1,777 research outputs found
Recoherence in the entanglement dynamics and classical orbits in the N-atom Jaynes-Cummings model
The rise in linear entropy of a subsystem in the N-atom Jaynes-Cummings model
is shown to be strongly influenced by the shape of the classical orbits of the
underlying classical phase space: we find a one-to-one correspondence between
maxima (minima) of the linear entropy and maxima (minima) of the expectation
value of atomic excitation J_z. Since the expectation value of this operator
can be viewed as related to the orbit radius in the classical phase space
projection associated to the atomic degree of freedom, the proximity of the
quantum wave packet to this atomic phase space borderline produces a maximum
rate of entanglement. The consequence of this fact for initial conditions
centered at periodic orbits in regular regions is a clear periodic recoherence.
For chaotic situations the same phenomenon (proximity of the atomic phase space
borderline) is in general responsible for oscillations in the entanglement
properties.Comment: 15 pages (text), 6 figures; to be published in Physical Review
Perturbative expansion for master equation and it applications
We construct generally applicable small-loss rate expansions for the density
operator of an open system. Successive terms of those expansions yield
characteristic loss rates for dissipation processes. Three applications are
presented in order to give further insight into the context of those
expansions. The first application, of a two-level atom coupling to a bosonic
environment, shows the procedure and the advantage of the expansion, whereas
the second application that consists of a single mode field in a cavity with
linewidth due to partial transmission through one mirror illustrates a
practical use of those expansions in quantum measurements, and the third one,
for an atom coupled to modes of a lossy cavity shows the another use of the
perturbative expansion.Comment: 10 pages, 1 figur
Chiral Anomaly and CPT invariance in an implicit momentum space regularization framework
This is the second in a series of two contributions in which we set out to
establish a novel momentum space framework to treat field theoretical
infinities in perturbative calculations when parity-violating objects occur.
Since no analytic continuation on the space-time dimension is effected, this
framework can be particularly useful to treat dimension-specific theories.
Moreover arbitrary local terms stemming from the underlying infinities of the
model can be properly parametrized. We (re)analyse the undeterminacy of the
radiatively generated CPT violating Chern-Simons term within an extended
version of and calculate the Adler-Bardeen-Bell-Jackiw triangle anomaly
to show that our framework is consistent and general to handle the subtleties
involved when a radiative corretion is finite.Comment: 16 pages, LaTeX, version to appear in PR
Experimental proposal for measuring the Gouy phase of matter waves
The Schr\"odinger equation for an atomic beam predicts that it must have a
phase anomaly near the beam waist analogous to the Gouy phase of an
electromagnetic beam. We propose here a feasible experiment which allows for
the direct determination of this anomalous phase using Ramsey interferometry
with Rydberg atoms. Possible experimental limitations are discussed and shown
to be completely under control within the present day technology. We also
discuss how this finding can open the possibility to use the spatial mode
wavefunctions of atoms as q-dits, since the Gouy phase is an essential
ingredient for making rotations in the quantum states.Comment: 9 pages and 3 figure
Atividades para melhoria da adesão à TARV em serviços de saúde do SUS no estado de São Paulo, 2007
Experimental autologous substitute vascular graft for transplantation surgery
Vascular complications in liver transplantation are a major cause of graft failure and mortality. The aim of the study was to create autologous vascular graft without risk of rejection. Posterior rectus fascia sheath lined with peritoneum was used for iliac artery replacement in seven mongrel dogs. The patency was followed by palpation and Doppler ultrasound. The grafts were removed after one month. Five grafts remained patent. The Doppler showed good, relatively increased flow (median flow rate: 383 cm/sec) after one month in all of the cases. Slight increase in diameter was present in all cases. By microscopy the five patent grafts showed viable morphology, fibroblasts, smooth muscle cells and thin fibrin layer in the wall. The grafts were lined partially with a neoendothelial monolayer and a thin fibrin layer. In conclusion, this graft presents an acceptable patency rate and low thrombogenicity, and could be useful in transplantation. Further investigations are needed to study the effect of immunosuppression and rejection on long-term morphology and patency of the grafts
Elastic scattering of hadrons
Colliding high energy hadrons either produce new particles or scatter
elastically with their quantum numbers conserved and no other particles
produced. We consider the latter case here. Although inelastic processes
dominate at high energies, elastic scattering contributes considerably (18-25%)
to the total cross section. Its share first decreases and then increases at
higher energies. Small-angle scattering prevails at all energies. Some
characteristic features are seen that provide informationon the geometrical
structure of the colliding particles and the relevant dynamical mechanisms. The
steep Gaussian peak at small angles is followed by the exponential (Orear)
regime with some shoulders and dips, and then by a power-law drop.
Results from various theoretical approaches are compared with experimental
data. Phenomenological models claiming to describe this process are reviewed.
The unitarity condition predicts an exponential fall for the differential cross
section with an additional substructure to occur exactly between the low
momentum transfer diffraction cone and a power-law, hard parton scattering
regime under high momentum transfer. Data on the interference of the Coulomb
and nuclear parts of amplitudes at extremely small angles provide the value of
the real part of the forward scattering nuclear amplitude.
The real part of the elastic scattering amplitude and the contribution of
inelastic processes to the imaginary part of this amplitude (the so-called
overlap function) at nonforward transferred momenta are also discussed.
Problems related to the scaling behavior of the differential cross section are
considered. The power-law regime at highest momentum transfer is briefly
described.Comment: 72 pages, 11 Figures; modified Physics-Uspekhi 56 (2013)
Measurement of the mass difference and the binding energy of the hypertriton and antihypertriton
According to the CPT theorem, which states that the combined operation of
charge conjugation, parity transformation and time reversal must be conserved,
particles and their antiparticles should have the same mass and lifetime but
opposite charge and magnetic moment. Here, we test CPT symmetry in a nucleus
containing a strange quark, more specifically in the hypertriton. This
hypernucleus is the lightest one yet discovered and consists of a proton, a
neutron, and a hyperon. With data recorded by the STAR
detector{\cite{TPC,HFT,TOF}} at the Relativistic Heavy Ion Collider, we measure
the hyperon binding energy for the hypertriton, and
find that it differs from the widely used value{\cite{B_1973}} and from
predictions{\cite{2019_weak, 1995_weak, 2002_weak, 2014_weak}}, where the
hypertriton is treated as a weakly bound system. Our results place stringent
constraints on the hyperon-nucleon interaction{\cite{Hammer2002,
STAR-antiH3L}}, and have implications for understanding neutron star interiors,
where strange matter may be present{\cite{Chatterjee2016}}. A precise
comparison of the masses of the hypertriton and the antihypertriton allows us
to test CPT symmetry in a nucleus with strangeness for the first time, and we
observe no deviation from the expected exact symmetry
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