54 research outputs found
Effect of noise and modulation on the reflection of atoms from an evanescent wave
We consider the reflection of cold atoms from a temporally modulated evanescent wave, with laser intensity noise, including stochastic surface adsorption. The stochastic surface adsorption is explicitly modeled by means of quantum trajectories while the effect of noise is modeled using the method of stochastic Hamiltonians. The results show that noise destroys quantum features such as interference and splitting, which is especially rapid for semiclassical states. For small noise, modulation can still produce a splitting of the atomic beam, with added dispersion resulting from heating of atoms. In order to distinguish the quantum features, a classical analysis is also presented
Dissipative nonlinear quantum dynamics in atomic optics
It is proposed that the atomic optical system of an ytterbium atom in a time-dependent optical standing wave be used to experimentally observe quantum nonlinear motion and, in particular, predict the quantum behavior of a system whose classical analog ranges from completely integrable, to near integrable, and finally to globally chaotic motion. We extend previous treatments to include spontaneous emission. From the study of theoretical models of dissipative quantum nonlinear motion, it is known that even small amounts of dissipation can significantly alter the quantum dynamics through the destruction of coherences. In this paper we present some theoretical and numerical results of the effect of spontaneous emission on nonlinear nonintegrable dynamics in atomic optics. When spontaneous emission is included, we show that the nature of the light-atom interaction introduces interesting features not usually investigated in models of dissipative quantum nonlinear dynamics. These include a potential that depends on the atom's internal state, a band structure, and a time-dependent dissipative process
Quantum Zeno effect and parametric resonance in mesoscopic physics
As a realization of the quantum Zeno effect, we consider electron tunneling
between two quantum dots with one of the dots coupled to a quantum point
contact detector. The coupling leads to decoherence and to the suppression of
tunneling. When the detector is driven with an ac voltage, a parametric
resonance occurs which strongly counteracts decoherence. We propose a novel
experiment with which it is possible to observe both the quantum Zeno effect
and the parametric resonance in electric transport.Comment: 4 pages, 2 figure
Quantum signatures of chaos in the dynamics of a trapped ion
We show how a nonlinear chaotic system, the parametrically kicked nonlinear
oscillator, may be realised in the dynamics of a trapped, laser-cooled ion,
interacting with a sequence of standing wave pulses. Unlike the original
optical scheme [G.J.Milburn and C.A.Holmes, Phys. Rev A, 44, p4704, (1991)],
the trapped ion enables strongly quantum dynamics with minimal dissipation.
This should permit an experimental test of one of the quantum signatures of
chaos; irregular collapse and revival dynamics of the average vibrational
energy.Comment: 9 pages, 9 Postscript figures, Revtex, submitted to Phys. Rev.
Decoherence in ion traps due to laser intensity and phase fluctuations
We consider one source of decoherence for a single trapped ion due to
intensity and phase fluctuations in the exciting laser pulses. For simplicity
we assume that the stochastic processes involved are white noise processes,
which enables us to give a simple master equation description of this source of
decoherence. This master equation is averaged over the noise, and is sufficient
to describe the results of experiments that probe the oscillations in the
electronic populations as energy is exchanged between the internal and
electronic motion. Our results are in good qualitative agreement with recent
experiments and predict that the decoherence rate will depend on vibrational
quantum number in different ways depending on which vibrational excitation
sideband is used.Comment: 2 figures, submitted to PR
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
Decoherence in a single trapped ion due to engineered reservoir
The decoherence in trapped ion induced by coupling the ion to the engineered
reservoir is studied in this paper. The engineered reservoir is simulated by
random variations in the trap frequency, and the trapped ion is treated as a
two-level system driven by a far off-resonant plane wave laser field. The
dependence of the decoherence rate on the amplitude of the superposition state
is given.Comment: 4 pages, 2 figure
Quantum slow motion
We investigate the center-of-mass motion of cold atoms in a standing amplitude modulated laser field. We use a simple model to explain the momentum distribution of the atoms after any distinct number of modulation cycles. The atoms starting near a classical phase-space resonance move slower than we would expect classically. We explain this by showing that for a wave packet on the classical resonances we can replace the complicated dynamics in the quantum Liouville equation in phase space by its classical dynamics with a modified potential
Creation of gap solitons in Bose-Einstein condensates
We discuss a method to launch gap soliton-like structures in atomic
Bose-Einstein condensates confined in optical traps. Bright vector solitons
consisting of a superposition of two hyperfine Zeeman sublevels can be created
for both attractive and repulsive interactions between the atoms. Their
formation relies on the dynamics of the atomic internal ground states in two
far-off resonant counterpropagating sigma^+ sigma^- polarized laser beams which
form the optical trap. Numerical simulations show that these solitons can be
prepared from a one-component state provided with an initial velocity.Comment: 6 pages, 3 figure
Sensitivity to measurement perturbation of single atom dynamics in cavity QED
We consider continuous observation of the nonlinear dynamics of single atom
trapped in an optical cavity by a standing wave with intensity modulation. The
motion of the atom changes the phase of the field which is then monitored by
homodyne detection of the output field. We show that the conditional Hilbert
space dynamics of this system, subject to measurement induced perturbations,
depends strongly on whether the corresponding classical dynamics is regular or
chaotic. If the classical dynamics is chaotic the distribution of conditional
Hilbert space vectors corresponding to different observation records tends to
be orthogonal. This is a characteristic feature of hypersensitivity to
perturbation for quantum chaotic systems.Comment: 11 pages, 6 figure
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