4,423 research outputs found
Synthetic Quantum Systems
So far proposed quantum computers use fragile and environmentally sensitive
natural quantum systems. Here we explore the new notion that synthetic quantum
systems suitable for quantum computation may be fabricated from smart
nanostructures using topological excitations of a stochastic neural-type
network that can mimic natural quantum systems. These developments are a
technological application of process physics which is an information theory of
reality in which space and quantum phenomena are emergent, and so indicates the
deep origins of quantum phenomena. Analogous complex stochastic dynamical
systems have recently been proposed within neurobiology to deal with the
emergent complexity of biosystems, particularly the biodynamics of higher brain
function. The reasons for analogous discoveries in fundamental physics and
neurobiology are discussed.Comment: 16 pages, Latex, 1 eps figure fil
Can a Logarithmically Running Coupling Mimic a String Tension?
It is shown that a Coulomb potential using a running coupling slightly
modified from the perturbative form can produce an interquark potential that
appears nearly linear over a large distance range. Recent high-statistics SU(2)
lattice gauge theory data fit well to this potential without the need for a
linear string-tension term. This calls into question the accuracy of string
tension measurements which are based on the assumption of a constant
coefficient for the Coulomb term. It also opens up the possibility of obtaining
an effectively confining potential from gluon exchange alone.Comment: 13 pages, LaTeX, two figures not included, available from author.
revision - Line lengths fixed so it will tex properl
Hydrogen atom in phase space. The Kirkwood-Rihaczek representation
We present a phase-space representation of the hydrogen atom using the
Kirkwood-Rikaczek distribution function. This distribution allows us to obtain
analytical results, which is quite unique because an exact analytical form of
the Wigner functions corresponding to the atom states is not known. We show how
the Kirkwood-Rihaczek distribution reflects properties of the hydrogen atom
wave functions in position and momentum representations.Comment: 5 pages (and 5 figures
Nonperturbative aspects of the quark-photon vertex
The electromagnetic interaction with quarks is investigated through a
relativistic, electromagnetic gauge-invariant treatment. Gluon dressing of the
quark-photon vertex and the quark self-energy functions is described by the
inhomogeneous Bethe-Salpeter equation in the ladder approximation and the
Schwinger-Dyson equation in the rainbow approximation respectively. Results for
the calculation of the quark-photon vertex are presented in both the time-like
and space-like regions of photon momentum squared, however emphasis is placed
on the space-like region relevant to electron scattering. The treatment
presented here simultaneously addresses the role of dynamically generated
vector bound states and the approach to asymptotic behavior. The
resulting description is therefore applicable over the entire range of momentum
transfers available in electron scattering experiments. Input parameters are
limited to the model gluon two-point function, which is chosen to reflect
confinement and asymptotic freedom, and are largely constrained by the obtained
bound-state spectrum.Comment: 8 figures available on request by email, 25 pages, Revtex,
DOE/ER/40561-131-INT94-00-5
Remote state preparation and teleportation in phase space
Continuous variable remote state preparation and teleportation are analyzed
using Wigner functions in phase space. We suggest a remote squeezed state
preparation scheme between two parties sharing an entangled twin beam, where
homodyne detection on one beam is used as a conditional source of squeezing for
the other beam. The scheme works also with noisy measurements, and provide
squeezing if the homodyne quantum efficiency is larger than 50%. Phase space
approach is shown to provide a convenient framework to describe teleportation
as a generalized conditional measurement, and to evaluate relevant degrading
effects, such the finite amount of entanglement, the losses along the line, and
the nonunit quantum efficiency at the sender location.Comment: 2 figures, revised version to appear in J.Opt.
Squeezed gluon vacuum and the global colour model of QCD
We discuss how the vacuum model of Celenza and Shakin with a squeezed gluon
condensate can explain the existence of an infrared singular gluon propagator
frequently used in calculations within the global colour model. In particular,
it reproduces a recently proposed QCD-motivated model where low energy chiral
parameters were computed as a function of a dynamically generated gluon mass.
We show how the strength of the confining interaction of this gluon propagator
and the value of the physical gluon condensate may be connected.Comment: 13 pages, LaTe
Risk of neuropsychiatric and cardiovascular adverse events following treatment with varenicline and nicotine replacement therapy in the UK Clinical Practice Research Datalink:a case-crossover study
BACKGROUND AND AIMS: Varenicline and nicotine replacement therapy (NRT) are the most commonly used medications to quit smoking. Given their widespread use, monitoring adverse risks remains important. This study aimed to estimate the neuropsychiatric and cardiovascular risks associated with varenicline and NRT as used in routine UK care.DESIGN: Case crossover study.SETTING: UK based electronic primary care records in the Clinical Practice Research Datalink from 2006 to 2015 linked to hospital and mortality datasets.PARTICIPANTS: Adult smokers (n=?) observed in periods when exposed and not exposed to either varenicline or NRT.MEASUREMENTS: Main outcomes included suicide, self-harm, myocardial infarction (MI), all-cause death and cause-specific death (MI, chronic obstructive pulmonary disease (COPD)). In primary analyses, conditional logistic regression was used to compare the chance of varenicline or NRT exposure in the risk period (90 days prior to the event) with the chance of exposure in an earlier single reference period (91-180 days prior to the event) or multiple 90-day reference periods to increase statistical power.FINDINGS: In the primary analyses, findings were inconclusive for the associations between varenicline and the main outcomes using a single reference period, whilst NRT was associated with MI (Odds ratio (OR) 1.40, 95% Confidence interval (CI) 1.18-1.67). Using multiple reference periods, varenicline was associated with an increased risk of self-harm (OR 1.32, 95% CI 1.12-1.56) and suicide (OR 3.56, 95% CI 1.32-9.60) but a reduction in all-cause death (OR 0.75, 95% CI 0.61-0.93). NRT was associated with MI (OR 1.54, 95% CI 1.36-1.74), self-harm (OR 1.30, 95% CI 1.18-1.44), and deaths from MI (OR 1.53, 95% CI 1.11-2.10), COPD (OR 1.33, 95% CI 1.14-1.56) and all causes (OR 1.28, 95% CI 1.18-1.40) when using multiple reference periods.CONCLUSIONS: There appear to be positive associations between 1) nicotine replacement therapy (NRT) and myocardial infarction, death, and risk of self-harm and 2) varenicline and increased risk of self-harm and suicide, as well as a negative association between varenicline and all-cause death. The associations may not be causal. They may reflect health changes at the time of smoking cessation (NRT is prescribed for people with cardiac problems) or be associated with quit attempts (exposure to both medicines was associated with self-harm).</p
The modern tools of quantum mechanics (A tutorial on quantum states, measurements, and operations)
This tutorial is devoted to review the modern tools of quantum mechanics,
which are suitable to describe states, measurements, and operations of
realistic, not isolated, systems in interaction with their environment, and
with any kind of measuring and processing devices. We underline the central
role of the Born rule and and illustrate how the notion of density operator
naturally emerges, together the concept of purification of a mixed state. In
reexamining the postulates of standard quantum measurement theory, we
investigate how they may formally generalized, going beyond the description in
terms of selfadjoint operators and projective measurements, and how this leads
to the introduction of generalized measurements, probability operator-valued
measures (POVM) and detection operators. We then state and prove the Naimark
theorem, which elucidates the connections between generalized and standard
measurements and illustrates how a generalized measurement may be physically
implemented. The "impossibility" of a joint measurement of two non commuting
observables is revisited and its canonical implementations as a generalized
measurement is described in some details. Finally, we address the basic
properties, usually captured by the request of unitarity, that a map
transforming quantum states into quantum states should satisfy to be physically
admissible, and introduce the notion of complete positivity (CP). We then state
and prove the Stinespring/Kraus-Choi-Sudarshan dilation theorem and elucidate
the connections between the CP-maps description of quantum operations, together
with their operator-sum representation, and the customary unitary description
of quantum evolution. We also address transposition as an example of positive
map which is not completely positive, and provide some examples of generalized
measurements and quantum operations.Comment: Tutorial. 26 pages, 1 figure. Published in a special issue of EPJ -
ST devoted to the memory of Federico Casagrand
Separability of Two-Party Gaussian States
We investigate the separability properties of quantum two-party Gaussian
states in the framework of the operator formalism for the density operator.
Such states arise as natural generalizations of the entangled state originally
introduced by Einstein, Podolsky, and Rosen. We present explicit forms of
separable and nonseparable Gaussian states.Comment: Brief Report submitted to Physical Review A, 4 pages, 1 figur
Molecular Electroporation and the Transduction of Oligoarginines
Certain short polycations, such as TAT and polyarginine, rapidly pass through
the plasma membranes of mammalian cells by an unknown mechanism called
transduction as well as by endocytosis and macropinocytosis. These
cell-penetrating peptides (CPPs) promise to be medically useful when fused to
biologically active peptides. I offer a simple model in which one or more CPPs
and the phosphatidylserines of the inner leaflet form a kind of capacitor with
a voltage in excess of 180 mV, high enough to create a molecular electropore.
The model is consistent with an empirical upper limit on the cargo peptide of
40--60 amino acids and with experimental data on how the transduction of a
polyarginine-fluorophore into mouse C2C12 myoblasts depends on the number of
arginines in the CPP and on the CPP concentration. The model makes three
testable predictions.Comment: 15 pages, 5 figure
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