2,555 research outputs found
Quantum boundary currents for nonsimply-laced Toda theories
We study the quantum integrability of nonsimply--laced affine Toda theories
defined on the half--plane and explicitly construct the first nontrivial
higher--spin charges in specific examples. We find that, in contradistinction
to the classical case, addition of total derivative terms to the "bulk" current
plays a relevant role for the quantum boundary conservation.Comment: 11 pages, latex, no figure
Thermal equilibrium of two quantum Brownian particles
The influence of the environment in the thermal equilibrium properties of a
bipartite continuous variable quantum system is studied. The problem is treated
within a system-plus-reservoir approach. The considered model reproduces the
conventional Brownian motion when the two particles are far apart and induces
an effective interaction between them, depending on the choice of the spectral
function of the bath. The coupling between the system and the environment
guarantees the translational invariance of the system in the absence of an
external potential. The entanglement between the particles is measured by the
logarithmic negativity, which is shown to monotonically decrease with the
increase of the temperature. A range of finite temperatures is found in which
entanglement is still induced by the reservoir.Comment: 8 pages, 1 figur
Protecting the operation from general and residual errors by continuous dynamical decoupling
We study the occurrence of errors in a continuously decoupled two-qubit state
during a quantum operation under decoherence. We consider a
realization of this quantum gate based on the Heisenberg exchange interaction,
which alone suffices for achieving universal quantum computation. Furthermore,
we introduce a continuous-dynamical-decoupling scheme that commutes with the
Heisenberg Hamiltonian to protect it from the amplitude damping and dephasing
errors caused by the system-environment interaction. We consider two
error-protection settings. One protects the qubits from both amplitude damping
and dephasing errors. The other features the amplitude damping as a residual
error and protects the qubits from dephasing errors only. In both settings, we
investigate the interaction of qubits with common and independent environments
separately. We study how errors affect the entanglement and fidelity for
different environmental spectral densities.Comment: Extended version of arXiv:1005.1666. To appear in PR
Thrombus aspiration in patients with ST-elevation myocardial infarction: results of a national registry of interventional cardiology.
BACKGROUND:
We aimed to evaluate the impact of thrombus aspiration (TA) during primary percutaneous coronary intervention (P-PCI) in 'real-world' settings.
METHODS:
We performed a retrospective study, using data from the National Registry of Interventional Cardiology (RNCI 2006-2012, Portugal) with ST-elevation myocardial infarction (STEMI) patients treated with P-PCI. The primary outcome, in-hospital mortality, was analysed through adjusted odds ratio (aOR) and 95% confidence intervals (95%CI).
RESULTS:
We assessed data for 9458 STEMI patients that undergone P-PCI (35% treated with TA). The risk of in-hospital mortality with TA (aOR 0.93, 95%CI:0.54-1.60) was not significantly decreased. After matching patients through the propensity score, TA reduced significantly the risk of in-hospital mortality (OR 0.58, 95%CI:0.35-0.98; 3500 patients).
CONCLUSIONS:
The whole cohort data does not support the routine use of TA in P-PCI, but the results of the propensity-score matched cohort suggests that the use of selective TA may improve the short-term risks of STEMI.info:eu-repo/semantics/publishedVersio
Quantum dynamics in single spin measurement
We study the quantum dynamics of a model for the single-spin measurement in
magnetic-resonance force microscopy. We consider an oscillating driven
cantilever coupled with the magnetic moment of the sample. Then, the cantilever
is damped through an external bath and its readout is provided by a radiation
field. Conditions for reliable measurements will be discussed.Comment: 7 pages, 3 figure
Covariant approach to equilibration in effective field theories
The equilibration of two coupled reservoirs is studied using a Green function
approach which is suitable for future development with the closed time path
method. The problem is solved in two parameterizations, in order to demonstrate
the non-trivial issues of parameterization in both the intermediate steps and
the interpretation of physical quantities. We use a covariant approach to find
self-consistent solutions for the statistical distributions as functions of
time. We show that by formally introducing covariant connections, one can
rescale a slowly varying non-equilibrium theory so that it appears to be an
equilibrium one, for the purposes of calculation. We emphasize the importance
of properly tracking variable redefinitions in order to correctly interpret
physical quantities.Comment: 11 pages, Late
Localization on short-range potentials in dissipative quantum mechanics
In this Letter the problem of the existence of a state localized on a weak
short-range attractive potential in the presence of dissipation is considered.
It is shown that, contrary to the pure quantum case, a localized state is
produced in any number of dimensions, while in low dimensions dissipation leads
to much stronger localization. The results have physical implications for the
dissipative dynamics of objects such as heavy particles in Fermi liquids and
for superconductivity in high- materials.Comment: RevTeX, 4 pages, 1 figure. Published versio
Quantal Brownian Motion - Dephasing and Dissipation
We analyze quantal Brownian motion in dimensions using the unified model
for diffusion localization and dissipation, and Feynman-Vernon formalism. At
high temperatures the propagator possess a Markovian property and we can write
down an equivalent Master equation. Unlike the case of the
Zwanzig-Caldeira-Leggett model, genuine quantum mechanical effects manifest
themselves due to the disordered nature of the environment. Using Wigner
picture of the dynamics we distinguish between two different mechanisms for
destruction of coherence. The analysis of dephasing is extended to the low
temperature regime by using a semiclassical strategy. Various results are
derived for ballistic, chaotic, diffusive, both ergodic and non-ergodic motion.
We also analyze loss of coherence at the limit of zero temperature and clarify
the limitations of the semiclassical approach. The condition for having
coherent effect due to scattering by low-frequency fluctuations is also pointed
out. It is interesting that the dephasing rate can be either larger or smaller
than the dissipation rate, depending on the physical circumstances.Comment: LaTex, 23 pages, 4 figures, published vesio
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