This review summarizes recent developments in the theory of spin glasses, as well as pertinent experimental data. The most characteristic properties of spin glass systems are described, and related phenomena in other glassy systems (dielectric and orientational glasses) are mentioned. The Edwards-Anderson model of spin glasses and its treatment within the replica method and mean-field theory are outlined, and concepts such as "frustration," "broken replica symmetry," "broken ergodicity," etc., are discussed. The dynamic approach to describing the spin glass transition is emphasized. Monte Carlo simulations of spin glasses and the insight gained by them are described. Other topics discussed include site-disorder models, phenomenological theories for the frozen phase and its excitations, phase diagrams in which spin glass order and ferromagnetism or antiferromagnetism compete, the Ne\'el model of superparamagnetism and related approaches, and possible connections between spin glasses and other topics in the theory of disordered condensed-matter systems.

Spin glasses: Experimental facts, theoretical concepts, and open questions

The simple act of slowly varying the parameters of a quantum system so that it remains always in its ground state is extremely rich from an information processing point of view. For an ideal, closed system, this adiabatic evolution is equivalent to full quantum computation, and it is convenient for establishing quantum algorithms for optimization. This review presents adiabatic quantum algorithms, proves the closed-system equivalence of the adiabatic and circuit models of quantum computation, reviews the placement of adiabatic quantum computation in the more general classification of computational complexity theory, and discusses the case of ``stoquastic'' quantum evolutions.

Adiabatic quantum computation

We propose a generalization of the cavity method to quantum spin glasses on fixed connectivity lattices. Our work is motivated by the recent refinements of the classical technique and its potential application to quantum computational problems. We numerically solve for the phase structure of a connectivity $q=3$ transverse field Ising model on a Bethe lattice with $\ifmmode\pm\else\textpm\fi{}J$ couplings and investigate the distribution of various classical and quantum observables.

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Cavity method for quantum spin glasses on the Bethe lattice

The infinite-range Ising spin glass in the presence of a transverse field is considered. Using the generalised Trotter formula and replica methods, the free energy for the system with quenched random bond interactions is evaluated using the static approximation. It is shown that, when the strength of the transverse field equals the largest eigenvalue of the random bond interaction matrix, the spin glass transition is destroyed. The authors also show that a replica-symmetric spin glass phase is stable in a certain region of the temperature-field phase diagram. Finally they present suggestive arguments which indicate that, when the time dependence of the dynamic susceptibility is included, then the stability of the replica-symmetric phase is enhanced.

https://iopscience.iop.org/article/10.1088/0305-4470/22/16/023/pdf

Infinite-range Ising spin glass in a transverse field

In the Sherrington-Kirkpatrick model the effect of a transverse field Delta on spin glass freezing is studied. After the static approximation of the replica theory has been analysed, the nonlinear susceptibility is calculated by the perturbation method with respect to exchange coupling Jij up to the tenth order. The freezing temperature and the critical index of the nonlinear susceptibility are evaluated. The result shows that the system remains paramagnetic for Delta >1.506 J (the variance of (Jij) is J2/N), which corrects the conjecture made before by the present authors. It is also shown that the static approximation in the replica theory overestimates Tc for a large value of Delta .

https://iopscience.iop.org/article/10.1088/0022-3719/20/35/020/pdf

K.D. Usadel

Papers

Spin glass transition in an Ising spin system with transverse field