arXiv subjects

Luca Tagliacozzo

Publications and source records attributed to Luca Tagliacozzo.

61 records · Page 4Linked to original sources

arXiv2012

Dipolar Molecules in Optical Lattices

We study the extended Bose--Hubbard model describing an ultracold gas of dipolar molecules in an optical lattice, taking into account all on-site and nearest-neighbor interactions, including occupation-dependent tunneling and pair tunneling terms. Using exact diagonalization and the multiscale entanglement renormalization ansatz, we show that these terms can destroy insulating phases and lead to novel quantum phases. These considerable changes of the phase diagram have to be taken into account in upcoming experiments with dipolar molecules.

cond-mat.quant-gas↗

arXiv2011

Entanglement renormalization and gauge symmetry

A lattice gauge theory is described by a redundantly large vector space that is subject to local constraints, and can be regarded as the low energy limit of an extended lattice model with a local symmetry. We propose a numerical coarse-graining scheme to produce low energy, effective descriptions of lattice models with a local symmetry, such that the local symmetry is exactly preserved during coarse-graining. Our approach results in a variational ansatz for the ground state(s) and low energy excitations of such models and, by extension, of lattice gauge theories. This ansatz incorporates the local symmetry in its structure, and exploits it to obtain a significant reduction of computational costs. We test the approach in the context of the toric code with a magnetic field, equivalent to Z2 lattice gauge theory, for lattices with up to 16 x 16 sites (16^2 x 2 = 512 spins) on a torus. We reproduce the well-known ground state phase diagram of the model, consisting of a deconfined and spin polarized phases separated by a continuous quantum phase transition, and obtain accurate estimates of energy gaps, ground state fidelities, Wilson loops, and several other quantities.

cond-mat.str-el↗

arXiv2011

Entanglement entropy of two disjoint intervals in c=1 theories

We study the scaling of the Renyi entanglement entropy of two disjoint blocks of critical lattice models described by conformal field theories with central charge c=1. We provide the analytic conformal field theory result for the second order Renyi entropy for a free boson compactified on an orbifold describing the scaling limit of the Ashkin-Teller (AT) model on the self-dual line. We have checked this prediction in cluster Monte Carlo simulations of the classical two dimensional AT model. We have also performed extensive numerical simulations of the anisotropic Heisenberg quantum spin-chain with tree-tensor network techniques that allowed to obtain the reduced density matrices of disjoint blocks of the spin-chain and to check the correctness of the predictions for Renyi and entanglement entropies from conformal field theory. In order to match these predictions, we have extrapolated the numerical results by properly taking into account the corrections induced by the finite length of the blocks to the leading scaling behavior.

cond-mat.stat-mech↗

arXiv2010

Entanglement entropy of two disjoint blocks in critical Ising models

We study the scaling of the Renyi and entanglement entropy of two disjoint blocks of critical Ising models, as function of their sizes and separations. We present analytic results based on conformal field theory that are quantitatively checked in numerical simulations of both the quantum spin chain and the classical two dimensional Ising model. Theoretical results match the ones obtained from numerical simulations only after taking properly into account the corrections induced by the finite length of the blocks to their leading scaling behavior.

cond-mat.stat-mech↗

arXiv2007

Direct numerical computation of disorder parameters

In the framework of various statistical models as well as of mechanisms for color confinement, disorder parameters can be developed which are generally expressed as ratios of partition functions and whose numerical determination is usually challenging. We develop an efficient method for their computation and apply it to the study of dual superconductivity in 4d compact U(1) gauge theory.

hep-lat↗

arXiv2006

Monopole-Antimonopole Correlation Functions in 4D U(1) Gauge Theory

We study the two-point correlator of a modified Confined-Coulomb transition order parameter in four dimensional compact U(1) lattice gauge theory with Wilson action. Its long distance behavior in the confined phase turns out to be governed by a single particle decay. The mass of this particle is computed and found to be in agreement with previous calculations of the 0^{++} gaugeball mass. Remarkably, our order parameter allows to extract a good signal to noise ratio for masses with low statistics. The results we present provide a numerical check of a theorem about the structure of the Hilbert space describing the confined phase of four dimensional compact U(1) lattice gauge theories.

hep-lat↗

arXiv2003

Compact lattice U(1) and Seiberg-Witten duality

Simulations in compact U(1) lattice gauge theory in 4D show now beyond any reasonable doubts that the phase transition separating the Coulomb from the confined phase is of first order, albeit a very weak one. This settles the issue from the numerical side. On the analytical side, it was suggested some time ago, based on the qualitative analogy between the phase diagram of such a model and the one of scalar QED obtained by soft breaking the N=2 Seiberg-Witten model down to N=0, that the phase transition should be of second order. In this work we take a fresh look at this issue and show that a proper implementation of the Seiberg-Witten model below the supersymmetry breaking scale requires considering some new radiative corrections. Through the Coleman-Weinberg mechanism this turns the second order transition into a weakly first order one, in agreement with the numerical results. We comment on several other aspects of this continuum model.

hep-th↗