112 research outputs found
Quantum Darwinism and non-Markovian dissipative dynamics from quantum phases of the spin-1/2 XX model
Quantum Darwinism explains the emergence of a classical description of
objects in terms of the creation of many redundant registers in an environment
containing their classical information. This amplification phenomenon, where
only classical information reaches the macroscopic observer and through which
different observers can agree on the objective existence of such object, has
been revived lately for several types of situations, successfully explaining
classicality. We explore quantum Darwinism in the setting of an environment
made of two level systems which are initially prepared in the ground state of
the XX model, which exhibits different phases; we find that the different
phases have different ability to redundantly acquire classical information
about the system, being the "ferromagnetic phase" the only one able to complete
quantum Darwinism. At the same time we relate this ability to how non-Markovian
the system dynamics is, based on the interpretation that non-Markovian dynamics
is associated to back flow of information from environment to system, thus
spoiling the information transfer needed for Darwinism. Finally, we explore
mixing of bath registers by allowing a small interaction among them, finding
that this spoils the stored information as previously found in the literature
Probing the spectral density of a dissipative qubit via quantum synchronization
The interaction of a quantum system, which is not accessible by direct
measurement, with an external probe can be exploited to infer specific features
of the system itself. We introduce a probing scheme based on the emergence of
spontaneous quantum synchronization between an out-of-equilibrium qubit, in
contact with an external environment, and a probe qubit. Tuning the frequency
of the probe leads to a transition between synchronization in phase and
antiphase. The sharp transition between these two regimes is locally accessible
by monitoring the probe dynamics alone and allows one to reconstruct the shape
of the spectral density of the environment
Bringing entanglement to the high temperature limit
We show the existence of an entangled nonequilibrium state at very high
temperatures when two linearly coupled harmonic oscillators are parametrically
driven and dissipate into two independent heat baths. This result has a twofold
meaning: first, it fundamentally shifts the classical-quantum border to
temperatures as high as our experimental ability allows us, and second, it can
help increase by at least one order of magnitude the temperature at which
current experimental setups are operated.Comment: accepted in Phys. Rev. Let
Genuine quantum and classical correlations in multipartite systems
Generalizing the quantifiers used to classify correlations in bipartite
systems, we define genuine total, quantum, and classical correlations in
multipartite systems. The measure we give is based on the use of relative
entropy to quantify the "distance" between two density matrices. Moreover, we
show that, for pure states of three qubits, both quantum and classical
bipartite correlations obey a ladder ordering law fixed by two-body mutual
informations, or, equivalently, by one-qubit entropies.Comment: Accepted for publication in Phys. Rev. Let
Information sharing in Quantum Complex Networks
We introduce the use of entanglement entropy as a tool for studying the
amount of information shared between the nodes of quantum complex networks. By
considering the ground state of a network of coupled quantum harmonic
oscillators, we compute the information that each node has on the rest of the
system. We show that the nodes storing the largest amount of information are
not the ones with the highest connectivity, but those with intermediate
connectivity thus breaking down the usual hierarchical picture of classical
networks. We show both numerically and analytically that the mutual information
characterizes the network topology. As a byproduct, our results point out that
the amount of information available for an external node connecting to a
quantum network allows to determine the network topology.Comment: text and title updated, published version [Phys. Rev. A 87, 052312
(2013)
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