arXiv subjects

A. Yuste

Publications and source records attributed to A. Yuste.

4 recordsLinked to original sources

arXiv2019

Frustrated quantum spin systems in small triangular lattices studied with a numerical method

The study of quantum frustrated systems remains one of the most challenging subjects of quantum magnetism, as they can hold quantum spin liquids, whose characterization is quite elusive. The presence of gapped quantum spin liquids possessing long range entanglement while being locally indistinguishable often demand highly sophisticated numerical approaches for their description. Here we propose an easy computational method based on exact diagonalization with engineered boundary conditions in very small plaquettes. We apply the method to study the quantum phase diagram of diverse antiferromagnetic frustrated Heisenberg models in the triangular lattice. Our results are in qualitative agreement with previous results obtained by means of sophisticated methods like 2D-DMRG or variational quantum Monte Carlo.

cond-mat.str-el↗

arXiv2017

Entanglement scaling at first order phase transitions

First order quantum phase transitions (1QPTs) are signaled, in the thermodynamic limit, by discontinuous changes in the ground state properties. These discontinuities affect expectation values of observables, including spatial correlations. When a 1QPT is crossed in the vicinity of a second order one (2QPT), due to the correlation length divergence of the latter, the corresponding ground state is modified and it becomes increasingly difficult to determine the order of the transition when the size of the system is finite. Here we show that, in such situations, it is possible to apply finite size scaling to entanglement measures, as it has recently been done for the order parameters and the energy gap, in order to recover the correct thermodynamic limit. Such a finite size scaling can unambigously discriminate between first and second order phase transitions in the vicinity of multricritical points even when the singularities displayed by entanglement measures lead to controversial results.

quant-ph↗

arXiv2016

Using Random Boundary Conditions to simulate disordered quantum spin models in 2D-systems

Disordered quantum antiferromagnets in two-dimensional compounds have been a focus of interest in the last years due to their exotic properties. However, with very few exceptions, the ground states of the corresponding Hamiltonians are notoriously difficult to simulate making their characterization and detection very elusive, both, theoretically and experimentally. Here we propose a method to signal quantum disordered antiferromagnets by doing exact diagonalization in small lattices using random boundary conditions and averaging the observables of interest over the different disorder realizations. We apply our method to study a Heisenberg spin-1/2 model in an anisotropic triangular lattice. In this model, the competition between frustration and quantum fluctuations might lead to some spin liquid phases as predicted from different methods ranging from spin wave mean field theory to 2D-DMRG or PEPS. Our method accurately reproduces the ordered phases expected of the model and signals disordered phases by the presence of a large number of quasi degenerate ground states together with the absence of a local order parameter. The method presents a weak dependence on finite size effects.

cond-mat.quant-gas↗

arXiv2013

Shortcut to adiabaticity in internal bosonic Josephson junctions

We extend a recent method to shortcut the adiabatic following to internal bosonic Josephson junctions in which the control parameter is the linear coupling between the modes. The approach is based on the mapping between the two-site Bose-Hubbard Hamiltonian and a 1D effective Schrödinger-like equation, valid in the large $N$ (number of particles) limit. Our method can be readily implemented in current internal bosonic Josephson junctions and it improves substantially the production of spin-squeezing with respect to usually employed linear rampings.

cond-mat.quant-gas↗