Researchers at Caltech have successfully conducted experiments measuring energy levels in quantum systems, validating mathematical predictions that have been theoretical for approximately four decades. The work, published in Nature, represents the first direct experimental verification of energy spectra predicted by the Ising and tricritical Ising conformal field theories. These theories describe universal behavior that emerges when quantum systems reach critical points between different states, transitions driven entirely by quantum effects at temperatures near absolute zero rather than by conventional thermal changes.
The research involved a collaboration between Caltech’s experimental physics group led by Manuel Endres, theoretical physicist Jason Alicea’s research team, and collaborators from Université Paris-Saclay and the Technical University of Munich. The team employed quantum simulators—specialized systems designed to replicate specific quantum behaviors—rather than general-purpose quantum computers. Using newly developed quantum simulator technology, the researchers arranged strontium atoms in linear chains and manipulated them using optical tweezers, tightly focused lasers that trap individual atoms. They excited these atoms into highly excited energy states called Rydberg states, causing neighboring atoms to interact strongly and behave collectively.
To measure the predicted energy levels, the researchers developed a technique called many-body modulation spectroscopy. They gently disturbed the atomic chains by varying laser frequencies and measured the strength of the atomic response. By identifying peaks in this response across different frequencies, they could detect distinct energy levels analogous to rungs on a ladder. The measurements confirmed that energy levels appeared in the precise ratios predicted by conformal field theory—predictions that had never been directly experimentally verified before.
The experimental approach allowed the team to perform measurements that would be difficult with conventional materials because they could control individual atoms separately. This level of control enabled them to classify excitations by symmetry and discover hidden patterns in the energy structure. They also demonstrated the ability to manipulate energy ladders by changing conditions at the edges of the atomic chains, producing patterns that matched tricritical Ising theory predictions.
The research team plans to expand the experiments to larger quantum systems, eventually studying two-dimensional grids of atoms rather than only linear arrangements. Such expansions could allow investigation of quantum systems whose behavior cannot yet be calculated precisely, potentially addressing problems too complex for classical computing approaches.
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