Quantum annealers show full magnetic reversal in antiferromagnets

Researchers at Los Alamos National Laboratory have observed full saturation and reversal of the hysteresis curve in antiferromagnetic models using programmable quantum annealers. This finding challenges expectations, as antiferromagnets typically resist magnetization, making complete reversal an unusual result. The team detected Barkhausen-like noise, typically associated with ferromagnetic materials, alongside emergent magnetic domains created by quantum fluctuations. These fluctuations mediate magnetic memory within the antiferromagnets, demonstrating a direct link between quantum effects and a material property. The team implemented a sampling-based magnetic hysteresis protocol on these processors to investigate magnetic memory within antiferromagnetic models, revealing unexpected results about how these materials respond to external fields. This approach allows for emulation of magnetic hysteresis experiments, offering a new avenue for studying complex magnetic phenomena. The Los Alamos team focused on Transverse-Field Ising Models, both one and two-dimensional, as baseline geometries for probing antiferromagnetic hysteresis, and also examined results from D-Wave processor lattices with more complex connectivity. These quantum annealers operate at approximately 15 millikelvin, using superconducting flux qubits connected in repeating subgraph units, and are programmed to realize time-dependent transverse field Ising models. The researchers’ protocol uses a transverse field to enable…