481 research outputs found
Decoherence by a spin thermal bath: Role of the spin-spin interactions and initial state of the bath
We study the decoherence of two coupled spins that interact with a spin-bath
environment. It is shown that the connectivity and the coupling strength
between the spins in the environment are of crucial importance for the
decoherence of the central system. For the anisotropic spin-bath, changing the
connectivity or coupling strenghts changes the decoherence of the central
system from Gaussian to exponential decay law. The initial state of the
environment is shown to affect the decoherence process in a qualitatively
significant manner.Comment: submitted to PR
Computer simulation of Wheeler's delayed choice experiment with photons
We present a computer simulation model of Wheeler's delayed choice experiment
that is a one-to-one copy of an experiment reported recently (V. Jacques {\sl
et al.}, Science 315, 966 (2007)). The model is solely based on experimental
facts, satisfies Einstein's criterion of local causality and does not rely on
any concept of quantum theory. Nevertheless, the simulation model reproduces
the averages as obtained from the quantum theoretical description of Wheeler's
delayed choice experiment. Our results prove that it is possible to give a
particle-only description of Wheeler's delayed choice experiment which
reproduces the averages calculated from quantum theory and which does not defy
common sense.Comment: Europhysics Letters (in press
No influence of one right-sided prefrontal HF-rTMS session on alcohol craving in recently detoxified alcohol-dependent patients: results of a naturalistic study
HF-rTMS treatment decreases psychomotor retardation in medication-resistant melancholic depression
A
Corpuscular model of two-beam interference and double-slit experiments with single photons
We introduce an event-based corpuscular simulation model that reproduces the
wave mechanical results of single-photon double slit and two-beam interference
experiments and (of a one-to-one copy of an experimental realization) of a
single-photon interference experiment with a Fresnel biprism. The simulation
comprises models that capture the essential features of the apparatuses used in
the experiment, including the single-photon detectors recording individual
detector clicks. We demonstrate that incorporating in the detector model,
simple and minimalistic processes mimicking the memory and threshold behavior
of single-photon detectors is sufficient to produce multipath interference
patterns. These multipath interference patterns are built up by individual
particles taking one single path to the detector where they arrive one-by-one.
The particles in our model are not corpuscular in the standard, classical
physics sense in that they are information carriers that exchange information
with the apparatuses of the experimental set-up. The interference pattern is
the final, collective outcome of the information exchanges of many particles
with these apparatuses. The interference patterns are produced without making
reference to the solution of a wave equation and without introducing signalling
or non-local interactions between the particles or between different detection
points on the detector screen.Comment: Accepted for publication in J. Phys. Soc. Jpn
Classical and Quantum Annealing in the Median of Three Satisfiability
We determine the classical and quantum complexities of a specific ensemble of
three-satisfiability problems with a unique satisfying assignment for up to
N=100 and N=80 variables, respectively. In the classical limit we employ
generalized ensemble techniques and measure the time that a Markovian Monte
Carlo process spends in searching classical ground states. In the quantum limit
we determine the maximum finite correlation length along a quantum adiabatic
trajectory determined by the linear sweep of the adiabatic control parameter in
the Hamiltonian composed of the problem Hamiltonian and the constant transverse
field Hamiltonian. In the median of our ensemble both complexities diverge
exponentially with the number of variables. Hence, standard, conventional
adiabatic quantum computation fails to reduce the computational complexity to
polynomial. Moreover, the growth-rate constant in the quantum limit is 3.8
times as large as the one in the classical limit, making classical fluctuations
more beneficial than quantum fluctuations in ground-state searches
Corpuscular Event-by-Event Simulation of Quantum Optics Experiments: Application to a Quantum-Controlled Delayed-Choice Experiment
A corpuscular simulation model of optical phenomena that does not require the
knowledge of the solution of a wave equation of the whole system and reproduces
the results of Maxwell's theory by generating detection events one-by-one is
discussed. The event-based corpuscular model gives a unified description of
multiple-beam fringes of a plane parallel plate and single-photon Mach-Zehnder
interferometer, Wheeler's delayed choice, photon tunneling, quantum eraser,
two-beam interference, Einstein-Podolsky-Rosen-Bohm and Hanbury Brown-Twiss
experiments. The approach is illustrated by application to a recent proposal
for a quantum-controlled delayed choice experiment, demonstrating that also
this thought experiment can be understood in terms of particle processes only.Comment: Invited paper presented at FQMT11. Accepted for publication in
Physica Scripta 27 June 201
Structurally Tractable Uncertain Data
Many data management applications must deal with data which is uncertain,
incomplete, or noisy. However, on existing uncertain data representations, we
cannot tractably perform the important query evaluation tasks of determining
query possibility, certainty, or probability: these problems are hard on
arbitrary uncertain input instances. We thus ask whether we could restrict the
structure of uncertain data so as to guarantee the tractability of exact query
evaluation. We present our tractability results for tree and tree-like
uncertain data, and a vision for probabilistic rule reasoning. We also study
uncertainty about order, proposing a suitable representation, and study
uncertain data conditioned by additional observations.Comment: 11 pages, 1 figure, 1 table. To appear in SIGMOD/PODS PhD Symposium
201
Long-lived memory for electronic spin in a quantum dot: Numerical analysis
Techniques for coherent control of electron spin-nuclear spin interactions in
quantum dots can be directly applied in spintronics and in quantum information
processing. In this work we study numerically the interaction of electron and
nuclear spins in the context of storing the spin-state of an electron in a
collective state of nuclear spins. We take into account the errors inherent in
a realistic system: the incomplete polarization of the bath of nuclear spins
and the different hyperfine interactions between the electron and individual
nuclei in the quantum dot. Although these imperfections deteriorate the
fidelity of the quantum information retrieval, we find reasonable fidelities
are achievable for modest bath polarizations.Comment: RevTex, 10 pages, 9 EPS figure
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