504 research outputs found
Massive Parallel Quantum Computer Simulator
We describe portable software to simulate universal quantum computers on
massive parallel computers. We illustrate the use of the simulation software by
running various quantum algorithms on different computer architectures, such as
a IBM BlueGene/L, a IBM Regatta p690+, a Hitachi SR11000/J1, a Cray X1E, a SGI
Altix 3700 and clusters of PCs running Windows XP. We study the performance of
the software by simulating quantum computers containing up to 36 qubits, using
up to 4096 processors and up to 1 TB of memory. Our results demonstrate that
the simulator exhibits nearly ideal scaling as a function of the number of
processors and suggest that the simulation software described in this paper may
also serve as benchmark for testing high-end parallel computers.Comment: To appear in Comp. Phys. Com
Correlation between the reliability of HEMT devices and that of a combined oscillator-amplifier
We evaluate an oscillator-amplifier MMIC submitted to high-temperature operating life time tests. To relate adequately these results with individual components’ results, it is important to realise that failure mechanisms in non-linear MMICs are governed by the maximally instantaneous voltages/currents and hence that comparisons should be conducted at equal instantaneous conditions
Proposal for an interference experiment to test the applicability of quantum theory to event-based processes
We analyze a single-particle Mach-Zehnder interferometer experiment in which
the path length of one arm may change (randomly or systematically) according to
the value of an external two-valued variable , for each passage of a
particle through the interferometer. Quantum theory predicts an interference
pattern that is independent of the sequence of the values of . On the other
hand, corpuscular models that reproduce the results of quantum optics
experiments carried out up to this date show a reduced visibility and a shift
of the interference pattern depending on the details of the sequence of the
values of . The proposed experiment will show that: (1) it can be described
by quantum theory, and thus not by the current corpuscular models, or (2) it
cannot be described by quantum theory but can be described by the corpuscular
models or variations thereof, or (3) it can neither be described by quantum
theory nor by corpuscular models. Therefore, the proposed experiment can be
used to determine to what extent quantum theory provides a description of
observed events beyond the usual statistical level.Comment: Accepted for publication in J. Phys. Soc. Jp
Continuous-Time Quantum Monte Carlo Algorithm for the Lattice Polaron
An efficient continuous-time path-integral Quantum Monte Carlo algorithm for
the lattice polaron is presented. It is based on Feynman's integration of
phonons and subsequent simulation of the resulting single-particle
self-interacting system. The method is free from the finite-size and
finite-time-step errors and works in any dimensionality and for any range of
electron-phonon interaction. The ground-state energy and effective mass of the
polaron are calculated for several models. The polaron spectrum can be measured
directly by Monte Carlo, which is of general interest.Comment: 5 pages, 4 figures, published versio
Manual for COMMUTE, a FORTRAN Program for Symbolic Evaluation of Commutators and Correlation Functions
COMMUTE is a FORTRAN program that can be used for the symbolic evaluation of equations of motion of operators or correlation functions. It can use symmetry operations to reduce the final number of terms and in some specific cases, it expresses correlation functions in terms of known functions. It is extremely useful for the calculation of the coefficients in the short-time expansion of a correlation function
Decoherence by a chaotic many-spin bath
We numerically investigate decoherence of a two-spin system (central system)
by a bath of many spins 1/2. By carefully adjusting parameters, the dynamical
regime of the bath has been varied from quantum chaos to regular, while all
other dynamical characteristics have been kept practically intact. We
explicitly demonstrate that for a many-body quantum bath, the onset of quantum
chaos leads to significantly faster and stronger decoherence compared to an
equivalent non-chaotic bath. Moreover, the non-diagonal elements of the
system's density matrix decay differently for chaotic and non-chaotic baths.
Therefore, knowledge of the basic parameters of the bath (strength of the
system-bath interaction, bath's spectral density of states) is not always
sufficient, and much finer details of the bath's dynamics can strongly affect
the decoherence process.Comment: 4 pages, RevTeX, 5 eps figure
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
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