1,140 research outputs found
Open Quantum Dynamics: Complete Positivity and Entanglement
We review the standard treatment of open quantum systems in relation to
quantum entanglement, analyzing, in particular, the behaviour of bipartite
systems immersed in a same environment. We first focus upon the notion of
complete positivity, a physically motivated algebraic constraint on the quantum
dynamics, in relation to quantum entanglement, i.e. the existence of
statistical correlations which can not be accounted for by classical
probability. We then study the entanglement power of heat baths versus their
decohering properties, a topic of increasing importance in the framework of the
fast developing fields of quantum information, communication and computation.
The presentation is self contained and, through several examples, it offers a
detailed survey of the physics and of the most relevant and used techniques
relative to both quantum open system dynamics and quantum entanglement.Comment: LaTex, 77 page
Damped harmonic oscillators in the holomorphic representation
Quantum dynamical semigroups are applied to the study of the time evolution
of harmonic oscillators, both bosonic and fermionic. Explicit expressions for
the density matrices describing the states of these systems are derived using
the holomorphic representation. Bosonic and fermionic degrees of freedom are
then put together to form a supersymmetric oscillator; the conditions that
assure supersymmetry invariance of the corresponding dynamical equations are
explicitly derived.Comment: 19 pages, plain-TeX, no figure
Planck's scale dissipative effects in atom interferometry
Atom interferometers can be used to study phenomena leading to
irreversibility and dissipation, induced by the dynamics of fundamental objects
(strings and branes) at a large mass scale. Using an effective, but physically
consistent description in terms of a master equation of Lindblad form, the
modifications of the interferometric pattern induced by the new phenomena are
analyzed in detail. We find that present experimental devices can in principle
provide stringent bounds on the new effects.Comment: 12 pages, plain-Te
Dissipative quantum metrology in manybody systems of identical particles
Estimation of physical parameters is a must in almost any part of science and
technology. The enhancement of the performances in this task, e.g., beating the
standard classical shot-noise limit, using available physical resources is a
major goal in metrology. Quantum metrology in closed systems has indicated that
entanglement in such systems may be a useful resource. However, it is not yet
fully understood whether in open quantum systems such enhancements may still
show up. Here, we consider a dissipative (open) quantum system of identical
particles in which a parameter of the open dynamics itself is to be estimated.
We employ a recently-developed dissipative quantum metrology framework, and
investigate whether the entanglement produced in the course of the dissipative
dynamics may help the estimation task. Specifically, we show that even in a
Markovian dynamics, in which states become less distinguishable in time, at
small enough times entanglement generated by the dynamics may offer some
advantage over the classical shot-noise limit.Comment: 9 pages, 2 figure
Effective dissipative dynamics for polarized photons
In the framework of open quantum systems, the propagation of polarized
photons can be effectively described using quantum dynamical semigroups. These
extended time-evolutions induce irreversibility and dissipation. Planned, high
sensitive experiments, both in the laboratory and in space, will be able to put
stringent bounds on these non-standard effects.Comment: 15 pages, plain-TeX, no figure
Quantum measuring processes for trapped ultracold bosonic gases
The standard experimental techniques usually adopted in the study of the
behaviour of ultracold atoms in optical lattices involve extracting the atom
density profile from absorption images of the atomic sample after trap release.
Quantum mechanically this procedure is described by a generalized measure
(POVM); interference patterns found in absorption images suggest a generalized
measure based on fixed-phase, coherent-like states. We show that this leads to
an average atomic density which differs from the usually adopted one, obtained
as the expectation value of the atom density operator in the many-body state.Comment: 11 pages, LaTe
Dissipative neutrino oscillations in randomly fluctuating matter
The generalized dynamics describing the propagation of neutrinos in randomly
fluctuating media is analyzed: it takes into account matter-induced,
decoherence phenomena that go beyond the standard MSW effect. A widely adopted
density fluctuation pattern is found to be physically untenable: a more general
model needs to be instead considered, leading to flavor changing effective
neutrino-matter interactions. They induce new, dissipative effects that modify
the neutrino oscillation pattern in a way amenable to a direct experimental
analysis.Comment: 14 pages, plain-Te
Quantum contextuality in N-boson systems
Quantum contextuality in systems of identical bosonic particles is explicitly
exhibited via the maximum violation of a suitable inequality of
Clauser-Horne-Shimony-Holt type. Unlike the approaches considered so far, which
make use of single-particle observables, our analysis involves collective
observables constructed using multi-boson operators. An exemplifying scheme to
test this violation with a quantum optical setup is also discussed.Comment: 4 pages, 1 figure, LaTe
Quantum Dissipative Effects and Neutrinos : current constraints and future perspectives
We establish the most stringent experimental constraints coming from recent
terrestrial neutrino experiments on quantum mechanical decoherence effects in
neutrino systems. Taking a completely phenomenological approach, we probe
vacuum oscillations plus quantum decoherence between two neutrino species in
the channels , and , admitting that the quantum decoherence parameter is related
to the neutrino energy as : ,
with and 2. Our bounds are valid for a neutrino mass squared
difference compatible with the atmospheric, the solar and, in many cases, the
LSND scale. We also qualitatively discuss the perspectives of the future long
baseline neutrino experiments to further probe quantum dissipation.Comment: 26 pages, 8 encapsulated postscript figure
Correlations in quantum thermodynamics: Heat, work, and entropy production
We provide a characterization of energy in the form of exchanged heat and
work between two interacting constituents of a closed, bipartite, correlated
quantum system. By defining a binding energy we derive a consistent quantum
formulation of the first law of thermodynamics, in which the role of
correlations becomes evident, and this formulation reduces to the standard
classical picture in relevant systems. We next discuss the emergence of the
second law of thermodynamics under certain---but fairly general---conditions
such as the Markovian assumption. We illustrate the role of correlations and
interactions in thermodynamics through two examples.Comment: 16 page
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