Abstract:We investigate the properties of quantum annealing applied to the random field Ising model in one, two and three dimensions. The decay rate of the residual energy, defined as the energy excess from the ground state, is find to be eres ∼ log(NMC ) −ζ with ζ in the range 2...6, depending on the strength of the random field. Systems with "large clusters" are harder to optimize as measured by ζ. Our numerical results suggest that in the ordered phase ζ = 2 whereas in the paramagnetic phase the annealing procedure … Show more
“…We show that the power decay (21) satisfies the adiabaticity condition (17) which guarantees convergence to the ground state of H Ising as t → ∞. .…”
Section: Transverse Field Ising Modelmentioning
confidence: 88%
“…Here a and c are constants of O(N 0 ) and δ is a small parameter to control adiabaticity appearing in (17).…”
Section: Transverse Field Ising Modelmentioning
confidence: 99%
“…We shall show some theoretical bases for these conclusions in this paper. Numerical evidence is found in [9,10,11,14,15,16,17,18,19,20,21,22].…”
Quantum annealing is a generic name of quantum algorithms to use quantum-mechanical fluctuations to search for the solution of optimization problem. It shares the basic idea with quantum adiabatic evolution studied actively in quantum computation. The present paper reviews the mathematical and theoretical foundation of quantum annealing. In particular, theorems are presented for convergence conditions of quantum annealing to the target optimal state after an infinite-time evolution following the Schrödinger or stochastic (Monte Carlo) dynamics. It is proved that the same asymptotic behavior of the control parameter guarantees convergence both for the Schrödinger dynamics and the stochastic dynamics in spite of the essential difference of these two types of dynamics. Also described are the prescriptions to reduce errors in the final approximate solution obtained after a long but finite dynamical evolution of quantum annealing. It is shown there that we can reduce errors significantly by an ingenious choice of annealing schedule (time dependence of the control parameter) without compromising computational complexity qualitatively. A review is given on the derivation of the convergence condition for classical simulated annealing from the view point of quantum adiabaticity using a classical-quantum mapping.
“…We show that the power decay (21) satisfies the adiabaticity condition (17) which guarantees convergence to the ground state of H Ising as t → ∞. .…”
Section: Transverse Field Ising Modelmentioning
confidence: 88%
“…Here a and c are constants of O(N 0 ) and δ is a small parameter to control adiabaticity appearing in (17).…”
Section: Transverse Field Ising Modelmentioning
confidence: 99%
“…We shall show some theoretical bases for these conclusions in this paper. Numerical evidence is found in [9,10,11,14,15,16,17,18,19,20,21,22].…”
Quantum annealing is a generic name of quantum algorithms to use quantum-mechanical fluctuations to search for the solution of optimization problem. It shares the basic idea with quantum adiabatic evolution studied actively in quantum computation. The present paper reviews the mathematical and theoretical foundation of quantum annealing. In particular, theorems are presented for convergence conditions of quantum annealing to the target optimal state after an infinite-time evolution following the Schrödinger or stochastic (Monte Carlo) dynamics. It is proved that the same asymptotic behavior of the control parameter guarantees convergence both for the Schrödinger dynamics and the stochastic dynamics in spite of the essential difference of these two types of dynamics. Also described are the prescriptions to reduce errors in the final approximate solution obtained after a long but finite dynamical evolution of quantum annealing. It is shown there that we can reduce errors significantly by an ingenious choice of annealing schedule (time dependence of the control parameter) without compromising computational complexity qualitatively. A review is given on the derivation of the convergence condition for classical simulated annealing from the view point of quantum adiabaticity using a classical-quantum mapping.
“…Introduction of transverse ferromagnetic interactions does not necessarily improve the result for the cases of disordered ground states. This observation is to be compared with the finding of Sarjala et al [13] who showed by quantum Monte Carlo simulations that quantum annealing by the conventional method is less efficient than simulated annealing when the ground state is strongly ferromagnetic. We may conclude that their consequence does not necessarily reflect intrinsic features of quantum annealing.…”
We introduce transverse ferromagnetic interactions, in addition to a simple transverse field, to quantum annealing of the random-field Ising model to accelerate convergence toward the target ground state. The conventional approach using only the transverse-field term is known to be plagued by slow convergence when the true ground state has strong ferromagnetic characteristics for the random-field Ising model. The transverse ferromagnetic interactions are shown to improve the performance significantly in such cases. This conclusion is drawn from the analyses of the energy eigenvalues of instantaneous stationary states as well as by the very fast algorithm of Bethe-type mean-field annealing adopted to quantum systems. The present study highlights the importance of a flexible choice of the type of quantum fluctuations to achieve the best possible performance in quantum annealing. The existence of such flexibility is an outstanding advantage of quantum annealing over simulated annealing.
“…The logarithmic scaling was recently supported by the quantum Monte-Carlo simulation [7], though the evolution of state in quantum Monte-Carlo is different from the one ruled by the Schrödinger equation. In contrast, the authors of this paper have shown another scaling law of residual energy given by…”
Quantum annealing is a quantum algorithm proposed recently for combinatorial optimization problems. It manipulates time evolution of a quantum mechanical state and obtain an approximate solution. In order to implement the algorithm in classical computers, we propose to apply the density matrix renormalization group method. Simulation of the time evolution of a quantum mechanical state becomes possible by the density matrix renormalization group method for problems of large size. We explain quantum annealing and the density matrix renormalization group method, and present results of numerical simulation using them.
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