302 research outputs found
Quantum ergodicity and entanglement in kicked coupled-tops
We study the dynamical generation of entanglement as a signature of chaos in
a system of periodically kicked coupled-tops, where chaos and entanglement
arise from the same physical mechanism. The long-time averaged entanglement as
a function of the position of an initially localized wave packet very closely
correlates with the classical phase space surface of section -- it is nearly
uniform in the chaotic sea, and reproduces the detailed structure of the
regular islands. The uniform value in the chaotic sea is explained by the
random state conjecture. As classically chaotic dynamics take localized
distributions in phase space to random distributions, quantized versions take
localized coherent states to pseudo-random states in Hilbert space. Such random
states are highly entangled, with an average value near that of the maximally
entangled state. For a map with global chaos, we derive that value based on new
analytic results for the typical entanglement in a subspace defined by the
symmetries of the system.
For a mixed phase space, we use the Percival conjecture to identify a
"chaotic subspace" of the Hilbert space. The typical entanglement, averaged
over the unitarily invariant Haar measure in this subspace, agrees with the
long-time averaged entanglement for initial states in the chaotic sea. In all
cases the dynamically generated entanglement is predicted by a unitary ensemble
of random states, even though the system is time-reversal invariant, and the
Floquet operator is a member of the circular orthogonal ensemble.Comment: 12 pages with 8 figure
Operational Significance of Discord Consumption: Theory and Experiment
Coherent interactions that generate negligible entanglement can still exhibit
unique quantum behaviour. This observation has motivated a search beyond
entanglement for a complete description of all quantum correlations. Quantum
discord is a promising candidate. Here, we demonstrate that under certain
measurement constraints, discord between bipartite systems can be consumed to
encode information that can only be accessed by coherent quantum interactions.
The inability to access this information by any other means allows us to use
discord to directly quantify this `quantum advantage'. We experimentally encode
information within the discordant correlations of two separable Gaussian
states. The amount of extra information recovered by coherent interaction is
quantified and directly linked with the discord consumed during encoding. No
entanglement exists at any point of this experiment. Thus we introduce and
demonstrate an operational method to use discord as a physical resource.Comment: 10 pages, 3 figures, updated with Nature Physics Reference,
simplified proof in Appendi
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The relationship between group identification and satisfaction with life in a cross-cultural community sample
A variety of studies have shown that group identification (a sense of belonging to one’s social group, coupled with a sense of commonality with the group’s members) is linked to high levels of satisfaction with life (SWL). The aim of the present study was to support and extend this literature by: i) investigating the link between group identification and SWL with a large cross-cultural community sample; ii) examining whether the relationship is moderated by nationality; and iii) considering whether SWL is enhanced by possessing multiple group identifications simultaneously. Utilizing data from Wave 1 of the Health in Groups project, 3,829 participants from both Scotland and Italy completed a questionnaire assessing their identification with their family, their local community, and a group of their choice, as well as their level of SWL. Higher identification with each group predicted higher SWL. Nationality was a marginal moderator of the relationship between family identification and SWL, with the relationship being stronger for Italian participants than for Scottish participants. There was also an additive effect of group identification, with a positive relationship between the number of groups with which participants identified and their SWL. These effects were obtained even after controlling for gender, age, employment status, nationality, and extent of contact with each group. The implications for healthcare professionals and their patients are discussed
Negativity and quantum discord in Davies environments
We investigate the time evolution of negativity and quantum discord for a
pair of non-interacting qubits with one being weakly coupled to a decohering
Davies--type Markovian environment. At initial time of preparation, the qubits
are prepared in one of the maximally entangled pure Bell states. In the
limiting case of pure decoherence (i.e. pure dephasing), both, the quantum
discord and negativity decay to zero in the long time limit. In presence of a
manifest dissipative dynamics, the entanglement negativity undergoes a sudden
death at finite time while the quantum discord relaxes continuously to zero
with increasing time. We find that in dephasing environments the decay of the
negativity is more propitious with increasing time; in contrast, the evolving
decay of the quantum discord proceeds weaker for dissipative environments.
Particularly, the slowest decay of the quantum discord emerges when the energy
relaxation time matches the dephasing time.Comment: submitted for publicatio
The classical-quantum boundary for correlations: discord and related measures
One of the best signatures of nonclassicality in a quantum system is the
existence of correlations that have no classical counterpart. Different methods
for quantifying the quantum and classical parts of correlations are amongst the
more actively-studied topics of quantum information theory over the past
decade. Entanglement is the most prominent of these correlations, but in many
cases unentangled states exhibit nonclassical behavior too. Thus distinguishing
quantum correlations other than entanglement provides a better division between
the quantum and classical worlds, especially when considering mixed states.
Here we review different notions of classical and quantum correlations
quantified by quantum discord and other related measures. In the first half, we
review the mathematical properties of the measures of quantum correlations,
relate them to each other, and discuss the classical-quantum division that is
common among them. In the second half, we show that the measures identify and
quantify the deviation from classicality in various
quantum-information-processing tasks, quantum thermodynamics, open-system
dynamics, and many-body physics. We show that in many cases quantum
correlations indicate an advantage of quantum methods over classical ones.Comment: Close to the published versio
Quantum Discord and entropic measures of quantum correlations: Optimization and behavior in finite spin chains
We discuss a generalization of the conditional entropy and one-way
information deficit in quantum systems, based on general entropic forms. The
formalism allows to consider simple entropic forms for which a closed
evaluation of the associated optimization problem in qudit-qubit systems is
shown to become feasible, allowing to approximate that of the quantum discord.
As application, we examine quantum correlations of spin pairs in the exact
ground state of finite spin chains in a magnetic field through the quantum
discord and information deficit. While these quantities show a similar
behavior, their optimizing measurements exhibit significant differences, which
can be understood and predicted through the previous approximations. The
remarkable behavior of these quantities in the vicinity of transverse and
non-transverse factorizing fields is also discussed.Comment: 10 pages, 3 figure
A replication study confirms the association of TNFSF4 (OX40L) polymorphisms with systemic sclerosis in a large European cohort
<p><b>Objectives</b> The aim of this study was to confirm the influence of TNFSF4 polymorphisms on systemic sclerosis (SSc) susceptibility and phenotypic features.</p>
<p><b>Methods</b> A total of 8 European populations of Caucasian ancestry were included, comprising 3014 patients with SSc and 3125 healthy controls. Four genetic variants of TNFSF4 gene promoter (rs1234314, rs844644, rs844648 and rs12039904) were selected as genetic markers.</p>
<p><b>Results</b> A pooled analysis revealed the association of rs1234314 and rs12039904 polymorphisms with SSc (OR 1.15, 95% CI 1.02 to 1.31; OR 1.18, 95% CI 1.08 to 1.29, respectively). Significant association of the four tested variants with patients with limited cutaneous SSc (lcSSc) was revealed (rs1234314 OR 1.22, 95% CI 1.07 to 1.38; rs844644 OR 0.91, 95% CI 0.83 to 0.99; rs844648 OR 1.10, 95% CI 1.01 to 1.20 and rs12039904 OR 1.20, 95% CI 1.09 to 1.33). Association of rs1234314, rs844648 and rs12039904 minor alleles with patients positive for anti-centromere antibodies (ACA) remained significant (OR 1.23, 95% CI 1.10 to 1.37; OR 1.12, 95% CI 1.01 to 1.25; OR 1.22, 95% CI 1.07 to 1.38, respectively). Haplotype analysis confirmed a protective haplotype associated with SSc, lcSSc and ACA positive subgroups (OR 0.88, 95% CI 0.82 to 0.96; OR 0.88, 95% CI 0.80 to 0.96; OR 0.86, 95% CI 0.77 to 0.97, respectively) and revealed a new risk haplotype associated with the same groups of patients (OR 1.14, 95% CI 1.03 to 1.26; OR 1.20, 95% CI 1.08 to 1.35; OR 1.23, 95% CI 1.07 to 1.42, respectively).</p>
<p><b>Conclusions</b> The data confirm the influence of TNFSF4 polymorphisms in SSc genetic susceptibility, especially in subsets of patients positive for lcSSc and ACA.</p>
Quantum Correlations in NMR systems
In conventional NMR experiments, the Zeeman energy gaps of the nuclear spin
ensembles are much lower than their thermal energies, and accordingly exhibit
tiny polarizations. Generally such low-purity quantum states are devoid of
quantum entanglement. However, there exist certain nonclassical correlations
which can be observed even in such systems. In this chapter, we discuss three
such quantum correlations, namely, quantum contextuality, Leggett-Garg temporal
correlations, and quantum discord. In each case, we provide a brief theoretical
background and then describe some results from NMR experiments.Comment: 21 pages, 7 figure
Geometric measure of quantum discord and the geometry of a class of two-qubit states
We investigate the geometric picture of the level surfaces of quantum
entanglement and geometric measure of quantum discord (GMQD) of a class of
X-states, respectively. This pictorial approach provides us a direct
understanding of the structure of entanglement and GMQD. The dynamic evolution
of GMQD under two typical kinds of quantum decoherence channels is also
investigated. It is shown that there exists a class of initial states for which
the GMQD is not destroyed by decoherence in a finite time interval.
Furthermore, we establish a factorization law between the initial and final
GMQD, which allows us to infer the evolution of entanglement under the
influences of the environment.Comment: 10 pages, 4 figures, comments are welcom
Frozen and Invariant Quantum Discord under Local Dephasing Noise
In this chapter, we intend to explore and review some remarkable dynamical
properties of quantum discord under various different open quantum system
models. Specifically, our discussion will include several concepts connected to
the phenomena of time invariant and frozen quantum discord. Furthermore, we
will elaborate on the relation of these two phenomena to the non-Markovian
features of the open system dynamics and to the usage of dynamical decoupling
protocols.Comment: 29 pages, 8 figure
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