1,151 research outputs found
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.
Quantum Chaotic System in the Generalized Husimi Representation - Comment
In a recent paper [K. Życzkowski, Phys. Rev. A 35, 3546 (1987)] the generalized Husimi distribution was used to investigate the quantum kicked rotator. It was shown that in the classically chaotic region the Husimi distribution displayed a ‘‘rippled irregular shape.’’ It was suggested that such behavior could be considered as a qualitative criterion for quantum chaos. In this Comment it is suggested that such behavior is not necessarily associated with quantum chaos. The rippled irregular features may be due to quantum interference effects between superposed states
Kerr nonlinearities and nonclassical states with superconducting qubits and nanomechanical resonators
We propose the use of a superconducting charge qubit capacitively coupled to
two resonant nanomechanical resonators to generate Yurke-Stoler states, i.e.
quantum superpositions of pairs of distinguishable coherent states 180
out of phase with each other. This is achieved by effectively implementing Kerr
nonlinearities induced through application of a strong external driving field
in one of the resonators. A simple study of the effect of dissipation on our
scheme is also presented, and lower bounds of fidelity and purity of the
generated state are calculated. Our procedure to implement a Kerr nonlinearity
in this system may be used for high precision measurements in nanomechanical
resonators.Comment: 5 pages, 2 figures, fixed typo
Quantum Dynamics of Three Coupled Atomic Bose-Einstein Condensates
The simplest model of three coupled Bose-Einstein Condensates (BEC) is
investigated using a group theoretical method. The stationary solutions are
determined using the SU(3) group under the mean field approximation. This
semiclassical analysis using the system symmetries shows a transition in the
dynamics of the system from self trapping to delocalization at a critical value
for the coupling between the condensates. The global dynamics are investigated
by examination of the stable points and our analysis shows the structure of the
stable points depends on the ratio of the condensate coupling to the
particle-particle interaction, undergoes bifurcations as this ratio is varied.
This semiclassical model is compared to a full quantum treatment, which also
displays the dynamical transition. The quantum case has collapse and revival
sequences superposed on the semiclassical dynamics reflecting the underlying
discreteness of the spectrum. Non-zero circular current states are also
demonstrated as one of the higher dimensional effects displayed in this system.Comment: Accepted to PR
The dynamics of a strongly driven two component Bose-Einstein Condensate
We consider a two component Bose-Einstein condensate in two spatially
localized modes of a double well potential, with periodic modulation of the
tunnel coupling between the two modes. We treat the driven quantum field using
a two mode expansion and define the quantum dynamics in terms of the Floquet
Operator for the time periodic Hamiltonian of the system. It has been shown
that the corresponding semiclassical mean-field dynamics can exhibit regions of
regular and chaotic motion. We show here that the quantum dynamics can exhibit
dynamical tunneling between regions of regular motion, centered on fixed points
(resonances) of the semiclassical dynamics
Gravitational Laser Back-Scattering
A possible way of producing gravitons in the laboratory is investigated. We
evaluate the cross section electron + photon electron + graviton
in the framework of linearized gravitation, and analyse this reaction
considering the photon coming either from a laser beam or from a Compton
back-scattering process.Comment: 11 pages, 2 figures (available upon request), RevTeX, IFT-P.03/9
Decoherence-based exploration of d-dimensional one-way quantum computation
We study the effects of amplitude and phase damping decoherence in
d-dimensional one-way quantum computation (QC). Our investigation shows how
information transfer and entangling gate simulations are affected for d>=2. To
understand motivations for extending the one-way model to higher dimensions, we
describe how d-dimensional qudit cluster states deteriorate under environmental
noise. In order to protect quantum information from the environment we consider
the encoding of logical qubits into physical qudits and compare entangled pairs
of linear qubit-cluster states with single qudit clusters of equal length and
total dimension. Our study shows a significant reduction in the performance of
one-way QC for d>2 in the presence of Markovian type decoherence models.Comment: 8 pages, 11 figures, RevTeX
Fast simulation of a quantum phase transition in an ion-trap realisable unitary map
We demonstrate a method of exploring the quantum critical point of the Ising
universality class using unitary maps that have recently been demonstrated in
ion trap quantum gates. We reverse the idea with which Feynman conceived
quantum computing, and ask whether a realisable simulation corresponds to a
physical system. We proceed to show that a specific simulation (a unitary map)
is physically equivalent to a Hamiltonian that belongs to the same universality
class as the transverse Ising Hamiltonian. We present experimental signatures,
and numerical simulation for these in the six-qubit case.Comment: 12 pages, 6 figure
Self-trapping mechanisms in the dynamics of three coupled Bose-Einstein condensates
We formulate the dynamics of three coupled Bose-Einstein condensates within a
semiclassical scenario based on the standard boson coherent states. We compare
such a picture with that of Ref. 1 and show how our approach entails a simple
formulation of the dimeric regime therein studied. This allows to recognize the
parameters that govern the bifurcation mechanism causing self-trapping, and
paves the way to the construction of analytic solutions. We present the results
of a numerical simulation showing how the three-well dynamics has, in general,
a cahotic behavior.Comment: 4 pages, 5 figure
Lorentz invariant intrinsic decoherence
Quantum decoherence can arise due to classical fluctuations in the parameters
which define the dynamics of the system. In this case decoherence, and
complementary noise, is manifest when data from repeated measurement trials are
combined. Recently a number of authors have suggested that fluctuations in the
space-time metric arising from quantum gravity effects would correspond to a
source of intrinsic noise, which would necessarily be accompanied by intrinsic
decoherence. This work extends a previous heuristic modification of
Schr\"{o}dinger dynamics based on discrete time intervals with an intrinsic
uncertainty. The extension uses unital semigroup representations of space and
time translations rather than the more usual unitary representation, and does
the least violence to physically important invariance principles. Physical
consequences include a modification of the uncertainty principle and a
modification of field dispersion relations, in a way consistent with other
modifications suggested by quantum gravity and string theory .Comment: This paper generalises an earlier model published as Phys. Rev. A
vol44, 5401 (1991
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