219 research outputs found
Quenching and generation of random states in a kicked Ising model
The kicked Ising model with both a pulsed transverse and a continuous
longitudinal field is studied numerically. Starting from a large transverse
field and a state that is nearly an eigenstate, the pulsed transverse field is
quenched with a simultaneous enhancement of the longitudinal field. The
generation of multipartite entanglement is observed along with a phenomenon
akin to quantum resonance when the entanglement does not evolve for certain
values of the pulse duration. Away from the resonance, the longitudinal field
can drive the entanglement to near maximum values that is shown to agree well
with those of random states. Further evidence is presented that the time
evolved states obtained do have some statistical properties of such random
states. For contrast the case when the fields have a steady value is also
discussed.Comment: 7 pages, 7 figure
Testing statistical bounds on entanglement using quantum chaos
Previous results indicate that while chaos can lead to substantial entropy
production, thereby maximizing dynamical entanglement, this still falls short
of maximality. Random Matrix Theory (RMT) modeling of composite quantum
systems, investigated recently, entails an universal distribution of the
eigenvalues of the reduced density matrices. We demonstrate that these
distributions are realized in quantized chaotic systems by using a model of two
coupled and kicked tops. We derive an explicit statistical universal bound on
entanglement, that is also valid for the case of unequal dimensionality of the
Hilbert spaces involved, and show that this describes well the bounds observed
using composite quantized chaotic systems such as coupled tops.Comment: 5 pages, 3 figures, to appear in PRL. New title. Revised abstract and
some changes in the body of the pape
Entanglement production in Quantized Chaotic Systems
Quantum chaos is a subject whose major goal is to identify and to investigate
different quantum signatures of classical chaos. Here we study entanglement
production in coupled chaotic systems as a possible quantum indicator of
classical chaos. We use coupled kicked tops as a model for our extensive
numerical studies. We find that, in general, presence of chaos in the system
produces more entanglement. However, coupling strength between two subsystems
is also very important parameter for the entanglement production. Here we show
how chaos can lead to large entanglement which is universal and describable by
random matrix theory (RMT). We also explain entanglement production in coupled
strongly chaotic systems by deriving a formula based on RMT. This formula is
valid for arbitrary coupling strengths, as well as for sufficiently long time.
Here we investigate also the effect of chaos on the entanglement production for
the mixed initial state. We find that many properties of the mixed state
entanglement production are qualitatively similar to the pure state
entanglement production. We however still lack an analytical understanding of
the mixed state entanglement production in chaotic systems.Comment: 16 pages, 5 figures. To appear in Pramana:Journal of Physic
Localized Entanglement in one-dimensional Anderson model
The entanglement in one-dimensional Anderson model is studied. We show that
the pairwise entanglement measured by the average concurrence has a direct
relation to the localization length. The numerical study indicates that the
disorder significantly reduces the average entanglement, and entanglement
distribution clearly displays the entanglement localization. The maximal
pairwise entanglement exhibits a maximum as the disorder strength
increases,experiencing a transition from increase to decrease. The entanglement
between the center of localization and other site decreases exponentially along
the spatial direction. Finally,we study effects of disorder on dynamical
properties of entanglement.Comment: 5 pages, 6 figure
Assessment of KaraShieldTM properties in supporting the immune health of healthy subjects: a randomized, parallel, double-blind, placebo-controlled clinical study
Background: This study aims to investigate whether a novel herbal extract blend, KaraShieldTM could be used to help build a healthy immune system that could reduce the number of incidences or severity of common upper respiratory tract infections (URTIs).
Methods: A randomized, parallel, double-blind, placebo-controlled clinical study of 60 days was done on 120 healthy subjects allocated to a treatment arm (500 mg/day, KaraShieldTM) or placebo arm (500 mg/day).
Results: A 500 mg daily dosage of KaraShieldTM significantly improved the subjects' immune health as measured by parameters such as the frequency and severity of upper respiratory tract conditions, the serum IgG level, mean ISQ raw score, WURSS scale score, CRP level in the serum and WHOQOL-BREF score at the end of the study period of sixty days from the baseline compared to that of the placebo. The investigated product was found to be safe and well tolerated by the subjects.
Conclusions: KaraShieldTM may represent a promising safe and effective formulation for building a healthy immune system that could then counteract URTIs
Neurology training around the world
Lancet Neurol. 2003 Sep;2(9):572-9.
Neurology training around the world.
Hooker J, Eccher M, Lakshminarayan K, Souza-Lima FC, Rejdak K, Kwiecinski H, Corea F, Lima JM.
The National Hospital for Neurology and Neurosurgery, Queen Square, WC1N 3BG, London, UK.
Comment in:
Lancet Neurol. 2003 Oct;2(10):594; discussion 594
Entanglement, avoided crossings and quantum chaos in an Ising model with a tilted magnetic field
We study a one-dimensional Ising model with a magnetic field and show that
tilting the field induces a transition to quantum chaos. We explore the
stationary states of this Hamiltonian to show the intimate connection between
entanglement and avoided crossings. In general entanglement gets exchanged
between the states undergoing an avoided crossing with an overall enhancement
of multipartite entanglement at the closest point of approach, simultaneously
accompanied by diminishing two-body entanglement as measured by concurrence. We
find that both for stationary as well as nonstationary states, nonintegrability
leads to a destruction of two-body correlations and distributes entanglement
more globally.Comment: Corrections in two figure captions and one new reference. To appear
in Phys. Rev.
Semiclassical properties and chaos degree for the quantum baker's map
We study the chaotic behaviour and the quantum-classical correspondence for
the baker's map. Correspondence between quantum and classical expectation
values is investigated and it is numerically shown that it is lost at the
logarithmic timescale. The quantum chaos degree is computed and it is
demonstrated that it describes the chaotic features of the model. The
correspondence between classical and quantum chaos degrees is considered.Comment: 30 pages, 4 figures, accepted for publication in J. Math. Phy
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