arXiv subjects

L. F. Santos

Publications and source records attributed to L. F. Santos.

29 records · Page 2Linked to original sources

arXiv2004

Entanglement versus chaos in disordered spin chains

We use a Heisenberg spin-1/2 chain to investigate how chaos and localization may affect the entanglement of pairs of qubits. To measure how much entangled a pair is, we compute its concurrence, which is then analyzed in the delocalized/localized and in the chaotic/non-chaotic regimes. Our results indicate that chaos reduces entanglement and that entanglement decreases in the region of strong localization. In the transition region from a chaotic to a non-chaotic regime localization increases entanglement. We also show that entanglement is larger for strongly interacting qubits (nearest neighbors) than for weakly interacting qubits (next and next-next neighbors).

quant-ph↗

arXiv2003

Antiresonance and interaction-induced localization in spin and qubit chains with defects

We study a spin chain with an anisotropic XXZ coupling in an external field. Such a chain models several proposed types of a quantum computer. The chain contains a defect with a different on-site energy. The interaction between excitations is shown to lead to two-excitation states localized next to the defect. In a resonant situation scattering of excitations on each other might cause decay of an excitation localized on the defect. We find that destructive quantum interference suppresses this decay. Numerical results confirm the analytical predictions.

cond-mat↗

arXiv2003

Two-particle localization and antiresonance in disordered spin and qubit chains

We show that, in a system with defects, two-particle states may experience destructive quantum interference, or antiresonance. It prevents an excitation localized on a defect from decaying even where the decay is allowed by energy conservation. The system studied is a qubit chain or an equivalent spin chain with an anisotropic ($XXZ$) exchange coupling in a magnetic field. The chain has a defect with an excess on-site energy. It corresponds to a qubit with the level spacing different from other qubits. We show that, because of the interaction between excitations, a single defect may lead to multiple localized states. The energy spectra and localization lengths are found for two-excitation states. The localization of excitations facilitates the operation of a quantum computer. Analytical results for strongly anisotropic coupling are confirmed by numerical studies.

quant-ph↗

arXiv2003

Entanglement in quantum computers described by the XXZ model with defects

We investigate how to generate maximally entangled states in systems characterized by the Hamiltonian of the XXZ model with defects. Some proposed quantum computers are described by such model. We show how the defects can be used to obtain EPR states and W states when one or two excitations are considered.

quant-ph↗

arXiv2002

Ground State Properties of Many-Body Systems in the Two-Body Random Ensemble and Random Matrix Theory

We explore generic ground-state and low-energy statistical properties of many-body bosonic and fermionic one- and two-body random ensembles (TBRE) in the dense limit, and contrast them with Random Matrix Theory (RMT). Weak differences in distribution tails can be attributed to the regularity or chaoticity of the corresponding Hamiltonians rather than the particle statistics. We finally show the universality of the distribution of the angular momentum gap between the lowest energy levels in consecutive J-sectors for the four models considered.

nucl-th↗

arXiv2001

Quantum open systems and turbulence

We show that the problem of non conservation of energy found in the spontaneous localization model developed by Ghirardi, Rimini and Weber is very similar to the inconsistency between the stochastic models for turbulence and the Navier-Stokes equation. This sort of analogy may be useful in the development of both areas.

quant-ph↗

arXiv1999

Burgers Turbulence and the Continuous Spontaneous Localization Model

There is a striking convergence between Burgers turbulence and the continuous spontaneous localization [CSL] model of quantum mechanics. In this paper, we exploit this analogy showing the similarities in the physics of these two apparently unrelated problems. It is hoped that the kind of analogy we introduce here may lead to important developments in both areas.

quant-ph↗

arXiv1999

Convergences in the Measurement Problem in Quantum Mechanics

This paper presents arguments purporting to show that von Neumann's description of the measurement process in quantum mechanics has a modern day version in the decoherence approach. We claim that this approach and the de Broglie-Bohm theory emerges from Bohr's interpretation and are therefore obliged to deal with some obscures ideas which were antecipated, explicitly or implicitly and carefully circumvented, by Bohr.

quant-ph↗

arXiv1999

Enhanced Diffusion and the Continuous Spontaneous Localization Model

We find an analogy between turbulence and the dynamics of the continuous spontaneous localization model (CSL) of the wave function. The use of a standard white noise in the localization process gives Richardson's t^3 law for the turbulent diffusion, while the introduction of an affine noise in the CSL allows us to obtain the intermittency corrections to this law.

quant-ph↗

arXiv1999

A Beable Interpretation of the Continuous Spontaneous Localization Model

We extend the beable interpretation, due to Bell, to the continuous spontaneous localization model (CSL). Results obtained by Vink are generalized to the modified Schrodinger equation of Ghirardi, Pearle and Rimini (GPR), which allows a beable interpretation for position and momentum.

quant-ph↗

arXiv1998

Stochastic Motion of an Open Bosonic String

We show that the classical stochastic motion of an open bosonic string leads to the same results as the standard first quantization of this system. For this, the diffusion constant governing the process has to be proportional to α', the Regge slope parameter, which is the only constant, along with the velocity of light, needed to describe the motion of a string.

quant-ph↗