Quantum Fluctuations
Mostrando 1-12 de 45 artigos, teses e dissertações.
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1. Exact photocount statistics : lasers near threshold
A previously constructed laser model with quantum (noncommuting) noise sources was shown to lead near threshold to a quantum rotating-wave Van der Pol oscillator. A full dynamical correspondence between quantum and classical random processes allows one to compute the average of any time-ordered, normal-ordered operator function by averaging the associated fu
Publicado em: 2011
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2. Emaranhamento tripartite no oscilador paramétrico ótico / Tripartite entanglement in the optical parametric oscillator
We present in this work the first experimental verification of entanglement between the, signal, idler and reflected pump beams, generated by an Optical Parametric Oscillator (OPO) above the threshold. Using the criterion of sum of variances, proposed by van Loock and Furusawa, we obtained results that indicate the existence of tripartite entanglement in our
Publicado em: 2009
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3. Geometria, Topologia e Elasticidade: aplicações a membranas e outros sistemas bidimensionais
Geometry, topology and elasticity are found in various branchs of physics and they play important roles in the understanding of many physical phenomena. In this work, we present three diferent systems where we can see such importance. First, a quantum neutral particle, constrained to move on a conical surface, is used as a toy model to explore bound states d
Publicado em: 2009
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4. Quantum percolation of one-electron states in power-law diluted chains
We investigate the nature of one-electron eigenstates in power-law diluted chains for which the probability of occurrence of a bond between sites separated by a distance r decays as p(r) = 1/r1+sigma. Using an exact diagonalization scheme on finite chains, we compute the spreading of an initially localized wave-packet, the time dependent participation number
Brazilian Journal of Physics. Publicado em: 2008-03
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5. Multicolor Quantum Correlations in the Optical Parametric Oscillator / Correlações quânticas multicolores no oscilador paramétrico ótico
We have investigated the collective quantum properties of the three bright light beams produced by an optical parametric oscillator (OPO) operating above threshold, named pump, signal, and idler. We have analyzed experimentally their intensity and phase quantum fluctuations, and how they are correlated. For the first time, we have observed the existence of p
Publicado em: 2008
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6. On a gravitational cutoff for the vacuum energy
A possible connection between the energy W of the vacuum fluctuations of quantum fields and gravity in "empty space" is conjectured in this paper using a natural cutoff of high momenta with the help of the gravitational radius of the vacuum region considered. We found that below some "critical" length L = 1 mm the pressure sigma is one third of the energy de
Brazilian Journal of Physics. Publicado em: 2006-06
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7. FIRST-ORDER TRANSITION IN THE FERMIONIC ISING SPIN GLASS MODEL IN A TRANSVERSE FIELD / TRANSIÇÕES DE PRIMEIRA ORDEM NO MODELO VIDRO DE SPIN ISING FERMIÔNICO EM UM CAMPO TRANSVERSO
The present work analyzes the fermionic Ising spin glass model in a transverse magnetic field. The problem is written in the Grand Canonical ensemble with the spin operators represented by bilinear combinations of fermionic fields. The transverse field is a spin "flip" mechanism and inserts quantum fluctuations, which can lead the transition temperature Tj t
Publicado em: 2006
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8. PRESSURE-TEMPERATURE-COMPOSITION PHASE DIAGRAM OF THE HEAVY FERMION COMPOUND CE2RH(1−X)IR(X)IN8 / DIAGRAMA DE FASES PRESSÃO-COMPOSIÇÃO-TEMPERATURA DO COMPOSTO FÉRMION PESADO CE2RH(1−X)IR(X)IN8
Heavy fermion compounds behave differently from typical metals at low temperatures, where the phenomena that arise due to the correlation between conduction electrons and the f ions of the lattice become evident. An increased effective electronic mass that can reach values as high as hundreds of times the free electron mass and the coexistence of magnetic or
Publicado em: 2006
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9. Dynamical properties in quantum many body systems / Propriedades dinamicas em sistemas quanticos de muitos corpos
Os sistemas quânticos de spin são caracterizados por espaços de estados muito grandes, cujas dimensões crescem exponencialmente com o número de partículas. Se após a preparação do estado inicial, o sistema for mantido isolado de variáveis externas, desenvolve-se uma evolução temporal unitária prescrita pela equação de Schrödinger ou pela equa
Publicado em: 2006
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10. Estudo de interferência de elétrons em dispositivos mesoscópicos no limite Hall quântico
In this work we introduce the basic concepts required to understand how electronic interferometers work. The interferometers are semiconductor devices based in GaAs/AlGaAs heterojunctions where a high mobility two-dimensional electron gas is formed. The electron gas is confined in a small region of dimension comparable to its Fermi wavelength. In a high magn
Publicado em: 2006
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11. Quantum correlations in inflationary spectra and violation of bell inequalities
In spite of the macroscopic character of the fluctuation amplitudes, we show that the standard inflationary distribution of primordial density fluctuations still exhibits inherently quantum mechanical correlations (which cannot be mimicked by any classical stochastic ensemble). To this end, we propose a Gedanken experiment for which certain Bell inequalities
Brazilian Journal of Physics. Publicado em: 2005-12
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12. Big extra dimensions make lambda too small
I argue that the true quantum gravity scale cannot be much larger than the Planck length, because if it were then the quantum gravity-induced fluctuations in L would be insufficient to produce the observed cosmic "dark energy". If one accepts this argument, it rules out scenarios of the "large extra dimensions" type. I also point out that the relation betwee
Brazilian Journal of Physics. Publicado em: 2005-06