Researchers at MIT and Harvard have demonstrated a method for controlling qubits using global fields, achieving a three-atom interaction, specifically an effective ZXZ interaction, that extends beyond the typical two-atom limitations of Rydberg-atom arrays. The team proved that breaking mirror symmetry, where atoms on opposite sides of a qubit chain are indistinguishable, is key to unlocking universal quantum control in these globally driven systems. “Global fields can support far richer quantum dynamics than the hardware’s built-in interactions alone would suggest,” the researchers report, and they accomplished this complex control while operating outside the normally simplifying Rydberg blockade regime.
Broken Mirror Symmetry Enables Universal Qubit Control
Breaking mirror symmetry within a one-dimensional qubit chain is demonstrably key to achieving complete quantum control using globally applied fields, according to a new theoretical rule proven by Hong-Ye Hu and colleagues. The team’s work identifies indistinguishability between atoms on opposite sides of the chain as a previously unaddressed obstacle to universal control, a finding with implications for scaling quantum simulations. This theoretical insight goes beyond simply identifying a limitation; it pinpoints a specific condition that, when addressed, allows for full operational capability.
The researchers translated this theoretical understanding into a practical method using a Rydberg-atom array, successfully creating an effective ZXZ interaction, a coupling shared by three neighboring atoms, through optimized global pulses. This three-atom interaction surpasses the device’s native pair interactions, demonstrating a capability not previously achievable with this type of system.
The experiment was conducted outside the typical Rydberg blockade regime, a surprising result given that operating beyond this regime is generally considered more difficult for maintaining control. “Universal Dynamics with Globally Controlled Analog Quantum Simulators” details the team’s findings, soon to be published in Nature Physics.
Measurements taken on a chain of eight atoms revealed distinctive signals and correlations persisting at the chain’s ends as the system evolved, a clear signature of topological edge modes. Numerical results in the paper also suggest that random global pulses can spread quantum information quickly, with characteristic measurement statistics emerging on a timescale that grows only logarithmically with the number of atoms.
See today’s quantum computing news on Quantum Zeitgeist for the latest breakthroughs in qubits, hardware, algorithms, and industry deals.
