Analytical treatment of stabilization

We present a summarizing account of a series of investigations whose central topic is to address the question whether atomic stabilization exists in an analytical way. We provide new aspects on several issues of the matter in the theoretical context when the dynamics is described by the Stark Hamiltonian. The main outcome of these studies is that the governing parameters for this phenomenon are the total classical momentum transfer and the total classical displacement. Whenever these two quantities vanish, asymptotically weak stabilization does exist. For all other situations we did not find any evidence for stabilization. We found no evidence that strong stabilization might occur. Our results agree qualitatively with the existing experimental findings

Robustness of bipartite Gaussian entangled beams propagating in lossy channels

Subtle quantum properties offer exciting new prospects in optical communications. Quantum entanglement enables the secure exchange of cryptographic keys and the distribution of quantum information by teleportation. Entangled bright beams of light attract increasing interest for such tasks, since they enable the employment of well-established classical communications techniques. However, quantum resources are fragile and undergo decoherence by interaction with the environment. The unavoidable losses in the communication channel can lead to a complete destruction of useful quantum properties -- the so-called "entanglement sudden death". We investigate the precise conditions under which this phenomenon takes place for the simplest case of two light beams and demonstrate how to produce states which are robust against losses. Our study sheds new light on the intriguing properties of quantum entanglement and how they may be tamed for future applications.Comment: To be published - Nature Photonic

Non-Hermitian Hamiltonians with real eigenvalues coupled to electric fields: from the time-independent to the time dependent quantum mechanical formulation

We provide a reviewlike introduction into the quantum mechanical formalism related to non-Hermitian Hamiltonian systems with real eigenvalues. Starting with the time-independent framework we explain how to determine an appropriate domain of a non-Hermitian Hamiltonian and pay particular attention to the role played by PT-symmetry and pseudo-Hermiticity. We discuss the time-evolution of such systems having in particular the question in mind of how to couple consistently an electric field to pseudo-Hermitian Hamiltonians. We illustrate the general formalism with three explicit examples: i) the generalized Swanson Hamiltonians, which constitute non-Hermitian extensions of anharmonic oscillators, ii) the spiked harmonic oscillator, which exhibits explicit supersymmetry and iii) the -x^4-potential, which serves as a toy model for the quantum field theoretical phi^4-theory.Comment: 14 pages, 3 figures, to appear in Laser Physics, minor typos correcte

Características físicas e físico-químicas de passiflora alata com desenvolvimento e maturação na época seca.

O mercado para alimentos saudáveis, mais nutritivos e com propriedades funcionais vem crescendo ano a ano. O gênero Passiflora conta com cerca de 150 a 200 espécies brasileiras, das quais 70 produzem frutos que podem ser aproveitados direta ou indiretamente como alimento (FALEIRO et. al. 2008). Além do grande número de espécies dentro do gênero, existe grande variabilidade intra-específica. Esta variabilidade é importante para os programas de melhoramento genético (FALEIRO et. al. 2008; COSTA, 2008). As polpas das espécies silvestres e variedades comerciais apresentam substâncias importantes na prevenção de doenças como flavanóides, minerais, carotenóides e vitamina C (COSTA; TUPINAMBÁ, 2005, COSTA, 2008; WONDRACEK, 2009). Dentre elas se destaca os maracujás doce Passiflora alata muito apreciada no consumo “in natura”. Esta espécie apresenta antioxidantes importantes para a saúde e também pode ser fonte de minerais (COSTA, 2008, COSTA; TUPINAMBÁ, 2005). Vários fatores podem interferir na qualidade da polpa, como por exemplo, a variedade local de plantio, época de produção dos frutos, maturação dos frutos, e armazenamento (COSTA, 2008, COHEN et al, 2008). O trabalho teve por finalidade avaliar as características físicas e físico-químicas das variedades P. alata N2, D e J da Embrapa Cerrados que tiveram desenvolvimento no período seco, com foco no melhoramento genético para características de interesse funcional

Disentanglement in Bipartite Continuous-Variable Systems

Entanglement in bipartite continuous-variable systems is investigated in the presence of partial losses, such as those introduced by a realistic quantum communication channel, e.g. by propagation in an optical fiber. We find that entanglement can vanish completely for partial losses, in a situa- tion reminiscent of so-called entanglement sudden death. Even states with extreme squeezing may become separable after propagation in lossy channels. Having in mind the potential applications of such entangled light beams to optical communications, we investigate the conditions under which entanglement can survive for all partial losses. Different loss scenarios are examined and we derive criteria to test the robustness of entangled states. These criteria are necessary and sufficient for Gaussian states. Our study provides a framework to investigate the robustness of continuous-variable entanglement in more complex multipartite systems.Comment: Phys. Rev. A (in press

Time evolution of non-Hermitian Hamiltonian systems

We provide time-evolution operators, gauge transformations and a perturbative treatment for non-Hermitian Hamiltonian systems, which are explicitly time-dependent. We determine various new equivalence pairs for Hermitian and non-Hermitian Hamiltonians, which are therefore pseudo-Hermitian and in addition in some cases also invariant under PT-symmetry. In particular, for the harmonic oscillator perturbed by a cubic non-Hermitian term, we evaluate explicitly various transition amplitudes, for the situation when these systems are exposed to a monochromatic linearly polarized electric field.Comment: 25 pages Latex, 1 eps figure, references adde

Odynophagia and neck pain after exercise

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