5,532 research outputs found
Quantum information as a non-Kolmogorovian generalization of Shannon's theory
In this article we discuss the formal structure of a generalized information
theory based on the extension of the probability calculus of Kolmogorov to a
(possibly) non-commutative setting. By studying this framework, we argue that
quantum information can be considered as a particular case of a huge family of
non-commutative extensions of its classical counterpart. In any conceivable
information theory, the possibility of dealing with different kinds of
information measures plays a key role. Here, we generalize a notion of state
spectrum, allowing us to introduce a majorization relation and a new family of
generalized entropic measures
Standard Model Physics in ATLAS at the start of the LHC
The upcoming start of the LHC will provide the unprecedented possibility to explore TeV scale physics. Before make any measurement it will be of course necessary a good understanding and calibration of the detector. In this talk a description of main analysis possible at the start of LHC within Standard Model physics is given, with particular attention on ``standard candles'' processes and inclusive cross section measurements
Prospects for Electroweak Physics at LHC
This note describes main electroweak physics measurements at LHC with ATLAS and CMS detectors. W and Z boson analysis on early data are summarize together with prospects for high statistics measurements, like di-boson productions and Z forward-backward asymmetry studies
Unified entropic measures of quantum correlations induced by local measurements
We introduce quantum correlations measures based on the minimal change in
unified entropies induced by local rank-one projective measurements, divided by
a factor that depends on the generalized purity of the system in the case of
non-additive entropies. In this way, we overcome the issue of the artificial
increasing of the value of quantum correlations measures based on non-additive
entropies when an uncorrelated ancilla is appended to the system without
changing the computability of our entropic correlations measures with respect
to the previous ones. Moreover, we recover as limiting cases the quantum
correlations measures based on von Neumann and R\'enyi entropies (i.e.,
additive entropies), for which the adjustment factor becomes trivial. In
addition, we distinguish between total and semiquantum correlations and obtain
some relations between them. Finally, we obtain analytical expressions of the
entropic correlations measures for typical quantum bipartite systems.Comment: 10 pages, 1 figur
Quantum synchronization as a local signature of super- and subradiance
We study the relationship between the collective phenomena of super and
subradiance and spontaneous synchronization of quantum systems. To this aim we
revisit the case of two detuned qubits interacting through a pure dissipative
bosonic environment, which contains the minimal ingredients for our analysis.
By using the Liouville formalism, we are able to find analytically the ultimate
connection between these phenomena. We find that dynamical synchronization is
due to the presence of long standing coherence between the ground state of the
system and the subradiant state. We finally show that, under pure dissipation,
the emergence of spontaneous synchronization and of subradiant emission occur
on the same time scale. This reciprocity is broken in the presence of dephasing
noise.Comment: 12 pages, 6 figure
Dispersion of Klauder's temporally stable coherent states for the hydrogen atom
We study the dispersion of the "temporally stable" coherent states for the
hydrogen atom introduced by Klauder. These are states which under temporal
evolution by the hydrogen atom Hamiltonian retain their coherence properties.
We show that in the hydrogen atom such wave packets do not move
quasi-classically; i.e., they do not follow with no or little dispersion the
Keplerian orbits of the classical electron. The poor quantum-classical
correspondence does not improve in the semiclassical limit.Comment: 6 pages, 2 figure
Classical Evolution of Quantum Elliptic States
The hydrogen atom in weak external fields is a very accurate model for the
multiphoton excitation of ultrastable high angular momentum Rydberg states, a
process which classical mechanics describes with astonishing precision. In this
paper we show that the simplest treatment of the intramanifold dynamics of a
hydrogenic electron in external fields is based on the elliptic states of the
hydrogen atom, i.e., the coherent states of SO(4), which is the dynamical
symmetry group of the Kepler problem. Moreover, we also show that classical
perturbation theory yields the {\it exact} evolution in time of these quantum
states, and so we explain the surprising match between purely classical
perturbative calculations and experiments. Finally, as a first application, we
propose a fast method for the excitation of circular states; these are
ultrastable hydrogenic eigenstates which have maximum total angular momentum
and also maximum projection of the angular momentum along a fixed direction. %Comment: 8 Pages, 2 Figures. Accepted for publication in Phys. Rev.
Approximate transformations of bipartite pure-state entanglement from the majorization lattice
We study the problem of deterministic transformations of an \textit{initial}
pure entangled quantum state, , into a \textit{target} pure
entangled quantum state, , by using \textit{local operations and
classical communication} (LOCC). A celebrated result of Nielsen [Phys. Rev.
Lett. \textbf{83}, 436 (1999)] gives the necessary and sufficient condition
that makes this entanglement transformation process possible. Indeed, this
process can be achieved if and only if the majorization relation holds, where and are probability vectors obtained by taking
the squares of the Schmidt coefficients of the initial and target states,
respectively. In general, this condition is not fulfilled. However, one can
look for an \textit{approximate} entanglement transformation. Vidal \textit{et.
al} [Phys. Rev. A \textbf{62}, 012304 (2000)] have proposed a deterministic
transformation using LOCC in order to obtain a target state
most approximate to in terms of
maximal fidelity between them. Here, we show a strategy to deal with
approximate entanglement transformations based on the properties of the
\textit{majorization lattice}. More precisely, we propose as approximate target
state one whose Schmidt coefficients are given by the supremum between
and . Our proposal is inspired on the observation that fidelity does not
respect the majorization relation in general. Remarkably enough, we find that
for some particular interesting cases, like two-qubit pure states or the
entanglement concentration protocol, both proposals are coincident.Comment: Revised manuscript close to the accepted version in Physica A (10
pages, 1 figure
Dynamics of Entanglement and Bell-nonlocality for Two Stochastic Qubits with Dipole-Dipole Interaction
We have studied the analytical dynamics of Bell nonlocality as measured by
CHSH inequality and entanglement as measured by concurrence for two noisy
qubits that have dipole-dipole interaction. The nonlocal entanglement created
by the dipole-dipole interaction is found to be protected from sudden death for
certain initial states
Revival of quantum correlations without system-environment back-action
Revivals of quantum correlations have often been explained in terms of
back-action on quantum systems by their quantum environment(s). Here we
consider a system of two independently evolving qubits, each locally
interacting with a classical random external field. The environments of the
qubits are also independent, and there is no back-action on the qubits.
Nevertheless, entanglement, quantum discord and classical correlations between
the two qubits may revive in this model. We explain the revivals in terms of
correlations in a classical-quantum state of the environments and the qubits.
Although classical states cannot store entanglement on their own, they can play
a role in storing and reviving entanglement. It is important to know how the
absence of back-action, or modelling an environment as classical, affects the
kind of system time evolutions one is able to describe. We find a class of
global time evolutions where back-action is absent and for which there is no
loss of generality in modelling the environment as classical. Finally, we show
that the revivals can be connected with the increase of a parameter used to
quantify non-Markovianity of the single-qubit dynamics.Comment: 8 pages, 4 figures; this version to appear in Phys. Rev.
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