Universal energy distribution of quasi-particles emitted in a local time dependent quench

We study the emission of quasi-particles in the scaling limit of the 1d Quantum Ising chain at the critical point perturbed by a time dependent local transverse field. We compute \it exactly \rm and for a \it generic \rm time dependence the average value of the transverse magnetization, its correlation functions, as well as the statistic of both the inclusive and exclusive work. We show that, except for a cyclic perturbation, the probability distribution of the work at low energies is a power law whose exponent is universal, i.e. does not depend on the specific time dependent protocol, but only on the final value attained by the perturbation.Comment: 5 pages, 1 figure, Published Versio

Effects of Entanglement in Controlled Dephasing

In controlled dephasing as a result of the interaction of a controlled environment (dephasor) and the system under observation (dephasee) the states of the two subsystems are entangled. Using as an example the ``Which Path Detector'', we discuss how the entanglement influences the controlled dephasing. In particular, we calculate the suppression $\nu$ of A-B oscillations as a function of the bias $eV$ applied to the QPC and the coupling $\Gamma$ of the QD to the leads. At low temperatures the entanglement produces a smooth crossover from $\nu \propto (eV/\Gamma)^2$, when $eV \ll \Gamma$ to $\nu \propto eV/\Gamma$, for $eV \gg \Gamma$.Comment: 4 pages, 1 figur

Quantum quenches in the Dicke model: statistics of the work done and of other observables

We study the statistics of the work done in a zero temperature quench of the coupling constant in the Dicke model describing the interaction between a gas of two level atoms and a single electromagnetic cavity mode. When either the final or the initial coupling constants approach the critical coupling $\lambda_c$ that separates the normal and superradiant phases of the system, the probability distribution of the work done displays singular behavior. The average work tends to diverge as the initial coupling parameter is brought closer to the critical value $\lambda_c$. In contrast, for quenches ending close to criticality, the distribution of work has finite moments but displays a sequence of edge singularities. This contrasting behavior is related to the difference between the processes of compression and expansion of a particle subject to a sudden change of its confining potential. We confirm this by studying in detail the time dependent statistics of other observables, such as the quadratures of the photons and the total occupation of the bosonic modes.Comment: 8 pages, 2 figure

Towards measuring Entanglement Entropies in Many Body Systems

We explore the relation between entanglement entropy of quantum many body systems and the distribution of corresponding, properly selected, observables. Such a relation is necessary to actually measure the entanglement entropy. We show that in general, the Shannon entropy of the probability distribution of certain symmetry observables gives a lower bound to the entropy. In some cases this bound is saturated and directly gives the entropy. We also show other cases in which the probability distribution contains enough information to extract the entropy: we show how this is done in several examples including BEC wave functions, the Dicke model, XY spin chain and chains with strong randomness

Relaxation, pre-thermalization and diffusion in a noisy Quantum Ising Chain

We study the dynamics of thermalization resulting from a time-dependent noise in a Quantum Ising Chain subject to a sudden quench of the transverse magnetic field. For weak noise the dynamics shows a pre-thermalized state at intermediate time scales, eventually drifting towards an asymptotic infinite temperature steady state characterized by diffusive behavior. By computing analytically the density of kinks, as well as the transverse and longitudinal magnetic field correlators, we characterize these two regimes, their observability and their signatures in the various physical quantities.Comment: 5 pages, 2 figures. Accepted for publication in PRB Rapid Communication

Modelos estatísticos para previsão de geada branca

TCC (graduação) - Universidade Federal de Santa Catarina. Centro de Ciências Agrárias. Curso de Agronomia.O objetivo do trabalho foi obter modelos estatísticos para a previsão de geada branca. Foram utilizados dados meteorológicos diários de temperatura mínima e temperatura média do ar das 18 h e 00 h (TMG - Tempo Médio de Greenwich) no período de maio a agosto de 2000 a 2015, de estações localizadas nos municípios de Campos Novos, Lages, Chapecó e São Joaquim, em Santa Catarina. Foi utilizada a regressão linear simples e polinomial para correlacionar as variáveis independentes (X), temperatura mínima, temperatura média, temperatura das 18 h e 00 h (TGM) do dia anterior (Ti-1), com a variável dependente (Y), temperatura mínima do dia presente (Tmin i). O índice de confiança foi utilizado para avaliar a confiabilidade da estimativa de temperatura mínima (Ti). A temperatura do ar a 00 h (TMG) foi a melhor variável preditora para a temperatura mínima (Tmin i). Os modelos estatísticos obtidos para previsão de temperatura mínima (Tmin i) apresentaram um desempenho ‘muito bom’. Em eventos de geada branca (Tmin ≤ 4°C), o acerto nas estimativas esteve entre 64,3% e 88,9%.The objective was to obtain statistical models for the prediction of hoarfrost. Were used daily weather data minimum temperature and average air temperature of 18 h and 00 h (GMT - Greenwich Mean Time) in the period May-August 2000 to 2015, of stations located in the cities of Campos Novos, Lages, Chapecó and São Joaquim, Santa Catarina. Was used Simple Linear Regression and Polynomial for correlating the independent variables (X), minimum temperature, mean temperature, temperature of 18 h and 00 h (GMT) on the previous day (Ti-1), with the dependent variable (Y), temperature minimum present day (Tmin i). The confidence index was used to assess the reliability of the estimated minimum temperature (Ti). The air temperature at 00 h (GMT) was the best predictor variable for the minimum temperature (Tmin i). Statistical models obtained for minimum temperature forecast (Tmin i) presented a performance of 'very good'. In hoarfrost events (Tmin ≤ 4 °C), the accuracy of estimates was between 64,3% and 88,9%