TY - JOUR

T1 - Geometric approach to optimal nonequilibrium control

T2 - Minimizing dissipation in nanomagnetic spin systems

AU - Rotskoff, Grant M.

AU - Crooks, Gavin E.

AU - Vanden-Eijnden, Eric

N1 - Funding Information:
G.M.R. gratefully acknowledges support from the NSF graduate research fellowship. G.E.C. was supported in part by the U.S. Army Research Laboratory and the U.S. Army Research Office under Contract No. W911NF-13-1-0390. E.V.E. was supported in part by NSF Grant No. DMS-1522767
Publisher Copyright:
© 2017 American Physical Society.

PY - 2017/1/25

Y1 - 2017/1/25

N2 - Optimal control of nanomagnets has become an urgent problem for the field of spintronics as technological tools approach thermodynamically determined limits of efficiency. In complex, fluctuating systems, such as nanomagnetic bits, finding optimal protocols is challenging, requiring detailed information about the dynamical fluctuations of the controlled system. We provide a physically transparent derivation of a metric tensor for which the length of a protocol is proportional to its dissipation. This perspective simplifies nonequilibrium optimization problems by recasting them in a geometric language. We then describe a numerical method, an instance of geometric minimum action methods, that enables computation of geodesics even when the number of control parameters is large. We apply these methods to two models of nanomagnetic bits: a Landau-Lifshitz-Gilbert description of a single magnetic spin controlled by two orthogonal magnetic fields, and a two-dimensional Ising model in which the field is spatially controlled. These calculations reveal nontrivial protocols for bit erasure and reversal, providing important, experimentally testable predictions for ultra-low-power computing.

AB - Optimal control of nanomagnets has become an urgent problem for the field of spintronics as technological tools approach thermodynamically determined limits of efficiency. In complex, fluctuating systems, such as nanomagnetic bits, finding optimal protocols is challenging, requiring detailed information about the dynamical fluctuations of the controlled system. We provide a physically transparent derivation of a metric tensor for which the length of a protocol is proportional to its dissipation. This perspective simplifies nonequilibrium optimization problems by recasting them in a geometric language. We then describe a numerical method, an instance of geometric minimum action methods, that enables computation of geodesics even when the number of control parameters is large. We apply these methods to two models of nanomagnetic bits: a Landau-Lifshitz-Gilbert description of a single magnetic spin controlled by two orthogonal magnetic fields, and a two-dimensional Ising model in which the field is spatially controlled. These calculations reveal nontrivial protocols for bit erasure and reversal, providing important, experimentally testable predictions for ultra-low-power computing.

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U2 - 10.1103/PhysRevE.95.012148

DO - 10.1103/PhysRevE.95.012148

M3 - Article

C2 - 28208424

AN - SCOPUS:85012075615

VL - 95

JO - Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics

JF - Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics

SN - 1063-651X

IS - 1

M1 - 012148

ER -