Latest Research Papers In Condensed Matter Physics | (Cond-Mat.Stat-Mech) 2019-03-16

Latest Papers in Condensed Matter Physics

Statistical Mechanics


Quantum many-body dynamics on the star graph (1903.01468v2)

Andrew Lucas

2019-03-04

We study 2-local Hamiltonian quantum systems, consisting of qubits interacting on the star graph of N vertices. We numerically demonstrate that these models are generically non-integrable at infinite temperature, and find evidence for a finite temperature phase transition to a glassy phase in generic models. Operators can become complicated in constant time: we explicitly find that there is no bound on out-of-time-ordered correlators, even at finite temperature. Operator growth is not correctly modeled by stochastic quantum dynamics, including Brownian Hamiltonian dynamics or random unitary circuits. The star graph (and similar constructions) may serve as a useful testing ground for conjectures about universality, quantum chaos and Planckian dissipation in k-local systems, including in experimental quantum simulators.

Range separation: The divide between local structures and field theories (1902.03289v2)

David M. Rogers

2019-02-08

This work presents parallel histories of the development of two modern theories of condensed matter: the theory of electron structure in quantum mechanics, and the theory of liquid structure in statistical mechanics. Comparison shows that key revelations in both are not only remarkably similar, but even follow along a common thread of controversy that marks progress from antiquity through to the present. This theme appears as a creative tension between two competing philosophies, that of short range structure (atomistic models) on the one hand, and long range structure (continuum or density functional models) on the other. The timeline and technical content are designed to build up a set of key relations as guideposts for using density functional theories together with atomistic simulation.

Universal behavior in finite 2D kinetic ferromagnets (1809.09523v2)

James Denholm, Ben Hourahine

2018-09-25

We study the time evolution of the two-dimensional kinetic Ising model in finite systems with a non-conserved order parameter, considering nearest-neighbour interactions on the square lattice with periodic and open boundary conditions. Universal data collapse in spin product correlation functions is observed which, when expressed in rescaled units, is valid across the entire time evolution of the system at all length scales, not just within the time regime usually considered in the dynamical scaling hypothesis. Consequently, beyond rapidly decaying finite size effects, the evolution of correlations in small finite systems parallels arbitrarily larger cases, even at large fractions of the size of these finite systems.

Renormalization of multicritical scalar models in curved space (1810.06395v3)

Riccardo Martini, Omar Zanusso

2018-10-15

We consider the leading order perturbative renormalization of the multicritical models and some generalizations in curved space. We pay particular attention to the nonminimal interaction with the scalar curvature and discuss the emergence of the conformal value of the coupling as the renormalization group fixed point of its beta function at and below the upper critical dimension as a function of . We also examine our results in relation with Kawai and Ninomiya's formulation of two dimensional gravity.

Direct evaluation of dynamical large-deviation rate functions using a variational ansatz (1903.06098v1)

Daniel Jacobson, Stephen Whitelam

2019-03-14

We describe a simple way to bound and compute large-deviation rate functions for time-extensive dynamical observables in continuous-time Markov chains. We start with a model, defined by a set of rates, and a time-extensive dynamical observable. We construct a reference model, a variational ansatz for the behavior of the original model conditioned on atypical values of the observable. Direct simulation of the reference model provides an upper bound on the large-deviation rate function associated with the original model, an estimate of the tightness of the bound, and, if the ansatz is chosen well, the exact rate function. The exact rare behavior of the original model does not need to be known in advance. We use this method to calculate rate functions for currents and counting observables in a set of network- and lattice models taken from the literature. Straightforward ansatze yield bounds that are tighter than bounds obtained from Level 2.5 of large deviations via approximations that homogenize connections between states. In all cases we can correct these bounds to recover the rate functions exactly. Our approach is complementary to more specialized methods, and offers a physically transparent framework for approximating and calculating the likelihood of dynamical large deviations.



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