Temperature effects on a network of dissipative quantum harmonic oscillators: collective damping and dispersion processes

In this paper we extend the results presented in (de Ponte, Mizrahi and Moussa 2007 Phys. Rev. A 76 032101) to treat quantitatively the effects of reservoirs at finite temperature in a bosonic dissipative network: a chain of coupled harmonic oscillators whatever its topology, i.e., whichever the way the oscillators are coupled together, the strength of their couplings and their natural frequencies. Starting with the case where distinct reservoirs are considered, each one coupled to a corresponding oscillator, we also analyze the case where a common reservoir is assigned to the whole network. Master equations are derived for both situations and both regimes of weak and strong coupling strengths between the network oscillators. Solutions of these master equations are presented through the normal ordered characteristic function. These solutions are shown to be significantly involved when temperature effects are considered, making difficult the analysis of collective decoherence and dispersion in dissipative bosonic networks. To circumvent these difficulties, we turn to the Wigner distribution function which enables us to present a technique to estimate the decoherence time of network states. Our technique proceeds by computing separately the effects of dispersion and the attenuation of the interference terms of the Wigner function. A detailed analysis of the dispersion mechanism is also presented through the evolution of the Wigner function. The interesting collective dispersion effects are discussed and applied to the analysis of decoherence of a class of network states. Finally, the entropy and the entanglement of a pure bipartite system are discussed.

Action of the gravitational field on the dynamical Casimir effect

In this paper, we analyze the action of the gravitational field on the dynamical Casimir effect. We consider a massless scalar field confined in a cuboid cavity placed in a gravitational field described by a static and diagonal metric. With one of the plane mirrors of the cavity allowed to move, we compute the average number of particles created inside the cavity by means of the Bogoliubov coefficients computed through perturbative expansions. We apply our result to the case of an oscillatory motion of the mirror, assuming a weak gravitational field described by the Schwarzschild metric. The regime of parametric amplification is analyzed in detail, demonstrating that our computed result for the mean number of particles created agrees with specific associated cases in the literature. Our results, obtained in the framework of the perturbation theory, are restricted, under resonant conditions, to a short-time limit.

Storing quantum states in bosonic dissipative networks

By considering a network of dissipative quantum harmonic oscillators, we deduce and analyse the optimum topologies which are able to store quantum superposition states, protecting them from decoherence, for the longest period of time. The storage is made dynamically, in that the states to be protected evolve through the network before being retrieved back in the oscillator where they were prepared. The decoherence time during the dynamic storage process is computed and we demonstrate that it is proportional to the number of oscillators in the network for a particular regime of parameters.

Switching off the reservoir through nonstationary quantum systems

In this paper, we demonstrate that the inevitable action of the environment can be substantially weakened when considering appropriate nonstationary quantum systems. Beyond protecting quantum states against decoherence, an oscillating frequency can be engineered to make the system-reservoir coupling almost negligible. Differently from the program for engineering reservoir and similarly to the schemes for dynamical decoupling of open quantum systems, our technique does not require previous knowledge of the state to be protected. However, differently from the previously-reported schemes for dynamical decoupling, our technique does not rely on the availability of tailored external pulses acting faster than the shortest timescale accessible to the reservoir degree of freedom.

A general treatment of geometric phases and dynamical invariants

Based only on the parallel-transport condition, we present a general method to compute Abelian or non-Abelian geometric phases acquired by the basis states of pure or mixed density operators, which also holds for nonadiabatic and noncyclic evolution. Two interesting features of the non-Abelian geometric phase obtained by our method stand out: i) it is a generalization of Wilczek and Zee`s non-Abelian holonomy, in that it describes nonadiabatic evolution where the basis states are parallelly transported between distinct degenerate subspaces, and ii) the non-Abelian character of our geometric phase relies on the transitional evolution of the basis states, even in the nondegenerate case. We apply our formalism to a two-level system evolving nonadiabatically under spontaneous decay to emphasize the non- Abelian nature of the geometric phase induced by the reservoir. We also show, through the generalized invariant theory, that our general approach encompasses previous results in the literature. Copyright (c) EPLA, 2008.

Estimating losses in an entanglement concentration scheme using the phenomenological operator approach to dissipation in cavity quantum electrodynamics

In a previous paper, we developed a phenomenological-operator technique aiming to simplify the estimate of losses due to dissipation in cavity quantum electrodynamics. In this paper, we apply that technique to estimate losses during an entanglement concentration process in the context of dissipative cavities. In addition, some results, previously used without proof to justify our phenomenological-operator approach, are now formally derived, including an equivalent way to formulate the Wigner-Weisskopf approximation.

Spontaneous recoherence of quantum states after decoherence

In this work, we identify the set of time-dependent pure states building the statistical mixture to which a system, initially in a pure state, is driven by the reservoir. This set of time-dependent pure states, composing what we term a pure basis, are those that diagonalize the reduced density operator of the system. Next, we show that the evolution of the pure-basis states reveals an interesting phenomenon as the system, after decoherence, evolves toward the equilibrium: the spontaneous recoherence of quantum states. Around our defined recoherence time, the statistical mixture associated with a special kind of initial states termed even-symmetric, spontaneously undergoes a recoherence process, by which the initial state of the system emerges from the mixture except for its reduced excitation drained into the reservoir. This phenomenon reveals that the reservoir only shuffle the original information carried out by the initial state of the system instead of erasing it. Moreover, as the spontaneously recohered state occurs only for asymptotic time, we also present a protocol to extract it from the mixture through specific projective measurements. The password to retrieve the original information stems is the knowledge of both the initial state itself and the associated pure basis. A definition of the decoherence time of an N-state superposition is also presented.

The double Caldeira-Leggett model: Derivation and solutions of the master equations, reservoir-induced interactions and decoherence

In this paper we analyze the double Caldeira-Leggett model: the path integral approach to two interacting dissipative harmonic oscillators. Assuming a general form of the interaction between the oscillators, we consider two different situations: (i) when each oscillator is coupled to its own reservoir, and (ii) when both oscillators are coupled to a common reservoir. After deriving and solving the master equation for each case, we analyze the decoherence process of particular entanglements in the positional space of both oscillators. To analyze the decoherence mechanism we have derived a general decay function, for the off-diagonal peaks of the density matrix, which applies both to common and separate reservoirs. We have also identified the expected interaction between the two dissipative oscillators induced by their common reservoir. Such a reservoir-induced interaction, which gives rise to interesting collective damping effects, such as the emergence of relaxation- and decoherence-free subspaces, is shown to be blurred by the high-temperature regime considered in this study. However, we find that different interactions between the dissipative oscillators, described by rotating or counter-rotating terms, result in different decay rates for the interference terms of the density matrix. (C) 2010 Elsevier B.V. All rights reserved.

Quasi-perfect state transfer in a bosonic dissipative network

In this paper we propose a scheme for quasi-perfect state transfer in a network of dissipative harmonic oscillators. We consider ideal sender and receiver oscillators connected by a chain of nonideal transmitter oscillators coupled by nearest-neighbour resonances. From the algebraic properties of the dynamical quantities describing the evolution of the network state, we derive a criterion, fixing the coupling strengths between all the oscillators, apart from their natural frequencies, enabling perfect state transfer in the particular case of ideal transmitter oscillators. Our criterion provides an easily manipulated formula enabling perfect state transfer in the special case where the network nonidealities are disregarded. We also extend such a criterion to dissipative networks where the fidelity of the transferred state decreases due to the loss mechanisms. To circumvent almost completely the adverse effect of decoherence, we propose a protocol to achieve quasi-perfect state transfer in nonideal networks. By adjusting the common frequency of the sender and the receiver oscillators to be out of resonance with that of the transmitters, we demonstrate that the sender`s state tunnels to the receiver oscillator by virtually exciting the nonideal transmitter chain. This virtual process makes negligible the decay rate associated with the transmitter line at the expense of delaying the time interval for the state transfer process. Apart from our analytical results, numerical computations are presented to illustrate our protocol.

Utvärdering av Elektronisk fakturahantering inom Banverket

Vår uppdragsgivare Banverket efterfrågade en utvärdering av elektronisk fakturahantering(EFH) vid Banverket som infördes för cirka två år sedan. Det finns några olika verktyg för EFH, skanning av pappersfakturor är ett av de verktygen som Banverket använder för att hantera pappersfakturor från olika leverantörer. Vårt mål med uppsatsen var att analysera vilken effekt användningen av EFH får för Banverket.I vår analys studerades effekter av det införda systemet för elektronisk fakturahantering. Uppsatsen har gjorts med hjälp av en kvalitativ undersöknings metod, analysmetoden FA/SIM samt litteraturstudier inom ämnet. Vi har intervjuat personal vid Banverket Produktion och Banregioner i Malmö samt Stockholm. Vi har även intervjuat personal vid HK, Projektering och Telenät i Borlänge.Efter vår analys har vi kommit fram till att det finns stora ekonomiska vinster med elektronisk fakturahantering, men även vinster som inte är direkt mätbara. De viktigaste effekterna är att inga fakturor kommer bort efter de har skannats in och systemet har hela tiden reda på var i flödet fakturan befinner sig, det vill säga bättre kontroll har vunnits. Genom införandet av EFH har flera arbetsmoment försvunnit eller automatiserats och hanteringen av fakturor har förenklats, vilket bidrar till mindre kostnader för hantering av fakturor. Med EFH behöver användarna inte ta kopior av fakturor eftersom de hela tiden finns i systemet. När det gäller minskad dröjsmålsränta har vi kommit fram till att Banverket bör ha minskat kostnaderna för dröjsmålsränta.

En jämförande studie av olika Oracle verktyg.

Idag finns det många företag som erbjuder olika program/databaser som har till uppgift att lagraoch hantera data. Oracle är världens näst största mjukvaruföretag. Oracles databas genererar ungefär 75 % av deras inkomst.De senaste 40 åren har databashantering utvecklats från enkelt filsystem tillobjektrelationsdatabas, vilket har medfört att allt fler företag idag erbjuder verktyg som databasutvecklare kan arbeta med. Verktygen underlättar själva databashanteringen. Det är mångaföretag som erbjuder olika sorters verktyg och databas utvecklaren, eller själva databasföretaget,får svårt att skilja på verktygen. Utbudet av verktyg är så omfattande att det är näst intill omöjligtatt ha kännedom om alla.Syftet med denna uppsats är att undersöka vilket verktyg en Oracle-utvecklare bör använda sigav. Att jämföra olika SQL och PL/SQL verktyg, samt lämna en rekommendation om vilket/vilkaverktyg som är bäst att använda ur olika perspektiv. Vid jämförelsen laddade jag hem och testadede olika verktygen utifrån vissa kriterier. Jag kontaktade även fyra företag för att få svar på frågan utifrån företagens perspektiv. Tre av företagen svarade på mina enkäter, medan ett av företagen svarade muntligt på mina frågor via telefonen.Då jag genomförde denna studie kom jag fram till slutsatsen att alla verktyg i stort sett har samma grundfunktioner. Valet av verktyg styrs av hur många extra funktioner utvecklaren är villig betala för. Det är dock utvecklaren själv som måste avgöra vilket verktyg som passar just honom. Det verktyg som är ledande är Toad och detta verktyg passar bäst för experter. För enklare funktioner har det framkommit av enkäterna att SQL*Plus används.

Road Sign Recognition based onInvariant Features using SupportVector Machine

Since last two decades researches have been working on developing systems that can assistsdrivers in the best way possible and make driving safe. Computer vision has played a crucialpart in design of these systems. With the introduction of vision techniques variousautonomous and robust real-time traffic automation systems have been designed such asTraffic monitoring, Traffic related parameter estimation and intelligent vehicles. Among theseautomatic detection and recognition of road signs has became an interesting research topic.The system can assist drivers about signs they don’t recognize before passing them.Aim of this research project is to present an Intelligent Road Sign Recognition System basedon state-of-the-art technique, the Support Vector Machine. The project is an extension to thework done at ITS research Platform at Dalarna University [25]. Focus of this research work ison the recognition of road signs under analysis. When classifying an image its location, sizeand orientation in the image plane are its irrelevant features and one way to get rid of thisambiguity is to extract those features which are invariant under the above mentionedtransformation. These invariant features are then used in Support Vector Machine forclassification. Support Vector Machine is a supervised learning machine that solves problemin higher dimension with the help of Kernel functions and is best know for classificationproblems.

Estimulação transcraniana por corrente contínua e a flutuação de força em idosas durante exercício isométrico

The fluctuacion force has been increasingly used in studies with elderly as a good predictor of performance and functionality of the motor. However, most analyzes the fluctuation of force in one session. Thus, identifying the minimum amount of sessions needed for familiarization with the fluctuation strength in isometric exercise become relevant. Furthermore, to investigate the effects of applying transcranial direct current stimulation (tDCS) associated with regular exercise on rates fluctuation task force is extremely important. In the first experiment, volunteers were subjected to a protocol marked by a familiarization session to establish the parameters of VCM and eight sessions with intensity of 30% MVC in office. It was observed that two familiarization sessions are required so there is a fluctuation stabilizing force. In experiment II, subjects performed an isometric contraction before and after applying tDCS (cathode, anode and sham) applied to M1. ETCC anodic effectively contributed to reducing the fluctuation of force during isometric exercise in the elderly, while the cathodic caused the increased levels of strength fluctuation. It was concluded that there is a need to implement a familiarization protocol with at least two sessions to avoid possible misunderstandings of measurements in tests of fluctuacion force. Besides that tDCS interfered with the behavior of the oscillations of force, with cathodic promoting increased fluctuation strength and anodic contributed to greater stability, demonstrating the potential of this technique neuromodulation associated with exercise as rehabilitation tools

A influência da estimulação transcrâniana por corrente contínua nos parâmetros de dano muscular induzido pelo exercício

A estimulação transcraniana por corrente contínua (ETCC) é uma técnica não invasiva que apresenta características anti-fadigante e analgésica. Com o objetivo de testar seus efeitos sobre a diminuição da força e do aparecimento da dor muscular de início tardio (DMIT), apresentados após um evento de dano muscular induzido pelo exercício (DMIE), foi utilizado um estudo clínico de caráter experimental, controlado, randomizado e duplo-cego. A amostra foi composta por 24 jovens do sexo masculino, aparentemente saudáveis (19,7±1,8 anos; 23,6±3,65 IMC), os quais foram alocada, de forma aleatória e estratificada, nos seguintes grupos: G1: grupo controle; G2: grupo de estimulação após o dano e G3: grupo com estimulação antes e após o dano muscular. Os dados foram submetidos à estatística descritiva e análise de variância ANOVA, adotando-se um nível de significância de 5%. O aumento nos níveis séricos de CK (56.18%) e LDH (24,15%) comprovou a ocorrência do DMIE. Em contrapartida, após a análise de variância para comparação dos tratamentos aplicados, pode-se observar que não houve diferenças significativas nos níveis de CK (p= 0,3514) e força muscular (p= 0,9702). A DMIT transcorreu como esperado, mas sem diferença significativa entre os grupos (p= 0,4861). Estes dados demonstraram que a ETCC não foi capaz de modular a DMIT e a diminuição da força muscular após o DMIE em jovens aparentemente saudáveis