Correction to the geometric phase by structured environments: the onset of non-Markovian effects

We study the geometric phase of a two-level system under the presence of a structured environment, particularly analysing its correction with the ohmicity parameter $s$ and the onset of non-Markovianity. We firstly examine the system coupled to a set of harmonic oscillators and studied the decoherence factor as function of the environment's ohmicity parameter. Secondly, we propose the two-level system coupled to a non-equilibrium environment, and show that these environments display non-Markovian effects for all values of the ohmicity parameter. The geometric phase of the two-level system is therefore computed under the presence of both types of environment. The correction to the unitary geometric phase is analysed in both, Markovian and non-Markovian regimes. Under Markovian environments, the correction induced on the system's phase is mainly ruled by the coupling constant between the system and the environment, while in the non-Markovian regime, memory effects seem to trigger a significant correction to the unitary geometric phase. The result is significant to the quantum information processing based on the geometric phase in quantum open systemsComment: 7 figures. Accepted for publication in Phys. Rev. A. arXiv admin note: text overlap with arXiv:1303.493

Decoherence in composite quantum open systems: the effectiveness of unstable degrees of freedom

The effect induced by an environment on a composite quantum system is studied. The model considers the composite system as comprised by a subsystem A coupled to a subsystem B which is also coupled to an external environment. We study all possible four combinations of subsystems A and B made up with a harmonic oscillator and an upside down oscillator. We analyzed the decoherence suffered by subsystem A due to an effective environment composed by subsystem B and the external reservoir. In all the cases we found that subsystem A decoheres even though it interacts with the environment only through its sole coupling to B. However, the effectiveness of the diffusion depends on the unstable nature of subsystem A and B. Therefore, the role of this degree of freedom in the effective environment is analyzed in detailComment: 20 pages, 4 figures. Version to appear in Int. J. Mod. Phys.

Fluent Logic Workflow Analyser: A Tool for The Verification of Workflow Properties

In this paper we present the design and implementation, as well as a use case, of a tool for workflow analysis. The tool provides an assistant for the specification of properties of a workflow model. The specification language for property description is Fluent Linear Time Temporal Logic. Fluents provide an adequate flexibility for capturing properties of workflows. Both the model and the properties are encoded, in an automated way, as Labelled Transition Systems, and the analysis is reduced to model checking.Comment: In Proceedings LAFM 2013, arXiv:1401.056

Decoherence of a solid-state qubit by different noise correlation spectra

The interaction between solid-state qubits and their environmental degrees of freedom produces non-unitary effects like decoherence and dissipation. Uncontrolled decoherence is one of the main obstacles that must be overcome in quantum information processing. We study the dynamically decay of coherences in a solid-state qubit by means of the use of a master equation. We analyse the effects induced by thermal Ohmic environments and low-frequency 1/f noise. We focus on the effect of longitudinal and transversal noise on the superconducting qubit's dynamics. Our results can be used to design experimental future setups when manipulating superconducting qubits.Comment: 14 pages, 9 figures. Version to appear in Physics Letters A. arXiv admin note: text overlap with arXiv:0809.4716 by other author

Mortalidad y morbilidad cardiovascular

En la actualidad se producen en España más de 120.000 muertes y más de 5 millones de estancias hospitalarias por enfermedades cardiovasculares al año. Por ello, las enfermedades cardiovasculares constituyen la primera causa de muerte y hospitalización en la población española. La enfermedad isquémica del corazón es la que ocasiona un mayor número de muertes cardiovasculares (31% en total, un 39% en varones y 24% en mujeres) en España. Este fenómeno se empezó a dar en el año 1996, y se debe al mayor descenso relativo de la mortalidad cerebrovascular respecto a la coronaria, invirtiéndose el llamado patrón mediterráneo en el que predominaba la enfermedad cerebrovascular. Cabe destacar que en los varones empieza a predominar la enfermedad isquémica del corazón sobre la cerebrovascular casi diez años antes, en 1987. En las mujeres el peso que tienen las enfermedades del aparato circulatorio en la mortalidad proporcional por todas las causas es mucho más importante que en los varones, ya que en las mujeres ocasionan cerca de la mitad de las muertes (40%) mientras que en los varones sólo representa un tercio de ellas (30%). A pesar de que la tasa bruta de mortalidad cardiovascular es mayor en las mujeres (328 por 100.000) que en los varones (284 por 100.000), las tasas específicas por grupo de edad son mayores en los varones excepto a partir de los 84 años de edad. Del mismo modo, la mortalidad ajustada por edad por las enfermedades cardiovasculares es más alta en los varones que en las mujeres. Esto se debe al mayor riesgo cardiovascular de los varones, reflejado en las tasas específicas de edad, y a que la enfermedad cardiovascular es mucho más frecuente en las edades avanzadas de la vida, donde el número de mujeres es muy superior al de varones. La tasa de mortalidad cardiovascular aumenta enormemente a medida que se incrementa la edad, siendo superior a mil por 100.000 habitantes en las personas mayores de 70 años (cuando la tasa bruta para todas las edades es de 306 por 100.000 habitantes en 2001). Hay importantes diferencias geográficas en la mortalidad cardiovascular en España, presentándose los valores más altos en Canarias, y las regiones peninsulares del sur y levante. Asumiendo que una parte importante de las mismas se deben a factores ambientales, estas diferencias geográficas sugieren un importante potencial de prevención de las enfermedades cardiovasculares en España. Comparando las tasas de mortalidad ajustadas por edad de España con las de otros países occidentales se observa que para el total de las enfermedades del aparato circulatorio y para la enfermedad isquémica del corazón, España tiene unas tasas relativamente más bajas; en cuanto a la mortalidad por enfermedad cerebrovascular ocupa una posición intermedia-baja. Las tasas ajustadas de mortalidad por enfermedades del aparato circulatorio han disminuido en España desde 1975. En el período 1985-1995 descendieron un 26%, con un descenso medio anual del 2,4% (2,3% en varones y 2,5% en mujeres). La mayor parte del descenso de la mortalidad cardiovascular total se debe a una disminución media anual del 3,2% en la mortalidad cerebrovascular. Por tanto, el riesgo de morir por las enfermedades del aparato circulatorio está disminuyendo en España desde mediados de los años setenta, sobre todo debido al descenso de la mortalidad cerebrovascular. Sin embargo, y debido fundamentalmente al envejecimiento de la población, el número de muertes por coronariopatía ha aumentado. Por ello, el impacto demográfico, sanitario y social de estas enfermedades aumentará a lo largo de las próximas décadas. Se prevé un aumento en el número de hospitalizaciones por estas enfermedades en los próximos años, como consecuencia del desarrollo tecnológico que permitirá ofrecer a los pacientes nuevos instrumentos diagnósticos y terapéuticos, de la mayor supervivencia de los pacientes con estos problemas de salud y, en menor medida, del envejecimiento de la población española

Macroscopic tunneling, decoherence and noise-induced activation

We study the effects of the environment at zero temperature on tunneling in an open system described by a static double-well potential. We show that the evolution of the system in an initial Schrodinger cat state, can be summarized in terms of three main physical phenomena, namely decoherence, quantum tunneling and noise-induced activation. Using large-scale numerical simulations, we obtain a detailed picture of the main stages of the evolution and of the relevant dynamical processesComment: Contribution to the Proceedings of DICE'0

Visibility Fringe Reduction Due to Noise-Induced Effects: Microscopic Approach to Interference Experiments

Decoherence is the main process behind the quantum to classical transition. It is a purely quantum mechanical effect by which the system looses its ability to exhibit coherent behavior. The recent experimental observation of diffraction and interference patterns for large molecules raises some interesting questions. In this context, we identify possible agents of decoherence to take into account when modeling these experiments and study theirs visible (or not) effects on the interference pattern. Thereby, we present an analysis of matter wave interferometry in the presence of a dynamic quantum environment and study how much the visibility fringe is reduced and in which timescale the decoherence effects destroy the interference of massive objects. Finally, we apply our results to the experimental data reported on fullerenes and cold neutrons.Comment: 14 pages, 5 figures. Version to appear in Mod. Phys.

Geometric phases in open systems: an exact model to study how they are corrected by decoherence

We calculate the geometric phase for an open system (spin-boson model) which interacts with an environment (ohmic or nonohmic) at arbitrary temperature. However there have been many assumptions about the time scale at which the geometric phase can be measured, there has been no reported observation yet for mixed states under nonunitary evolution. We study not only how they are corrected by the presence of the different type of environments but also estimate the corresponding times at which decoherence becomes effective. These estimations should be taken into account when planning experimental setups to study the geometric phase in the nonunitary regime, particularly important for the application of fault-tolerant quantum computation.Comment: Revtex 4, 5 pages, one eps figure. Version Publishe

Interpretable models in machine learning

The research and development on machine learning has exploded in recent years due to the revolution of neural networks, which have become the greatest hope in the field of artificial intelligence after the improvements in hardware performance and the availability of high amounts of data. Nevertheless, it appears that advancements have been slowed down recently, probably because neural networks are reaching their precision limits. Moreover, neural networks have an imperfection that has not been remarked frequently: they are a black box in which it is not possible to understand the precision procedure of the network. In consequence, despite their precision, they do not provide us with strong arguments to justify their predictions. Decision trees, on the other hand, are a really interpretable model, though little precise. The objective of the study of this project is the creation of a mixed model between neural networks and decision trees: the deciduous decision tree. This prediction model combines the structure of a decision tree and the predictive capacities of the neural networks, aiming at reaching a custom intermediate point in the dichotomy between precision and interpretability. The results obtained after the analysis of several experiments conducted to the deciduous decision tree reveal that, even with a little loss of precision, the gain of interpretability from the decisions that are made in the tree compensates this loss. Therefore, this new model can be a starting point to make machine learning models be more interpretable, which can be extremely useful in a huge variety of fields, such as medicine, sociology, meteorology, law, etc