One Broken Symmetry Opens a Path to Universal Quantum Control

Insider Brief

• Researchers developed a theory of universal control in globally driven quantum systems and demonstrated an effective three-atom interaction in a Rydberg-atom experiment.
• For a one-dimensional qubit chain with uniform nearest-neighbor interactions and global rotations, adding a controllable field or interaction that breaks mirror symmetry enables universal quantum control.
• Optimized global pulses produced a three-atom ZXZ interaction in an eight-atom chain, with measurements showing signatures of topological edge modes.

PRESS RELEASE — A new theory identifies what globally driven quantum systems need to become fully controllable. In a Rydberg-atom experiment, optimized pulses also create an interaction involving three atoms at once.

The study by Hong-Ye Hu and colleagues is forthcoming in Nature Physics. The linked manuscript is the authors’ preprint.

Many quantum simulators use a small number of laser fields that act on every atom at once. This shared control can make large systems easier to operate, but it raises a basic question: can a device controlled globally perform a full range of quantum operations, or is it limited to the interactions built into its hardware?

For a one-dimensional chain of qubits, the researchers prove a precise rule. With uniform interactions between neighboring qubits and global rotations, the remaining obstacle is mirror symmetry: atoms on opposite sides of the chain are indistinguishable. Add a controllable interaction or field that breaks that symmetry, and universal quantum control becomes possible. The team also extends related results to fermionic and bosonic systems.