4,895 research outputs found
Quantum Markovian activated surface diffusion of interacting adsorbates
A quantum Markovian activated atom-surface diffusion model with interacting
adsorbates is proposed for the intermediate scattering function, which is shown
to be complex-valued and factorizable into a classical-like and a
quantum-mechanical factor. Applications to the diffusion of Na atoms on flat
(weakly corrugated) and corrugated-Cu(001) surfaces at different coverages and
surface temperatures are analyzed. Quantum effects are relevant to diffusion at
low surface temperatures and coverages even for relatively heavy particles,
such as Na atoms, where transport by tunneling is absent.Comment: 6 pages, 4 figure
Vacuum fluctuations and the conditional homodyne detection of squeezed light
Conditional homodyne detection of quadrature squeezing is compared with
standard nonconditional detection. Whereas the latter identifies
nonclassicality in a quantitative way, as a reduction of the noise power below
the shot noise level, conditional detection makes a qualitative distinction
between vacuum state squeezing and squeezed classical noise. Implications of
this comparison for the realistic interpretation of vacuum fluctuations
(stochastic electrodynamics) are discussed.Comment: 14 pages, 7 figures, to appear in J. Opt. B: Quantum Semiclass. Op
Phase-dependent exciton transport and energy harvesting from thermal environments
Non-Markovian effects in the evolution of open quantum systems have recently
attracted widespread interest, particularly in the context of assessing the
efficiency of energy and charge transfer in nanoscale biomolecular networks and
quantum technologies. With the aid of many-body simulation methods, we uncover
and analyse an ultrafast environmental process that causes energy relaxation in
the reduced system to depend explicitly on the phase relation of the initial
state preparation. Remarkably, for particular phases and system parameters, the
net energy flow is uphill, transiently violating the principle of detailed
balance, and implying that energy is spontaneously taken up from the
environment. A theoretical analysis reveals that non-secular contributions,
significant only within the environmental correlation time, underlie this
effect. This suggests that environmental energy harvesting will be observable
across a wide range of coupled quantum systems.Comment: 5 + 4 pages, 3 + 2 figures. Comments welcom
Dynamics of an inhomogeneous quantum phase transition
We argue that in a second order quantum phase transition driven by an
inhomogeneous quench density of quasiparticle excitations is suppressed when
velocity at which a critical point propagates across a system falls below a
threshold velocity equal to the Kibble-Zurek correlation length times the
energy gap at freeze-out divided by . This general prediction is
supported by an analytic solution in the quantum Ising chain. Our results
suggest, in particular, that adiabatic quantum computers can be made more
adiabatic when operated in an "inhomogeneous" way.Comment: 7 pages; version to appear in a special issue of New J. Phy
Homogenization of the one-dimensional wave equation
We present a method for two-scale model derivation of the periodic
homogenization of the one-dimensional wave equation in a bounded domain. It
allows for analyzing the oscillations occurring on both microscopic and
macroscopic scales. The novelty reported here is on the asymptotic behavior of
high frequency waves and especially on the boundary conditions of the
homogenized equation. Numerical simulations are reported
Quantification of aircraft trajectory prediction uncertainty using polynomial chaos expansions
A novel approach to quantify the uncertainty associated with any aircraft trajectory prediction based on the application of the Polynomial Chaos (PC) theory is presented. The proposed method relies on univariate polynomial descriptions of the uncertainty sources affecting the trajectory prediction process. Those descriptions are used to build the multivariate polynomial expansions that represent the variability of the aircraft state variables along the predicted trajectory. A case study compares the results obtained by a classical Monte Carlo approach with those generated by applying the so-called arbitrary Polynomial Chaos Expansions (aPCE). The results provided herein lead to conclude that this new methodology can be used to accurately quantify trajectory prediction uncertainty with a very low computational effort, enabling the capability of computing the uncertainty of the individual trajectories of a traffic sample of thousands flights within very short time intervals
Line Shape Broadening in Surface Diffusion of Interacting Adsorbates with Quasielastic He Atom Scattering
The experimental line shape broadening observed in adsorbate diffusion on
metal surfaces with increasing coverage is usually related to the nature of the
adsorbate-adsorbate interaction. Here we show that this broadening can also be
understood in terms of a fully stochastic model just considering two noise
sources: (i) a Gaussian white noise accounting for the surface friction, and
(ii) a shot noise replacing the physical adsorbate-adsorbate interaction
potential. Furthermore, contrary to what could be expected, for relatively weak
adsorbate-substrate interactions the opposite effect is predicted: line shapes
get narrower with increasing coverage.Comment: 4 pages, 2 figures (slightly revised version
Dispersion cancellation and quantum eraser experiments analyzed in the Wigner function formalism
We extend the Wigner function formalism for parametric down-conversion experiments presented in a previous paper [Phys. Rev. A 55 3879 (1997)] to experiments involving propagation through a dispersive medium [Steinberg et al., Phys. Rev. A 45, 6659 (1992)], and polarization [Kwiat et al., Phys. Rev. A 45, 7729 (1992)]
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