34 research outputs found
Numerical analysis of a spontaneous collapse model for a two-level system
We study a spontaneous collapse model for a two-level (spin) system, in which
the Hamiltonian and the stochastic terms do not commute. The numerical solution
of the equations of motions allows to give precise estimates on the regime at
which the collapse of the state vector occurs, the reduction and delocalization
times, and the reduction probabilities; it also allows to quantify the effect
that an Hamiltonian which does not commute with the reducing terms has on the
collapse mechanism. We also give a clear picture of the transition from the
"microscopic" regime (when the noise terms are weak and the Hamiltonian
prevents the state vector to collapse) to the "macroscopic" regime (when the
noise terms are dominant and the collapse becomes effective for very long
times). Finally, we clarify the distinction between decoherence and collapse.Comment: 7 pages, RevTeX. Significative improvements made. To appear on Phys.
Rev.
Experimental Test of Relativistic Quantum State Collapse with Moving Reference Frames
An experimental test of relativistic wave-packet collapse is presented. The
tested model assumes that the collapse takes place in the reference frame
determined by the massive measuring detectors. Entangled photons are measured
at 10 km distance within a time interval of less than 5 ps. The two apparatuses
are in relative motion so that both detectors, each in its own inertial
reference frame, are first to perform the measurement. The data always
reproduces the quantum correlations and thus rule out a class of collapse
models. The results also set a lower bound on the "speed of quantum
information" to 0.66 x 10^7 and 1.5 x 10^4 times the speed of light in the
Geneva and the background radiation reference frames, respectively. The very
difficult and deep question of where the collapse takes place - if it takes
place at all - is considered in a concrete experimental context.Comment: 4 pages + 2 ps figure
On Uniqueness of the Jump Process in Quantum Measurement Theory
We prove that, contrary to the standard quantum theory of continuous
observation, in the formalism of Event Enhanced Quantum Theory the stochastic
process generating individual sample histories of pairs (observed quantum
system, observing classical apparatus) is unique. This result gives a rigorous
basis to the previous heuristic argument of Blanchard and Jadczyk. Possible
implications of this result are discussed.Comment: 31 pages, LaTeX, article; e-mail contact [email protected]
Quantum correlations versus Multisimultaneity: an experimental test
Multisimultaneity is a causal model of relativistic quantum physics which
assigns a real time ordering to any set of events, much in the spirit of the
pilot-wave picture. Contrary to standard quantum mechanics, it predicts a
disappearance of the correlations in a Bell-type experiment when both analysers
are in relative motion such that, each one in its own inertial reference frame,
is first to select the output of the photons. We tested this prediction using
acousto-optic modulators as moving beam-splitters and interferometers separated
by 55 m. We didn't observe any disappearance of the correlations, thus refuting
Multisimultaneity.Comment: 4 pages, 3 figures, RevTex 4 versio
On Quantum Jumps, Events and Spontaneous Localization Models
We propose a definite meaning to the concepts of "experiment", "measurement"
and "event" in the event-enhanced formalism of quantum theory. A minimal
piecewise deterministic process is given that can be used for a computer
simulation of real time series of experiments on single quantum objects. As an
example a generalized cloud chamber is described, including multiparticle case.
Relation to the GRW spontaneous localization model is discussed. The second
revised version of the paper contains references to papers by other authors
that are are aiming in the same direction: to enhance quantum theory in such a
way that it will provide stochastic description of events triggered by
individual quantum systems.Comment: 20 page
Experimental demonstration of quantum correlations over more than 10 km
Energy and time entangled photons at a wavelength of 1310 nm are produced by
parametric downconversion in a KNbO3 crystal and are sent into all-fiber
interferometers using a telecom fiber network. The two interferometers of this
Franson-type test of the Bell-inequality are located 10.9 km apart from one
another. Two-photon fringe visibilities of up to 81.6 % are obtained. These
strong nonlocal correlations support the nonlocal predictions of quantum
mechanics and provide evidence that entanglement between photons can be
maintained over long distances.Comment: 5 pages, REVTeX, 3 postscript figures include
Quantum Theory and Time Asymmetry
The relation between quantum measurement and thermodynamically irreversible
processes is investigated. The reduction of the state vector is fundamentally
asymmetric in time and shows an observer-relatedness which may explain the
double interpretation of the state vector as a representation of physical
states as well as of information about them. The concept of relevance being
used in all statistical theories of irreversible thermodynamics is shown to be
based on the same observer-relatedness. Quantum theories of irreversible
processes implicitly use an objectivized process of state vector reduction. The
conditions for the reduction are discussed, and I speculate that the final
(subjective) observer system might even be carried by a spacetime point.Comment: Latex version of a paper published in 1979 (with minor revisions), 18
page
Interpreting Quantum Particles as Conceptual Entities
We elaborate an interpretation of quantum physics founded on the hypothesis
that quantum particles are conceptual entities playing the role of
communication vehicles between material entities composed of ordinary matter
which function as memory structures for these quantum particles. We show in
which way this new interpretation gives rise to a natural explanation for the
quantum effects of interference and entanglement by analyzing how interference
and entanglement emerge for the case of human concepts. We put forward a scheme
to derive a metric based on similarity as a predecessor for the structure of
'space, time, momentum, energy' and 'quantum particles interacting with
ordinary matter' underlying standard quantum physics, within the new
interpretation, and making use of aspects of traditional quantum axiomatics.
More specifically, we analyze how the effect of non-locality arises as a
consequence of the confrontation of such an emerging metric type of structure
and the remaining presence of the basic conceptual structure on the fundamental
level, with the potential of being revealed in specific situations.Comment: 19 pages, 1 figur
Prevalence and trends of selected urologic conditions for VA healthcare users
BACKGROUND: Conducted as part of the Urologic Diseases in America project whose aim was to quantify the burden of urologic diseases on the American public, this study focuses on Veterans Health Administration (VHA) users as a special population to supplement data on overall prevalence rates and trends in the United States. Veterans comprise 25% of the male population 18 years or older and contribute substantially to the overall burden of urologic conditions. The objective of this study is to describe the prevalence rates and trends of urologic cancers and selected benign conditions from 1999 to 2002 for VHA users. METHODS: VHA administrative files for 1999 – 2002 and Medicare claims files for the same years were used to identify those who had a diagnosis of qualifying urologic conditions. RESULTS: Among the conditions evaluated, prostate cancer was listed as a primary diagnosis for 5.4% of VHA users in 2002, followed in decreasing prevalence by erectile dysfunction (2.9%), renal mass (1.5%), interstitial cystitis (1.4%), and prostatitis (1.1%). Age-adjusted rates showed significant increases for renal mass (31%), interstitial cystitis (14%), and erectile dysfunction (8%) between 1999 and 2002. Systematic variations in prevalence rates and trends were observed by age, race/ethnicity, and region. Those in the Western region generally had lower age-adjusted prevalence rates and their increases were also slower than other regions. Addition of Medicare data resulted in large increases (21 to 489%) in prevalence among VHA users, suggesting substantial amount of non-VA urological care provided to VHA users. CONCLUSION: Prevalence rates for many urologic diseases increased between 1999 and 2002, which were not entirely attributable to the aging of veterans. This changing urologic disease burden has substantial implications for access to urologic care and treatment capacity, especially in light of the level of urologic care delivered to veterans by Medicare providers outside the VA. Further study on the factors associated with these increases and how they affect the patterns, cost, and quality of care in veterans is needed
Differential contributions of peripheral and central mechanisms to pain in a rodent model of osteoarthritis
The mechanisms underlying the transition from acute nociceptive pain to centrally maintained chronic pain are not clear. We have studied the contributions of the peripheral and central nervous systems during the development of osteoarthritis (OA) pain. Male Sprague-Dawley rats received unilateral intra-articular injections of monosodium iodoacetate (MIA 1mg) or saline, and weight bearing (WB) asymmetry and distal allodynia measured. Subgroups of rats received intra-articular injections of, QX-314 (membrane impermeable local anaesthetic)+capsaicin, QX-314, capsaicin or vehicle on days 7, 14 or 28 post-MIA and WB and PWT remeasured. On days 7&14 post-MIA, but not day 28, QX-314+capsaicin signfcantly attenuated changes in WB induced by MIA, illustrating a crucial role for TRPV1 expressing nociceptors in early OA pain. The role of top-down control of spinal excitability was investigated. The mu-opioid receptor agonist DAMGO was microinjected into the rostroventral medulla, to activate endogenous pain modulatory systems, in MIA and control rats and refex excitability measured using electromyography. DAMGO (3ng) had a signifcantly larger inhibitory effect in MIA treated rats than in controls. These data show distinct temporal contribtuions of TRPV1 expressing nociceptors and opioidergic pain control systems at later timepoints