Quantum Simulators Confirm 40-Year-Old Predictions From Conformal Field Theory

Physicists have used quantum simulators to directly test, for the first time, decades-old predictions from conformal field theory, a mathematical framework that describes 'universal' behaviour appearing near phase transitions, such as water nearing a boil or a magnet losing its magnetism. The work was published in the journal Nature.

Caltech's experimental group, led by professor Manuel Endres, and its theory group, led by professor Jason Alicea, joined researchers at Université Paris-Saclay and the Technical University of Munich to directly measure, for the first time, energy levels predicted by the Ising and tricritical Ising conformal field theories.

To build their quantum system, the researchers arranged strontium atoms in a line using laser beams called optical tweezers, technology also used in quantum computers. Additional lasers pushed the atoms into high-energy Rydberg states, causing neighbouring atoms to interact strongly and the whole chain to behave collectively. The team adjusted the lasers until the system reached the critical point predicted by theory, then measured its energy levels using a technique called many-body modulation spectroscopy.

In chains of up to 35 atoms, the measured energy levels — once rescaled for size — matched the Ising conformal field theory's predictions. Tuning to a second, 'tricritical' point produced a different pattern of energy levels that matched the tricritical Ising theory's predictions. Sorting the results by symmetry also revealed a second family of energy levels that had been hidden in the initial measurement.

The researchers next plan to extend the technique from one-dimensional chains of atoms to two-dimensional grids, where conformal field theories are not as well understood.