2,240 research outputs found
Quantum Kicked Dynamics and Classical Diffusion
We consider the quantum counterpart of the kicked harmonic oscillator showing
that it undergoes the effect of delocalization in momentum when the classical
diffusional threshold is obeyed.
For this case the ratio between the oscillator frequency and the frequency of
the kick is a rational number, strictly in analogy with the classical case that
does not obey the Kolmogorov-Arnold-Moser theorem as the unperturbed motion is
degenerate.
A tight-binding formulation is derived showing that there is not
delocalization in momentum for irrational ratio of the above frequencies. In
this way, it is straightforwardly seen that the behavior of the quantum kicked
rotator is strictly similar to the one of the quantum kicked harmonic
oscillator, although the former, in the classical limit, obeys the
Kolmogorov-Arnold-Moser theorem.Comment: 9 pages, LaTeX. Comments are welcom
Non-monotonic diffusion rates in atom-optics L\'{e}vy kicked rotor
The dynamics of chaotic Hamiltonian systems such as the kicked rotor
continues to guide our understanding of transport and localization processes.
The localized states of the quantum kicked rotor decay due to decoherence
effects if subjected to stationary noise. The associated quantum diffusion
increases monotonically as a function of a parameter characterising the noise
distribution. In this work, for the Levy kicked atom-optics rotor, it is
experimentally shown that by tuning a parameter characterizing the Levy
distribution, quantum diffusion displays non-monotonic behaviour. The
parameters for optimal diffusion rates are analytically obtained and they
reveal a good agreement with the cold atom experiments and numerics. The
non-monotonicity is shown to be a quantum effect that vanishes in the classical
limit.Comment: 5 pages, revte
Atoms in double-delta-kicked periodic potentials: Chaos with long-range correlations
We report an experimental and theoretical study of the dynamics of cold atoms subjected to pairs of closely spaced pulses in an optical lattice. For all previously studied delta-kicked systems, chaotic classical dynamics shows diffusion with short-time (2- or 3-kick) correlations; here, chaotic diffusion combines with new types of long-ranged global correlations, between all kick pairs, which control transport through trapping regions in phase space. Correlations are studied in the classical regime, but the diffusive behavior observed in experiment depends on the quantum dynamical localization
Control of Dynamical Localization
Control over the quantum dynamics of chaotic kicked rotor systems is
demonstrated. Specifically, control over a number of quantum coherent phenomena
is achieved by a simple modification of the kicking field. These include the
enhancement of the dynamical localization length, the introduction of classical
anomalous diffusion assisted control for systems far from the semiclassical
regime, and the observation of a variety of strongly nonexponential lineshapes
for dynamical localization. The results provide excellent examples of
controlled quantum dynamics in a system that is classically chaotic and offer
new opportunities to explore quantum fluctuations and correlations in quantum
chaos.Comment: 9 pages, 7 figures, to appear in Physical Review
Classical and quantum dynamics of the n-dimensional kicked rotator
The classical and quantum dynamics for an n-dimensional generalization of the
kicked planar (n=1) rotator in an additional effective centrifugal potential.
Therefore, typical phenomena like the diffusion in classical phase space are
similar to that of the one-dimensional model. For the quantum dynamics such a
result is not expected as in this case the evolution does depend in a very
complicated way on the number n of degrees of freedom. In the limit n -->
infinity we find the free undistrubed quantum motion. For finite values of n
(1<=n<=26) we study numerically the quantum dynamics. Here, we always find
localization independent of the actual number of degrees of freedom.Comment: uuencoded gzipped postscript file, Problem in postscript file
resolved. For uncompressed postscript file see
http://faupt101.physik.uni-erlangen.de/junker/papers95.ht
Sigma models for quantum chaotic dynamics
We review the construction of the supersymmetric sigma model for unitary
maps, using the color- flavor transformation. We then illustrate applications
by three case studies in quantum chaos. In two of these cases, general Floquet
maps and quantum graphs, we show that universal spectral fluctuations arise
provided the pertinent classical dynamics are fully chaotic (ergodic and with
decay rates sufficiently gapped away from zero). In the third case, the kicked
rotor, we show how the existence of arbitrarily long-lived modes of excitation
(diffusion) precludes universal fluctuations and entails quantum localization
Diffusion Resonances in Action Space for an Atom Optics Kicked Rotor with Decoherence
We numerically investigate momentum diffusion rates for the pulse kicked
rotor across the quantum to classical transition as the dynamics are made more
macroscopic by increasing the total system action. For initial and late time
rates we observe an enhanced diffusion peak which shifts and scales with
changing kick strength, and we also observe distinctive peaks around quantum
resonances. Our investigations take place in the context of a system of
ultracold atoms which is coupled to its environment via spontaneous emission
decoherence, and the effects should be realisable in ongoing experiments.Comment: 4 Pages, RevTeX 4, 5 Figures. Updated Figures, Minor Changes to text,
Corrected Reference
Quantum to classical transition in a system with a mixed classical dynamics
We study how decoherence rules the quantum-classical transition of the Kicked
Harmonic Oscillator (KHO). When the amplitude of the kick is changed the system
presents a classical dynamics that range from regular to a strong chaotic
behavior. We show that for regular and mixed classical dynamics, and in the
presence of noise, the distance between the classical and the quantum phase
space distributions is proportional to a single parameter which relates the effective Planck constant
, the kick amplitude and the diffusion constant . This
is valid when , a case that is always attainable in the semiclassical
regime independently of the value of the strength of noise given by . Our
results extend a recent study performed in the chaotic regime.Comment: 10 pages, 7 figure
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