1,056 research outputs found
PCN46 ECONOMIC EVALUATION OF ONCOTYPE DX® TO TARGET CHEMOTHERAPY USE IN LYMPH-NODE–NEGATIVE, OESTROGENRECEPTOR–POSITIVE, EARLY-STAGE BREAST CANCER IN IRELAND
Normalization of Collisional Decoherence: Squaring the Delta Function, and an Independent Cross-Check
We show that when the Hornberger--Sipe calculation of collisional decoherence
is carried out with the squared delta function a delta of energy instead of a
delta of the absolute value of momentum, following a method introduced by
Di\'osi, the corrected formula for the decoherence rate is simply obtained. The
results of Hornberger and Sipe and of Di\'osi are shown to be in agreement. As
an independent cross-check, we calculate the mean squared coordinate diffusion
of a hard sphere implied by the corrected decoherence master equation, and show
that it agrees precisely with the same quantity as calculated by a classical
Brownian motion analysis.Comment: Tex: 14 pages 7/30/06: revisions to introduction, and references
added 9/29/06: further minor revisions and references adde
Decoherence in a Talbot Lau interferometer: the influence of molecular scattering
We study the interference of C70 fullerenes in a Talbot-Lau interferometer
with a large separation between the diffraction gratings. This permits the
observation of recurrences of the interference contrast both as a function of
the de Broglie wavelength and in dependence of the interaction with background
gases. We observe an exponential decrease of the fringe visibility with
increasing background pressure and find good quantitative agreement with the
predictions of decoherence theory. From this we extrapolate the limits of
matter wave interferometry and conclude that the influence of collisional
decoherence may be well under control in future experiments with proteins and
even larger objects.Comment: 8 pages, 5 figure
Emergence of pointer states in a non-perturbative environment
We show that the pointer basis distinguished by collisional decoherence
consists of exponentially localized, solitonic wave packets. Based on the
orthogonal unraveling of the quantum master equation, we characterize their
formation and dynamics, and we demonstrate that the statistical weights arising
from an initial superposition state are given by the required projection. Since
the spatial width of the pointer states can be obtained by accounting for the
gas environment in a microscopically realistic fashion, one may thus calculate
the coherence length of a strongly interacting gas.Comment: 8 pages, 1 figure; corresponds to published versio
A Monte Carlo Method for Modeling Thermal Damping: Beyond the Brownian-Motion Master Equation
The "standard" Brownian motion master equation, used to describe thermal
damping, is not completely positive, and does not admit a Monte Carlo method,
important in numerical simulations. To eliminate both these problems one must
add a term that generates additional position diffusion. He we show that one
can obtain a completely positive simple quantum Brownian motion, efficiently
solvable, without any extra diffusion. This is achieved by using a stochastic
Schroedinger equation (SSE), closely analogous to Langevin's equation, that has
no equivalent Markovian master equation. Considering a specific example, we
show that this SSE is sensitive to nonlinearities in situations in which the
master equation is not, and may therefore be a better model of damping for
nonlinear systems.Comment: 6 pages, revtex4. v2: numerical results for a nonlinear syste
Macroscopicity of Mechanical Quantum Superposition States
We propose an experimentally accessible, objective measure for the
macroscopicity of superposition states in mechanical quantum systems. Based on
the observable consequences of a minimal, macrorealist extension of quantum
mechanics, it allows one to quantify the degree of macroscopicity achieved in
different experiments.Comment: 11 pages, 2 figures. v2: Corresponds to the published version, except
for a different numbering of the references. The published "Supplemental
Material" is included as an appendi
The wave nature of biomolecules and fluorofullerenes
We demonstrate quantum interference for tetraphenylporphyrin, the first
biomolecule exhibiting wave nature, and for the fluorofullerene C60F48 using a
near-field Talbot-Lau interferometer. For the porphyrins, which are
distinguished by their low symmetry and their abundant occurence in organic
systems, we find the theoretically expected maximal interference contrast and
its expected dependence on the de Broglie wavelength. For C60F48 the observed
fringe visibility is below the expected value, but the high contrast still
provides good evidence for the quantum character of the observed fringe
pattern. The fluorofullerenes therefore set the new mark in complexity and mass
(1632 amu) for de Broglie wave experiments, exceeding the previous mass record
by a factor of two.Comment: 5 pages, 4 figure
Concept of an ionizing time-domain matter-wave interferometer
We discuss the concept of an all-optical and ionizing matter-wave
interferometer in the time domain. The proposed setup aims at testing the wave
nature of highly massive clusters and molecules, and it will enable new
precision experiments with a broad class of atoms, using the same laser system.
The propagating particles are illuminated by three pulses of a standing
ultraviolet laser beam, which detaches an electron via efficient single
photon-absorption. Optical gratings may have periods as small as 80 nm, leading
to wide diffraction angles for cold atoms and to compact setups even for very
massive clusters. Accounting for the coherent and the incoherent parts of the
particle-light interaction, we show that the combined effect of phase and
amplitude modulation of the matter waves gives rise to a Talbot-Lau-like
interference effect with a characteristic dependence on the pulse delay time.Comment: 25 pages, 5 figure
Spatial Degrees of Freedom in Everett Quantum Mechanics
Stapp claims that, when spatial degrees of freedom are taken into account,
Everett quantum mechanics is ambiguous due to a "core basis problem." To
examine an aspect of this claim I generalize the ideal measurement model to
include translational degrees of freedom for both the measured system and the
measuring apparatus. Analysis of this generalized model using the Everett
interpretation in the Heisenberg picture shows that it makes unambiguous
predictions for the possible results of measurements and their respective
probabilities. The presence of translational degrees of freedom for the
measuring apparatus affects the probabilities of measurement outcomes in the
same way that a mixed state for the measured system would. Examination of a
measurement scenario involving several observers illustrates the consistency of
the model with perceived spatial localization of the measuring apparatus.Comment: 34 pp., no figs. Introduction, discussion revised. Material
tangential to main point remove
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