3,325 research outputs found
Shielding and localization in presence of long range hopping
We investigate a paradigmatic model for quantum transport with both
nearest-neighbor and infinite range hopping coupling (independent of the
position). Due to long range homogeneous hopping, a gap between the ground
state and the excited states can be induced, which is mathematically equivalent
to the superconducting gap. In the gapped regime, the dynamics within the
excited states subspace is shielded from long range hopping, namely it occurs
as if long range hopping would be absent. This is a cooperative phenomenon
since shielding is effective over a time scale which diverges with the system
size. We named this effect {\it Cooperative Shielding}. We also discuss the
consequences of our findings on Anderson localization. Long range hopping is
usually thought to destroy localization due to the fact that it induces an
infinite number of resonances. Contrary to this common lore we show that the
excited states display strong localized features when shielding is effective
even in the regime of strong long range coupling. A brief discussion on the
extension of our results to generic power-law decaying long range hopping is
also given. Our preliminary results confirms that the effects found for the
infinite range case are generic.Comment: 7 pages, 9 figur
The Topological Non-connectivity Threshold in quantum long-range interacting spin systems
Quantum characteristics of the Topological Non-connectivity Threshold (TNT),
introduced in F.Borgonovi, G.L.Celardo, M.Maianti, E.Pedersoli, J. Stat. Phys.,
116, 516 (2004), have been analyzed in the hard quantum regime. New interesting
perspectives in term of the possibility to study the intriguing
quantum-classical transition through Macroscopic Quantum Tunneling have been
addressed.Comment: contribution to NEXTSIGMAPHI 3r
Quantum Dynamical Effects as a Singular Perturbation for Observables in Open Quasi-Classical Nonlinear Mesoscopic Systems
We review our results on a mathematical dynamical theory for observables for
open many-body quantum nonlinear bosonic systems for a very general class of
Hamiltonians. We show that non-quadratic (nonlinear) terms in a Hamiltonian
provide a singular "quantum" perturbation for observables in some "mesoscopic"
region of parameters. In particular, quantum effects result in secular terms in
the dynamical evolution, that grow in time. We argue that even for open quantum
nonlinear systems in the deep quasi-classical region, these quantum effects can
survive after decoherence and relaxation processes take place. We demonstrate
that these quantum effects in open quantum systems can be observed, for
example, in the frequency Fourier spectrum of the dynamical observables, or in
the corresponding spectral density of noise. Estimates are presented for
Bose-Einstein condensates, low temperature mechanical resonators, and nonlinear
optical systems prepared in large amplitude coherent states. In particular, we
show that for Bose-Einstein condensate systems the characteristic time of
deviation of quantum dynamics for observables from the corresponding classical
dynamics coincides with the characteristic time-scale of the well-known quantum
nonlinear effect of phase diffusion.Comment: changed content
O uso da radiação gama como agente mutogênico para reduzir o ciclo vegetativo da cultivar BR 005R.
Quantum Fractal Fluctuations
We numerically analyse quantum survival probability fluctuations in an open,
classically chaotic system. In a quasi-classical regime, and in the presence of
classical mixed phase space, such fluctuations are believed to exhibit a
fractal pattern, on the grounds of semiclassical arguments. In contrast, we
work in a classical regime of complete chaoticity, and in a deep quantum regime
of strong localization. We provide evidence that fluctuations are still
fractal, due to the slow, purely quantum algebraic decay in time produced by
dynamical localization. Such findings considerably enlarge the scope of the
existing theory.Comment: revtex, 4 pages, 5 figure
Estimativas da capacidade geral e específica de combinação para alguns características agronômicas de hibridos F1 de sorgo, Sorghum bicolor (L.) Moench.
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