Caltech-led team confirms quantum theory predictions for the first time

An international team of physicists has used a quantum simulator to directly observe energy spectra predicted by conformal field theory for the first time, confirming decades-old theoretical predictions about how quantum systems behave at critical points between order and disorder. The findings, published in Nature on August 19, were led by Caltech's Manuel Endres and Jason Alicea in collaboration with researchers in Paris and Munich.techexplorist+1

Measuring the Quantum Ladder

Conformal field theories describe universal behaviors that emerge when quantum systems sit at the boundary between ordered and disordered states. While these theories are foundational in modern physics — spanning high-energy particle physics and condensed matter — their core predictions had never been directly verified experimentally.techexplorist

The team arranged strontium atoms into ordered chains using optical tweezers, then excited them into Rydberg states where neighboring atoms interact strongly. By carefully tuning laser parameters, they pushed the atomic chains to quantum critical points and used a newly invented technique called many-body modulation spectroscopy to measure energy levels. The method works by shaking the chain with laser pulses at varying frequencies and detecting resonant responses — much like rubbing the rim of a wine glass at the right speed to produce a clear tone.techexplorist

"We repeated the experiment on chains of up to 35 atoms, and the rungs came out as predicted by the Ising conformal field theory: the spectra collapsed onto a single universal curve once rescaled for size," said Xiangkai Sun, a co-lead author.techexplorist

Hidden Patterns and Future Directions

Because each atom can be individually controlled, the researchers uncovered a second hidden set of energy levels sorted by symmetry — something impossible to probe in ordinary materials. They also tuned to the tricritical Ising point and measured its distinct spectrum, finding energy ratios that matched theoretical predictions.caltech+1

"It's one thing to believe these theories, but another to actually poke and prod them in the lab," said Alicea. "Seeing the predictions come to life is beautiful".techexplorist

Strengthening Confidence in Quantum Simulation

The result arrives alongside a separate advance in quantum simulation reliability. Researchers at the Technical University of Munich and the University of Innsbruck, led by Tristan Kraft and Peter Zoller, published a method in Physical Review X for producing quantitative error bounds on quantum simulator results. Demonstrated on an ion-trap system with up to 51 ions, the technique learns a simulator's actual behavior from experimental data and calculates how uncertainties affect outcomes.eurekalert+1

"The quantum simulator thus provides not just a single value, but a result with error margins that quantify its accuracy," Kraft said.eurekalert

The Caltech team plans to extend its work from one-dimensional chains to two-dimensional grids. "In two dimensions, conformal field theories are much less understood, so this is an exciting opportunity," Sun noted.techexplorist