University of Chicago

Title: Attacking Optimization Problems with Quantum Mechanics

Abstract: Traditional simulated annealing utilizes thermal fluctuations for convergence in optimization problems. 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 ferromagnet 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) tune the crossover between a classical Arrhenius response at high temperatures and an athermal response below 100 mK;
(2) quantify the tunneling of magnetic domain walls through the potential barriers in the free energy surface. We find that spins tunnel coherently on the nanometer scale; and
(3) hasten convergence to the optimal state.