Measuring Quantum Universality
Physicists have successfully tested a 40-year-old framework known as conformal field theory using advanced quantum simulators. By arranging strontium atoms in precise arrays, a research team led by Caltech professor Manuel Endres and theoretical physicist Jason Alicea observed energy levels that match long-standing mathematical predictions. This experiment marks the first time these specific energy spacings have been measured in synthetic quantum matter.
Universality dictates that diverse materials begin following identical mathematical rules at the point of phase transitions. Water boiling and magnetism loss represent traditional examples of this behavior. In the quantum realm, similar transitions occur near absolute zero, driven by quantum effects rather than heat. At these critical points, the system displays distinct energy rungs similar to a ladder.
The Role of Quantum Simulators
The researchers used technology derived from quantum computing, specifically neutral atom arrays held by optical tweezers. By utilizing lasers to force strontium atoms into high-energy Rydberg states, the team created a system where atoms behaved collectively. This setup allowed for the precise observation of energy spectra previously accessible only through abstract calculation. The work appeared in the journal Nature on August 19, 2026.
To capture these measurements, the scientists developed a process called many-body modulation spectroscopy. They varied laser frequencies across the atomic chain and observed the response, a process compared to identifying resonant frequencies in a wine glass. This technique allowed the team to reconstruct the energy ladder with accuracy. They measured chains containing up to 35 atoms to confirm the Ising and tricritical Ising theories.
Future Research and Implications
Control over individual atoms provided a secondary advantage for the experiment. By sorting excitations according to symmetry, the researchers identified hidden energy levels that previous methods missed. They also modified the ends of the atomic chains to verify predictions regarding tricritical point behavior. The experimental data confirms that these theories, while long-held as accurate, function precisely as predicted in physical systems.
Moving beyond one-dimensional chains remains the next objective. The team intends to apply this spectroscopic method to two-dimensional grids. Understanding conformal field theories in two dimensions poses a greater challenge than in one dimension, offering a path to study regimes currently beyond the reach of classical computers. This development provides a new tool for exploring physics where the final response is not yet known.
The project involved collaboration between Caltech, Université Paris-Saclay, and the Technical University of Munich. Funding sources include the Department of Energy, the National Science Foundation, the Army Research Office, and the Defense Advanced Research Projects Agency. These organizations supported the investigation into the fundamental nature of quantum matter.