Latest Papers in Condensed Matter Physics

Statistical Mechanics

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On the Absence of Replica Symmetry Breaking for the Random Field Ising Model in the Presence of a Class of Non-Gaussian Disorders (1811.07003v2)

Jamer Roldan, Roberto Vila

2018-11-16

This work is concerned with the theory of the Random Field Ising Model in the presence of disorders with non-Gaussian distribution on the hypercubic lattice. We showed the absence of replica symmetry in any dimensions, at any temperature and field strength, almost surely.

-Logarithmic negativity (1904.10437v1)

Xin Wang, Mark M. Wilde

2019-04-23

The logarithmic negativity of a bipartite quantum state is a widely employed entanglement measure in quantum information theory, due to the fact that it is easy to compute and serves as an upper bound on distillable entanglement. More recently, the -entanglement of a bipartite state was shown to be the first entanglement measure that is both easily computable and operationally meaningful, being equal to the exact entanglement cost of a bipartite quantum state when the free operations are those that completely preserve the positivity of the partial transpose. In this paper, we provide a non-trivial link between these two entanglement measures, by showing that they are the extremes of an ordered family of -logarithmic negativity entanglement measures, each of which is identified by a parameter . In this family, the original logarithmic negativity is recovered as the smallest with , and the -entanglement is recovered as the largest with . We prove that the -logarithmic negativity satisfies the following properties: entanglement monotone, normalization, faithfulness, and subadditivity. We also prove that it is neither convex nor monogamous. Finally, we define the -logarithmic negativity of a quantum channel as a generalization of the notion for quantum states, and we show how to generalize many of the concepts to arbitrary resource theories.

Resolving phase transitions with Discontinuous Galerkin methods (1903.09503v2)

Eduardo Grossi, Nicolas Wink

2019-03-22

We demonstrate the applicability and advantages of Discontinuous Galerkin (DG) schemes in the context of the Functional Renormalization Group (FRG). We investigate the -model in the large limit. It is shown that the flow equation for the effective potential can be cast into a conservative form. We discuss results for the Riemann problem, as well as initial conditions leading to a first and second order phase transition. In particular, we unravel the mechanism underlying first order phase transitions, based on the formation of a shock in the derivative of the effective potential.

Calculation of non-universal thermodynamic quantities within self-consistent non-perturbative functional renormalization group approach (1904.10338v1)

V. I. Tokar

2019-04-23

A self-consistent renormalization scheme suitable for the calculation of non-universal quantities in -vector models with pair spin interactions of arbitrary extent has been suggested. The method has been based on the elimination of the fluctuating field components within the layers defined by the layer-cake representation of the propagator. The non-perturbative renormalization group (RG) equations has been solved in the local potential approximation. Critical temperatures of the vector spin models on cubic lattices have been calculated in excellent agreement with the best known estimates. Several critical amplitudes and the magnetisation curve of the Ising model on the simple cubic lattice calculated within the approach compared well with the values from literature sources. It has been argued that unification of the method with cluster techniques would make possible the treatment of realistic lattice models with multi-spin interactions and describe in a unified framework the phase transitions of any kind. Besides the RG equations the layer-cake technique can be used in the exact partial renormalization of the local interactions in the functional lattice Hamiltonians. This procedure reduces the strength of the interactions which in some cases can make them amenable to perturbative treatment.

Magnetization and energy dynamics in spin ladders: Evidence of diffusion in time, frequency, position, and momentum (1811.02806v2)

Jonas Richter, Fengping Jin, Lars Knipschild, Jacek Herbrych, Hans De Raedt, Kristel Michielsen, Jochen Gemmer, Robin Steinigeweg

2018-11-07

The dynamics of magnetization and energy densities are studied in the two-leg spin-1/2 ladder. Using an efficient pure-state approach based on the concept of typicality, we calculate spatio-temporal correlation functions for large systems with up to 40 lattice sites. In addition, two subsequent Fourier transforms from real to momentum space as well as from time to frequency domain yield the respective dynamic structure factors. Summarizing our main results, we unveil the existence of genuine diffusion both for spin and energy. In particular, this finding is based on four distinct signatures which can all be equally well detected: (i) Gaussian density profiles, (ii) time-independent diffusion coefficients, (iii) exponentially decaying density modes, and (iv) Lorentzian line shapes of the dynamic structure factor. The combination of (i) - (iv) provides a comprehensive picture of high-temperature dynamics in thisarchetypal nonintegrable quantum model.

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