2,187 research outputs found
Quantum Non-Markovianity: Characterization, Quantification and Detection
We present a comprehensive and up to date review on the concept of quantum
non-Markovianity, a central theme in the theory of open quantum systems. We
introduce the concept of quantum Markovian process as a generalization of the
classical definition of Markovianity via the so-called divisibility property
and relate this notion to the intuitive idea that links non-Markovianity with
the persistence of memory effects. A detailed comparison with other definitions
presented in the literature is provided. We then discuss several existing
proposals to quantify the degree of non-Markovianity of quantum dynamics and to
witness non-Markovian behavior, the latter providing sufficient conditions to
detect deviations from strict Markovianity. Finally, we conclude by enumerating
some timely open problems in the field and provide an outlook on possible
research directions.Comment: Review article. Close to published versio
The Role of Natriuretic peptides in Renovascular Hypertension and its correlation with the Evolution of Myocardial Hypertrophy
The interactions between pressure and volume overload that occur in hypertension lead to different patterns of cardiac hypertrophy and to increase in natriuretic peptides (NPs). The profiles of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) synthesis and secretion have been investigated in models of hypertension. However, the different evolution of these profiles during the acute and chronic periods of pressure overload-induced cardiac hypertrophy is still unknown. For this reason, we studied one-kidney, one clip model using Sprague-Dawley rats at weeks 2, 4, 6 and 12 and correlated the evolution of these profiles with cardiac hypertrophy and hypertension. We observed a positive correlation between blood pressure elevation and the degree of cardiac hypertrophy, with a time-dependent increase in both parameters from week 2. Levels of BNP expression showed an early increase after 2 weeks of treatment while ANP increased significantly after 6 weeks. Yet, the increase in ANP expression was gradual, allowing its correlation with hypertrophy and hypertension. The NP expression has a differential response in the early stages of the development of hypertrophy induced by the renovascular model, with an early increase in BNP expression. Once hypertrophy develops, BNP expression is no longer specific and the increase of both NPs depends on and correlates with the degree of cardiac hypertrophy.Fil: Cerrudo, Carolina Susana. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentina. Universidad de Buenos Aires. Facultad de Farmacia y BioquĂmica; ArgentinaFil: Cavallero, Carmen Susana. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentina. Universidad de Buenos Aires. Facultad de Farmacia y BioquĂmica; ArgentinaFil: RodrĂguez Fermepin, Martin. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentina. Universidad de Buenos Aires. Facultad de Farmacia y BioquĂmica; ArgentinaFil: Hertig, Cecilia Margarita. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Instituto de Investigaciones en IngenierĂa GenĂ©tica y BiologĂa Molecular "Dr. HĂ©ctor N. Torres"; ArgentinaFil: Fernandez, Belisario Enrique. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentina. Universidad de Buenos Aires. Facultad de Farmacia y BioquĂmica; Argentin
Noise-enhanced classical and quantum capacities in communication networks
The unavoidable presence of noise is thought to be one of the major problems
to solve in order to pave the way for implementing quantum information
technologies in realistic physical platforms. However, here we show a clear
example in which noise, in terms of dephasing, may enhance the capability of
transmitting not only classical but also quantum information, encoded in
quantum systems, through communication networks. In particular, we find
analytically and numerically the quantum and classical capacities for a large
family of quantum channels and show that these information transmission rates
can be strongly enhanced by introducing dephasing noise in the complex network
dynamics.Comment: 4 pages, 4 figures; See Video Abstract at
http://www.quantiki.org/video_abstracts/1003587
Open systems with error bounds: spin boson model with spectral density variations
In the study of open quantum systems, one of the most common ways to describe
environmental effects on the reduced dynamics is through the spectral density.
However, in many models this object cannot be computed from first principles
and needs to be inferred on phenomenological grounds or fitted to experimental
data. Consequently, some uncertainty regarding its form and parameters is
unavoidable; this in turn calls into question the accuracy of any theoretical
predictions based on a given spectral density. Here, we focus on the spin-boson
model as a prototypical open quantum system, and find two error bounds on
predicted expectation values in terms of the spectral density variation
considered, and state a sufficient condition for the strongest one to apply. We
further demonstrate an application of our result, by bounding the error brought
about by the approximations involved in the Hierarchical Equations of Motion
resolution method for spin-boson dynamics.Comment: 5+5 pages, minor edits since last unpublished versio
Non-perturbative treatment of non-Markovian dynamics of open quantum systems
We identify the conditions that guarantee equivalence of the reduced dynamics
of an open quantum system (OQS) for two different types of environments - one a
continuous bosonic environment leading to a unitary system-environment
evolution and the other a discrete-mode bosonic environment resulting in a
system-mode (non-unitary) Lindbladian evolution. Assuming initial Gaussian
states for the environments, we prove that the two OQS dynamics are equivalent
if both the expectation values and two-time correlation functions of the
environmental interaction operators are the same at all times for the two
configurations. Since the numerical and analytical description of a
discrete-mode environment undergoing a Lindbladian evolution is significantly
more efficient than that of a continuous bosonic environment in a unitary
evolution, our result represents a powerful, non-perturbative tool to describe
complex and possibly highly non-Markovian dynamics. As a special application,
we recover and generalize the well-known pseudomodes approach to open system
dynamics.Comment: 5+4 pages, 2 figures, Close to the version accepted for publication
in Physical Review Letter
- âŠ