Caltech physicists finally measure a quantum energy ladder predicted 40 years ago

The work joined Caltech’s experimental team led by Manuel Endres, theorist Jason Alicea’s group, and researchers from Université Paris-Saclay and the Technical University of Munich. They used quantum simulators designed to reproduce specific quantum behaviors.

The theories describe universal patterns that can emerge at critical points between states with different degrees of order. Unlike familiar changes such as water boiling, these transitions arise from quantum effects near absolute zero.

At such a critical point, laser pulses can move the system into distinct energy states. Their spacing forms a kind of energy ladder, and the relative gaps carry information about the underlying theories.

Physicists had calculated the expected ratios between these energy levels for roughly four decades, but had not measured them directly. The new simulator technology makes such fundamental tests possible; the researchers say the approach builds on a decade of progress in controlling quantum systems.