A 256-qubit QPU Shows A Quantum Magnet Relaxing In Unexpected Ways

A 256-qubit quantum processor has simulated a two-dimensional quantum magnet, revealing unexpected behavior in its relaxation after a sudden change in magnetic field. The simulation, built from 256 rubidium atoms arranged in a square lattice, produced results at “late times” where three leading classical calculations failed to agree.

Researchers report the quantum approach allowed access to dynamics beyond the reach of current classical methods, offering insight into the complex evolution of quantum magnets. “The QPU results remained consistent across system sizes, giving us access to the dynamics after the classical calculations had lost control,” the team states.

Qubit QPU Simulates 2D Transverse-Field Ising Model

The simulation revealed a slow approach to thermal equilibrium, extending beyond the capabilities of three leading tensor-network calculations; these classical methods lost agreement at what researchers term “late times” in the simulation. This discrepancy emerged as the quantum processor tracked the behavior of a two-dimensional transverse-field Ising model, a system designed to isolate the competition between magnetic order and quantum fluctuations.

To physically represent the quantum magnet, the team arranged 256 rubidium atoms in a precise 16×16 square lattice. Ground and Rydberg states of these atoms encoded the two spin states essential to the transverse-field Ising model. Laser coupling created the transverse field, while interactions between Rydberg atoms established the ferromagnetic coupling.