Semiclassical evolution of dissipative Markovian systems

A semiclassical approximation for an evolving density operator, driven by a `closed` Hamiltonian operator and `open` Markovian Lindblad operators, is obtained. The theory is based on the chord function, i.e. the Fourier transform of the Wigner function. It reduces to an exact solution of the Lindblad master equation if the Hamiltonian operator is a quadratic function and the Lindblad operators are linear functions of positions and momenta. Initially, the semiclassical formulae for the case of Hermitian Lindblad operators are reinterpreted in terms of a (real) double phase space, generated by an appropriate classical double Hamiltonian. An extra `open` term is added to the double Hamiltonian by the non-Hermitian part of the Lindblad operators in the general case of dissipative Markovian evolution. The particular case of generic Hamiltonian operators, but linear dissipative Lindblad operators, is studied in more detail. A Liouville-type equivariance still holds for the corresponding classical evolution in double phase space, but the centre subspace, which supports the Wigner function, is compressed, along with expansion of its conjugate subspace, which supports the chord function. Decoherence narrows the relevant region of double phase space to the neighbourhood of a caustic for both the Wigner function and the chord function. This difficulty is avoided by a propagator in a mixed representation, so that a further `small-chord` approximation leads to a simple generalization of the quadratic theory for evolving Wigner functions.

QUASIDISTRIBUTIONS and COHERENT STATES FOR FINITE-DIMENSIONAL QUANTUM SYSTEMS

In recent years, an approach to discrete quantum phase spaces which comprehends all the main quasiprobability distributions known has been developed. It is the research that started with the pioneering work of Galetti and Piza, where the idea of operator bases constructed of discrete Fourier transforms of unitary displacement operators was first introduced. Subsequently, the discrete coherent states were introduced, and finally, the s-parametrized distributions, that include the Wigner, Husimi, and Glauber-Sudarshan distribution functions as particular cases. In the present work, we adapt its formulation to encompass some additional discrete symmetries, achieving an elegant yet physically sound formalism.

An introduction to numerical methods in low-dimensional quantum systems

This is an introductory course to the Lanczos Method and Density Matrix Renormalization Group Algorithms (DMRG), two among the leading numerical techniques applied in studies of low-dimensional quantum models. The idea of studying the models on clusters of a finite size in order to extract their physical properties is briefly discussed. The important role played by the model symmetries is also examined. Special emphasis is given to the DMRG.

Remarks on supersymmetry of quantum systems with position-dependent effective masses

We apply the supersymmetry approach to one-dimensional quantum systems with spatially dependent mass, by including their ordering ambiguities dependence. In this way we extend the results recently reported in the literature. Furthermore, we point out a connection between these systems and others with constant masses. This is done through convenient transformations in the coordinates and wave functions.

El Open Journal Systems en la Universidade de São Paulo: la experiencia de gestión del Portal de Revistas da USP

El objeto de este poster es presentar la experiencia de manejamiento de un portal de revistas científicas de acceso abierto, en una universidad pública y que integra los editores científicos, profesores y bibliotecarios. Iniciativas de esta naturaleza tienen importancia estratégica para la consolidación y el fortalecimiento del Movimiento de Acceso Abierto en los países en desarrollo, puesto que ofrecen la oportunidad de se vivir plenamente una cultura de acceso abierto en todas las etapas de certificación del conocimiento. La experiencia de la Universidade de São Paulo, se convierte en relevante, ya que promueve la integración de los diversos actores involucrados en la producción de revistas científicas. El Portal de Revistas da USP (http://www.revistas.usp.br), lanzado en 2008, es una iniciativa del Departamento Técnico do Sistema Integrado de Bibliotecas de USP que tiene el Programa de Apoio às Publicações Científicas Periódicas da USP. Esta iniciativa, basada en los principios del Movimiento de Acceso Abierto, tiene como objetivo promover la visibilidad y la accesibilidad de las revistas científicas publicadas oficialmente por la USP. Considerase que las revistas cumplen con un doble papel, como objeto y también vehículo de comunicación. Con esto las inversiones para calificación de las revistas incluyen recursos informáticos para garantizar la interoperabilidad entre distintos sistemas de información (bases de datos, catálogos, repositorios etc.), sistemas de gestión editorial en línea (para agilizar la tramitación de los manuscritos y la disminución de la publicación); la formación de los equipos (técnicos y bibliotecarios), atribuición de nomes DOI (digital object identifier), software de verificación de plágio. En 2012 se cambió el software de gestión del Portal para Open Journal Systems - OJS por lo cual se reunió por la primera vez, en um mismo dominio web las revistas científicas editadas en USP. De las más de 100 revistas publicadas en el Portal 29 están en DOAJ, 27 en SciELO Brasil, 20 en Scopus, 11 en JCR entre outros. En el Portal hay revistas con distintos perfiles, unas más institucionales y otras de calidad internacional. Algunas revistas más antíguas y consolidadas se utilizan de distintos sistemas de gestión de los manuscriptos y en el Portal es como un espejo para garantizar la presencia en la Universidad. Con tantas y tan distintas publicaciones el OJS se presenta como una promisora herramienta para la gestión del Portal de Revistas. El OJS surge como un sistema para la gestión individual de revistas científicos y con los avances de las tecnologías y principalmente del uso por la comunidad se conviertió en herramienta de gestión de Portal. Para una mejor gestión del Portal se presenta algunas recomendaciones, basadas en la experiencia, y que podrán mejorar el trabajo de gestión del conjunto de las revistas: en la pantalla de creación de revistas se deberá incluir todos los datos del registro oficial en ISSN, sin posibilidad de edición por los editores-gerentes; en el listado general de revistas se podría incluir una indicación de las revistas que están en línea y las que están aún en configuración; clara identificación de las revistas vigentes y no-vigentes, una vinculación mas clara de las revistas que cambiaran su título y que están vigentes; una tabla para selección de fuentes de indización; edición de contenidos ya publicados solamente por el administrador del sistema; gestión centralizada del DOI y de la preservación digital en LOCKSS y un painel con los datos estadísticos (total de revistas, ediciones, estatísticas Counter, autores etc). Además el fortalecimiento y creación de centros de desarrollo de OJS en las Universidades Latinoamericanas podría impulsionar el uso del sistema en su totalidad por los editores de la región.

Quantum biology. Simulazioni di trasferimento di energia in una struttura dimerica

La quantum biology (QB) è un campo di ricerca emergente che cerca di affronta- re fenomeni quantistici non triviali all’interno dei contesti biologici dotandosi di dati sperimentali di esplorazioni teoriche e tecniche numeriche. I sistemi biologici sono per definizione sistemi aperti, caldi,umidi e rumorosi, e queste condizioni sono per loro imprenscindibili; si pensa sia un sistema soggetto ad una veloce decoerenza che sopprime ogni dinamica quantistica controllata. La QB, tramite i principi di noise assisted transport e di antenna fononica sostiene che la presenza di un adeguato livello di rumore ambientale aumenti l’efficienza di un network di trasporto,inoltre se all’interno dello spettro ambientale vi sono specifici modi vibrazionali persistenti si hanno effetti di risonanza che rigenerano la coerenza quantistica. L’interazione ambiente-sistema è di tipo non Markoviano,non perturbativo e di forte non equi- librio, ed il rumore non è trattato come tradizionale rumore bianco. La tecnica numerica che per prima ha predetto la rigenerazione della coerenza all’interno di questi network proteici è stato il TEBD, Time Evolving Block Decimation, uno schema numerico che permette di simulare sistemi 1-D a molti corpi, caratterizzati da interazioni di primi vicini e leggermente entangled. Tramite gli algoritmi numerici di Orthopol l’hamiltoniana spin-bosone viene proiettata su una catena discreta 1-D, tenendo conto degli effetti di interazione ambiente-sistema contenuti nello spettro(il quale determina la dinamica del sistema).Infine si esegue l’evoluzione dello stato.

Strong Local Passivity in Finite Quantum Systems

Passive states of quantum systems are states from which no system energy can be extracted by any cyclic (unitary) process. Gibbs states of all temperatures are passive. Strong local (SL) passive states are defined to allow any general quantum operation, but the operation is required to be local, being applied only to a specific subsystem. Any mixture of eigenstates in a system-dependent neighborhood of a nondegenerate entangled ground state is found to be SL passive. In particular, Gibbs states are SL passive with respect to a subsystem only at or below a critical system-dependent temperature. SL passivity is associated in many-body systems with the presence of ground state entanglement in a way suggestive of collective quantum phenomena such as quantum phase transitions, superconductivity, and the quantum Hall effect. The presence of SL passivity is detailed for some simple spin systems where it is found that SL passivity is neither confined to systems of only a few particles nor limited to the near vicinity of the ground state.

Current in coherent quantum systems connected to mesoscopic Fermi reservoirs

We study particle current in a recently proposed model for coherent quantum transport. In this model, a system connected to mesoscopic Fermi reservoirs (meso-reservoir) is driven out of equilibrium by the action of super-reservoirs thermalized to prescribed temperatures and chemical potentials by a simple dissipative mechanism described by the Lindblad equation. We compare exact (numerical) results with theoretical expectations based on the Landauer formula.

Optimal unravellings for feedback control in linear quantum systems

For quantum systems with linear dynamics in phase space much of classical feedback control theory applies. However, there are some questions that are sensible only for the quantum case: Given a fixed interaction between the system and the environment what is the optimal measurement on the environment for a particular control problem? We show that for a broad class of optimal (state- based) control problems ( the stationary linear-quadratic-Gaussian class), this question is a semidefinite program. Moreover, the answer also applies to Markovian (current-based) feedback.

Mean field evolution in an open quantum system

In this thesis, we consider N quantum particles coupled to collective thermal quantum environments. The coupling is energy conserving and scaled in the mean field way. There is no direct interaction between the particles, they only interact via the common reservoir. It is well known that an initially disentangled state of the N particles will remain disentangled at times in the limit N -> [infinity]. In this thesis, we evaluate the η-body reduced density matrix (tracing over the reservoirs and the N - η remaining particles). We identify the main disentangled part of the reduced density matrix and obtain the first order correction term in 1/N. We show that this correction term is entangled. We also estimate the speed of convergence of the reduced density matrix as N -> [infinity]. Our model is exactly solvable and it is not based on numerical approximation.