95 research outputs found
Quantum scaling laws in the onset of dynamical delocalization
We study the destruction of dynamical localization, experimentally observed
in an atomic realization of the kicked rotor, by a deterministic Hamiltonian
perturbation, with a temporal periodicity incommensurate with the principal
driving. We show that the destruction is gradual, with well defined scaling
laws for the various classical and quantum parameters, in sharp contrast with
predictions based on the analogy with Anderson localization.Comment: 3 pages, revtex
Optimal frequency conversion in the nonlinear stage of modulation instability
We investigate multi-wave mixing associated with the strongly pump depleted
regime of induced modulation instability (MI) in optical fibers. For a complete
transfer of pump power into the sideband modes, we theoretically and
experimentally demonstrate that it is necessary to use a much lower seeding
modulation frequency than the peak MI gain value. Our analysis shows that a
record 95 % of the input pump power is frequency converted into the comb of
sidebands, in good quantitative agreement with analytical predictions based on
the simplest exact breather solution of the nonlinear Schr\"odinger equation
Experimental verification of the Heisenberg uncertainty principle for hot fullerene molecules
The Heisenberg uncertainty principle for material objects is an essential
corner stone of quantum mechanics and clearly visualizes the wave nature of
matter. Here we report a demonstration of the Heisenberg uncertainty principle
for the most massive, complex and hottest single object so far, the fullerene
molecule C70 at a temperature of 900 K. We find a good quantitative agreement
with the theoretical expectation: dx * dp = h, where dx is the width of the
restricting slit, dp is the momentum transfer required to deflect the fullerene
to the first interference minimum and h is Planck's quantum of action.Comment: 4 pages, 4 figure
Delay time and tunneling transient phenomena
Analytic solutions to the time-dependent Schr\"odinger equation for cutoff
wave initial conditions are used to investigate the time evolution of the
transmitted probability density for tunneling. For a broad range of values of
the potential barrier opacity , we find that the probability density
exhibits two evolving structures. One refers to the propagation of a {\it
forerunner} related to a {\it time domain resonance} [Phys. Rev. A {\bf 64},
0121907 (2001)], while the other consists of a semiclassical propagating
wavefront. We find a regime where the {\it forerunners} are absent,
corresponding to positive {\it time delays}, and show that this regime is
characterized by opacities . The critical opacity
is derived from the analytical expression for the {\it delay time}, that
reflects a link between transient effects in tunneling and the {\it delay time}Comment: To be published in Physical Review
Transient tunneling effects of resonance doublets in triple barrier systems
Transient tunneling effects in triple barrier systems are investigated by
considering a time-dependent solution to the Schr\"{o}dinger equation with a
cutoff wave initial condition. We derive a two-level formula for incidence
energies near the first resonance doublet of the system. Based on that
expression we find that the probability density along the internal region of
the potential, is governed by three oscillation frequencies: one of them refers
to the well known Bohr frequency, given in terms of the first and second
resonance energies of the doublet, and the two others, represent a coupling
with the incidence energy . This allows to manipulate the above frequencies
to control the tunneling transient behavior of the probability density in the
short-time regim
On the significance of a recent experiment demonstrating quantum interference in time
I comment on the interpretation of a recent experiment showing quantum
interference in time. It is pointed out that the standard nonrelativistic
quantum theory, used by the authors in their analysis, cannot account for the
results found, and therefore that this experiment has fundamental importance
beyond the technical advances it represents. Some theoretical structures which
consider the time as an observable, and thus could, in principle, have the
required coherence in time, are discussed briefly, and the application of
Floquet theory and the manifestly covariant quantum theory of Stueckelberg are
treated in some detail. In particular, the latter is shown to account for the
results in a simple and consistent way.Comment: 10 pages, plain TeX. Revision for clarity, reference to other
candidate theorie
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