Traditional simulated annealing utilizes thermal fluctuations for convergence in optimization problems, from circuit board design to protein folding to glassy magnets. Quantum tunneling provides a different mechanism for moving between states, with the potential for reduced time scales. We compare thermal and quantum annealing in a model Ising magnet composed of holmium dipoles in a lithium tetrafluoride matrix. The effects of quantum mechanics can be tuned in the laboratory by varying a magnetic field applied transverse to the Ising axis. This new knob permits us to:
(1) Treat quantitatively the tunneling of domain walls in a disordered ferromagnet, introducing multiple spin moves into the “computation;”
(2) Provide speedier optimization and memory erasure in glasses;
(3) Drive coherent spin oscillations and simultaneously encode information at different frequencies in a spin liquid.