797 research outputs found
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
Fast Algorithm for Finding the Eigenvalue Distribution of Very Large Matrices
A theoretical analysis is given of the equation of motion method, due to
Alben et al., to compute the eigenvalue distribution (density of states) of
very large matrices. The salient feature of this method is that for matrices of
the kind encountered in quantum physics the memory and CPU requirements of this
method scale linearly with the dimension of the matrix. We derive a rigorous
estimate of the statistical error, supporting earlier observations that the
computational efficiency of this approach increases with matrix size. We use
this method and an imaginary-time version of it to compute the energy and the
specific heat of three different, exactly solvable, spin-1/2 models and compare
with the exact results to study the dependence of the statistical errors on
sample and matrix size.Comment: 24 pages, 24 figure
Quantum Monte Carlo Method for Attractive Coulomb Potentials
Starting from an exact lower bound on the imaginary-time propagator, we
present a Path-Integral Quantum Monte Carlo method that can handle singular
attractive potentials. We illustrate the basic ideas of this Quantum Monte
Carlo algorithm by simulating the ground state of hydrogen and helium.Comment: 7 pages, 3 table
Finite-temperature charge transport in the one-dimensional Hubbard model
We study the charge conductivity of the one-dimensional repulsive Hubbard
model at finite temperature using the method of dynamical quantum typicality,
focusing at half filling. This numerical approach allows us to obtain current
autocorrelation functions from systems with as many as 18 sites, way beyond the
range of standard exact diagonalization. Our data clearly suggest that the
charge Drude weight vanishes with a power law as a function of system size. The
low-frequency dependence of the conductivity is consistent with a finite dc
value and thus with diffusion, despite large finite-size effects. Furthermore,
we consider the mass-imbalanced Hubbard model for which the charge Drude weight
decays exponentially with system size, as expected for a non-integrable model.
We analyze the conductivity and diffusion constant as a function of the mass
imbalance and we observe that the conductivity of the lighter component
decreases exponentially fast with the mass-imbalance ratio. While in the
extreme limit of immobile heavy particles, the Falicov-Kimball model, there is
an effective Anderson-localization mechanism leading to a vanishing
conductivity of the lighter species, we resolve finite conductivities for an
inverse mass ratio of .Comment: 13 pages, 11 figure
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
Real-time broadening of non-equilibrium density profiles and the role of the specific initial-state realization
The real-time broadening of density profiles starting from non-equilibrium
states is at the center of transport in condensed-matter systems and dynamics
in ultracold atomic gases. Initial profiles close to equilibrium are expected
to evolve according to linear response, e.g., as given by the current
correlator evaluated exactly at equilibrium. Significantly off equilibrium,
linear response is expected to break down and even a description in terms of
canonical ensembles is questionable. We unveil that single pure states with
density profiles of maximum amplitude yield a broadening in perfect agreement
with linear response, if the structure of these states involves randomness in
terms of decoherent off-diagonal density-matrix elements. While these states
allow for spin diffusion in the XXZ spin-1/2 chain at large exchange
anisotropies, coherences yield entirely different behavior.Comment: 7 pages, 7 figures, accepted for publication in Phys. Rev.
Eigenstate Thermalization Hypothesis and Quantum Jarzynski Relation for Pure Initial States
Since the first suggestion of the Jarzynski equality many derivations of this
equality have been presented in both, the classical and the quantum context.
While the approaches and settings greatly differ from one to another, they all
appear to rely on the initial state being a thermal Gibbs state. Here, we
present an investigation of work distributions in driven isolated quantum
systems, starting off from pure states that are close to energy eigenstates of
the initial Hamiltonian. We find that, for the nonintegrable system in quest,
the Jarzynski equality is fulfilled to good accuracy.Comment: 9 pages, 7 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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