of energy levels hidden in the initial measurement. They then altered the behavior of the atoms at the chain's two ends and watched the ladder rearrange in patterns also consistent with the tricritical Ising theory.

Why does it matter?

"Physicists call this trait universality — the messy, microscopic details wash out and only a few essential features survive," says Jason Alicea, William K. Davis Professor of Theoretical Physics at Caltech.

"The energy levels predicted by these theories are important because they encode profound information about the theories themselves," Alicea adds.

Xiangkai Sun, a co-lead author and graduate student in Endres's lab, summed up the technique: "Our new tools borrow from quantum computing platforms. Over the past 10 years, people have been learning to control these systems, and now we are at the point where we can use them to do fundamental physics research."

Alicea says the result settles a long-standing theoretical question. "Even though we believed these theories to be true," he notes, "it's important to have an experimental realization, something you can poke and prod. To see those predictions borne out is a beautiful thing."

What's next?

The researchers want to step from one-dimensional chains into two-dimensional grids of atoms. "In two dimensions, the conformal field theories are not as well understood, so this is an exciting opportunity," Sun says.

Manuel Endres, professor of physics and leader of the experimental group, says the longer-term goal is to aim the tool at problems with no known answer. "What excites me is that the technique doesn't require knowing the answer in advance," Endres says. "Here we could check our measurements against exact predictions."

The next step, he adds, "is to point this at systems where nobody knows the response of the system quantitatively — including regimes that classical computers can't reach."

Who built it?

The Nature paper, "Observation of conformal field theory spectra in a quantum simulator," brings together Caltech's Endres and Alicea groups with theorists at Université Paris-Saclay and the Technical University of Munich. It appears in Nature volume 657, issue 8130, page 98 (DOI: 10.1038/s41586-026-10904-x).

Other Caltech authors include Yuan Le, Stephen Naus, Richard Bing-Shiun Tsai, and Lewis Picard, now at the Caltech-linked startup Oratomic. Additional authors are Sara Murciano (Université Paris-Saclay, previously a Caltech postdoc) and Michael Knap of the Technical University of Munich and the Munich Center for Quantum Science and Technology.

Funders include the U.S. Department of Energy (including its Quantum Systems Accelerator and Quantum Science Center), the National Science Foundation (including the Institute for Quantum Information and Matter at Caltech), the Army Research Office, DARPA, the Air Force Office of Scientific Research, the Gordon and Betty Moore Foundation, and the Deutsche Forschungsgemeinschaft.