1,193 research outputs found
Enhanced observability of quantum post-exponential decay using distant detectors
We study the elusive transition from exponential to post-exponential
(algebraic) decay of the probability density of a quantum particle emitted by
an exponentially decaying source, in one dimension. The main finding is that
the probability density at the transition time, and thus its observability,
increases with the distance of the detector from the source, up to a critical
distance beyond which exponential decay is no longer observed. Solvable models
provide explicit expressions for the dependence of the transition on resonance
and observational parameters, facilitating the choice of optimal conditions
A model for single electron decays from a strongly isolated quantum dot
Recent measurements of electron escape from a non-equilibrium charged quantum
dot are interpreted within a 2D separable model. The confining potential is
derived from 3D self-consistent Poisson-Thomas-Fermi calculations. It is found
that the sequence of decay lifetimes provides a sensitive test of the confining
potential and its dependence on electron occupation.Comment: 9 pages, 10 figure
Surface EM waves on 1D Photonic Crystals
We study surface states of 1D photonic crystals using a semiclassical coupled
wave theory. Both TE and TM modes are treated. We derive analytic
approximations that clarify the systematics of the dispersion relations, and
the roles of the various parameters defining the crystal.Comment: 7 pages, 8 figure
Modeling and manufacturability assessment of bistable quantum-dot cells
We have investigated the behavior of bistable cells made up of four quantum
dots and occupied by two electrons, in the presence of realistic confinement
potentials produced by depletion gates on top of a GaAs/AlGaAs heterostructure.
Such a cell represents the basic building block for logic architectures based
on the concept of Quantum Cellular Automata (QCA) and of ground state
computation, which have been proposed as an alternative to traditional
transistor-based logic circuits. We have focused on the robustness of the
operation of such cells with respect to asymmetries deriving from fabrication
tolerances. We have developed a 2-D model for the calculation of the electron
density in a driven cell in response to the polarization state of a driver
cell. Our method is based on the one-shot Configuration-Interaction technique,
adapted from molecular chemistry. From the results of our simulations, we
conclude that an implementation of QCA logic based on simple ``hole-arrays'' is
not feasible, because of the extreme sensitivity to fabrication tolerances. As
an alternative, we propose cells defined by multiple gates, where geometrical
asymmetries can be compensated for by adjusting the bias voltages. Even though
not immediately applicable to the implementation of logic gates and not
suitable for large scale integration, the proposed cell layout should allow an
experimental demonstration of a chain of QCA cells.Comment: 26 pages, Revtex, 13 figures, title and some figures changed and
minor revision
Classical picture of post-exponential decay
Post-exponential decay of the probability density of a quantum particle
leaving a trap can be reproduced accurately, except for interference
oscillations at the transition to the post-exponential regime, by means of an
ensemble of classical particles emitted with constant probability per unit time
and the same half-life as the quantum system. The energy distribution of the
ensemble is chosen to be identical to the quantum distribution, and the
classical point source is located at the scattering length of the corresponding
quantum system. A 1D example is provided to illustrate the general argument
Fast generation of spin-squeezed states in bosonic Josephson junctions
We describe methods for fast production of highly coherent-spin-squeezed
many-body states in bosonic Josephson junctions (BJJs). We start from the known
mapping of the two-site Bose-Hubbard (BH) Hamiltonian to that of a single
effective particle evolving according to a Schr\"odinger-like equation in Fock
space. Since, for repulsive interactions, the effective potential in Fock space
is nearly parabolic, we extend recently derived protocols for shortcuts to
adiabatic evolution in harmonic potentials to the many-body BH Hamiltonian. The
best scaling of the squeezing parameter for large number of atoms N is \xi^2_S
~ 1/N.Comment: Improved and enlarged version, accepted at Phys. Rev.
Influence of morning maternal care on the behavioural responses of 8-week-old Beagle puppies to new environmental and social stimuli
In mammals, maternal care represents a major constituent of the early-life environment and its influence on individual development has been documented in rodents, non-human primates, humans and recently in adult dogs. The quality and quantity of mother-offspring interactions exerts a multilevel regulation upon the physiological, cognitive, and behavioural development of the offspring. For example, in rats variations in maternal behaviour, such as mother-pup body contact and the amount of licking towards pups in the nest during the early days after parturition, influences the endocrine, emotional, and behavioural responses to stress in the offspring. This produces long-term consequences, which may remain into adulthood and can be transmitted to subsequent generations. Literature about maternal care in dogs and its effect on puppy behaviour is still scarce, although the topic is receiving a growing interest. The aim of the present study was to determine the effects of morning maternal care on behavioural responses of puppies to new environmental and social stimuli. In order to achieve this, maternal care (licking, ano-genital licking, nursing and mother-puppy contact) was assessed in eight litters of domestic dogs living in standard rearing conditions during the first three weeks post-partum. Puppies were subjected to two behavioural tests (arena and isolation tests) at 58-60 days of age, and their behavioural responses were video recorded and analysed. Data was analysed using multivariate analyses (PCA, PLS).During the isolation test, a higher level of maternal care was associated with more exploration and a higher latency to emit the first yelp; on the contrary, a lower level of maternal care was associated with increased locomotion, distress vocalisations and destructive behaviours directed at the enclosure.These results, comparable to those reported in laboratory rat models and to some extent to those recently reported in dog literature, highlight the importance of maternal care on the behavioural development of domestic dog puppies
Memory effects induced by initial switching conditions
Initial-switching refers to the way in which the decay of an initially
confined state begins, as the barrier isolating it from the exterior is
relaxed. We study these effects in the context of Longhi's version of the
Fano-Anderson model. Most authors assume the sudden approximation where the
coupling is turned on instantaneously. We consider a finite rise time T, both
numerically and analytically. When the coupling is ramped up linearly over a
switching time T, we show that the asymptotic survival amplitude acquires a
phase T and is modulated by a factor (sin T)/T. Several other results relating
to the solution of the model are obtained. All site amplitudes have the same
decay constant during the exponential decay regime. In the asymptotic regime,
the amplitude and phase of decay oscillations depend on the initial-switching
profile, but the period does not.Comment: 12 pages, 10 figures, accepted by Phys. Rev.
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