Theorists have speculated that the onset of chaos will greatly increase the degree to which different parts of a quantum system become entangled.

The quantum version of the top is the “spin” of individual laser-cooled cesium atoms that Jessen’s team manipulate with magnetic fields and laser light, using tools and techniques developed over a decade of painstaking laboratory work.

“Think of an atom as a microscopic top that spins on its axis at a constant rate of speed,” Jessen said. He and his students repeatedly changed the direction of the axis of spin, in a series of cycles that each consisted of a “kick” and a “twist”.

Because spinning atoms are tiny magnets, the “kicks” were delivered by a pulsed magnetic field. The “twists” were more challenging, and were achieved by subjecting the atom to an optical-frequency electric field in a precisely tuned laser beam.

They imaged the quantum mechanical state of the atomic spin at the end of each kick-and-twist cycle with a tomographic technique that is conceptually similar to the methods used in medical ultrasound and CAT scans.