338 research outputs found
Complementarity and uncertainty relations for matter wave interferometry
We establish a rigorous quantitative connection between (i) the
interferometric duality relation for which-way information and fringe
visibility and (ii) Heisenberg's uncertainty relation for position and modular
momentum. We apply our theory to atom interferometry, wherein spontaneously
emitted photons provide which way information, and unambiguously resolve the
challenge posed by the metamaterial `perfect lens' to complementarity and to
the Heisenberg-Bohr interpretation of the Heisenberg microscope thought
experiment.Comment: nine pages, five figure
Realistic experiments for measuring the wave function of a single particle
We suggest scattering experiments which implement the concept of ``protective
measurements'' allowing the measurement of the complete wave function even when
only one quantum system (rather than an ensemble) is available. Such scattering
experiments require massive, slow, projectiles with kinetic energies lower than
the first excitation of the system in question. The results of such experiments
can have a (probabilistic) distribution (as is the case when the Born
approximation for the scattering is valid) or be deterministic (in a
semi-classical limit).Comment: LaTeX, 19 pages, 1 epsfi
Quantum Preferred Frame: Does It Really Exist?
The idea of the preferred frame as a remedy for difficulties of the
relativistic quantum mechanics in description of the non-local quantum
phenomena was undertaken by such physicists as J. S. Bell and D. Bohm. The
possibility of the existence of preferred frame was also seriously treated by
P. A. M. Dirac. In this paper, we propose an Einstein-Podolsky-Rosen-type
experiment for testing the possible existence of a quantum preferred frame. Our
analysis suggests that to verify whether a preferred frame of reference in the
quantum world exists it is enough to perform an EPR type experiment with pair
of observers staying in the same inertial frame and with use of the massive EPR
pair of spin one-half or spin one particles.Comment: 5 pp., 6 fig
A simple derivation of Kepler's laws without solving differential equations
Proceeding like Newton with a discrete time approach of motion and a
geometrical representation of velocity and acceleration, we obtain Kepler's
laws without solving differential equations. The difficult part of Newton's
work, when it calls for non trivial properties of ellipses, is avoided by the
introduction of polar coordinates. Then a simple reconsideration of Newton's
figure naturally leads to en explicit expression of the velocity and to the
equation of the trajectory. This derivation, which can be fully apprehended by
beginners at university (or even before) can be considered as a first
application of mechanical concepts to a physical problem of great historical
and pedagogical interest
EPR before EPR: a 1930 Einstein-Bohr thought experiment revisited
In 1930 Einstein argued against consistency of the time-energy uncertainty
relation by discussing a thought experiment involving a measurement of mass of
the box which emitted a photon. Bohr seemingly triumphed over Einstein by
arguing that the Einstein's own general theory of relativity saves the
consistency of quantum mechanics. We revisit this thought experiment from a
modern point of view at a level suitable for undergraduate readership and find
that neither Einstein nor Bohr was right. Instead, this thought experiment
should be thought of as an early example of a system demonstrating nonlocal
"EPR" quantum correlations, five years before the famous
Einstein-Podolsky-Rosen paper.Comment: 11 pages, revised, accepted for publication in Eur. J. Phy
Realization of GHZ States and the GHZ Test via Cavity QED
In this article we discuss the realization of atomic GHZ states involving
three-level atoms and we show explicitly how to use this state to perform the
GHZ test in which it is possible to decide between local realism theories and
quantum mechanics. The experimental realizations proposed makes use of the
interaction of Rydberg atoms with a cavity prepared in a coherent state.Comment: 16 pages and 3 figures. submitted to J. Mod. Op
The Standard Model of Quantum Measurement Theory: History and Applications
The standard model of the quantum theory of measurement is based on an
interaction Hamiltonian in which the observable-to-be-measured is multiplied
with some observable of a probe system. This simple Ansatz has proved extremely
fruitful in the development of the foundations of quantum mechanics. While the
ensuing type of models has often been argued to be rather artificial, recent
advances in quantum optics have demonstrated their prinicpal and practical
feasibility. A brief historical review of the standard model together with an
outline of its virtues and limitations are presented as an illustration of the
mutual inspiration that has always taken place between foundational and
experimental research in quantum physics.Comment: 22 pages, to appear in Found. Phys. 199
Quantum origin of the primordial fluctuation spectrum and its statistics
The usual account for the origin of cosmic structure during inflation is not
fully satisfactory, as it lacks a physical mechanism capable of generating the
inhomogeneity and anisotropy of our Universe, from an exactly homogeneous and
isotropic initial state associated with the early inflationary regime. The
proposal in [A. Perez, H. Sahlmann, and D. Sudarsky, Classical Quantum Gravity,
23, 2317, (2006)] considers the spontaneous dynamical collapse of the wave
function, as a possible answer to that problem. In this work, we review briefly
the difficulties facing the standard approach, as well as the answers provided
by the above proposal and explore their relevance to the investigations
concerning the characterization of the primordial spectrum and other
statistical aspects of the cosmic microwave background and large-scale matter
distribution. We will see that the new approach leads to novel ways of
considering some of the relevant questions, and, in particular, to distinct
characterizations of the non-Gaussianities that might have left imprints on the
available data.Comment: 27 pages. Revision to match the published versio
P.A.M. Dirac and the Discovery of Quantum Mechanics
Dirac's contributions to the discovery of non-relativistic quantum mechanics
and quantum electrodynamics, prior to his discovery of the relativistic wave
equation, are described
The incidence of postoperative vasopressor usage: protocol for a prospective international observational cohort study (SQUEEZE)
Background:
Postoperative hypotension is common after major non-cardiac surgery, due predominantly to vasodilation. Administration of infused vasopressors postoperatively may often be considered a surrogate indicator of vasodilation. The incidence of postoperative vasopressors has never been described for non-cardiac surgery, nor have outcomes associated with their use. This paper presents a protocol for a prospective international cohort study to address these gaps in knowledge.
The primary objectives are to estimate the proportion of patients who receive postoperative vasopressor infusions (PVI) and to document the variation in this proportion between hospitals and internationally. Furthermore, we will identify factors in variation of care (patient, condition, surgery, and intraoperative management) associated with receipt of PVI and investigate how PVI use is associated with patient outcomes, including organ dysfunction, length of hospital stay, and 30-day in-hospital mortality.
Method:
This will be a prospective, international, multicentre cohort study that includes all adult (≥ 18 years) non-cardiac surgical patients in participating centres. Patients undergoing cardiac, obstetric, or day-case surgery will be excluded. We will recruit two cohorts of patients: cohort A will include all eligible patients admitted to participating hospitals for seven consecutive days. Cohort B will include 30 sequential patients per hospital, with the single additional inclusion criterion of postoperative vasopressor usage. We expect to collect data on approximately 40,000 patients for cohort A and 12,800 patients for cohort B.
Discussion:
While in cardiac surgery, clinical trials have informed the choice of vasopressors used to treat postoperative vasoplegia; there remains equipoise over the best approach in non-cardiac surgery. Our study will represent the first large-scale assessment of the use of vasopressors after non-cardiac surgery. These data will inform future studies, including trials of different vasopressors and potential management options to improve outcomes and reduce resource use after surgery.
Trial registration:
ClinicalTrials.gov Identifier: NCT03805230, 15 January 2019
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