This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: When different materials transition from one phase to another, such as water coming to a boil or a magnet losing its ability to attract metals, something remarkable can happen: They begin to behave identically, following the same mathematical rules. "Physicists call this trait universality—the messy, microscopic details wash out and only a few essential features survive," explains Jason Alicea, William K.
Davis Professor of Theoretical Physics. The math underlying these universal traits is commonly described by a theoretical framework called conformal field theory. Reporting in the journal Nature, a collaboration between the experimental group of Caltech's Manuel Endres, professor of physics, and Alicea's theory group, together with theorists at Université Paris-Saclay and the Technical University of Munich, performed first-of-their-kind experiments on two different conformal field theories using quantum simulators, which are simplified versions of quantum computers tailored for specific tasks.
Using new technology developed for these quantum simulators, the team reports the first direct measurement of energy levels in synthetic quantum matter as predicted by the Ising and tricritical Ising conformal field theories. (Ising refers to Ernst Ising, a physicist who, in the 1920s, solved an early model of magnetism.) Both theories describe universal behavior that emerges when a quantum system—exhibiting exotic traits such as entanglement and superposition—is placed at a tipping point between two states, one of which is more ordered than the other. Unlike transitions familiar from everyday life, such as water turning into steam, this one is driven not by temperature but by quantum effects alone that happen to take place at temperatures near absolute zero. Once at that tipping point, the system can be excited by lasers to reach a series of specific energies, like the rungs of a ladder.
"The energy levels predicted by these theories are important because they encode profound information about the theories themselves," Alicea says. For four decades, researchers used conformal field theories to calculate the spacings between those rungs, which come in precise ratios, but nobody had measured them in an experiment until now. "Our new tools borrow from quantum computing platforms," says Xiangkai Sun, a co-lead author of the new study and a graduate student working in the Endres lab.
"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." The quantum system in the study is based on platforms the Endres lab uses to build quantum computers: arrays of neutral atoms trapped by lasers called optical tweezers. A related neutral-atom platform in the lab recently set a milestone by trapping 6,100 atoms in a single array. Though the tweezer technology behind these arrays was developed largely with quantum computing in mind, in the new study, the team turned it toward a question in fundamental physics.
For the experiment, the researchers used optical tweezers to trap strontium atoms in a line. They used other lasers to excite the atoms into high-energy states called Rydberg states, which make neighboring atoms interact strongly. The chain of atoms then behaved as a single entity rather than as independent particles.
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