1,868 research outputs found
Fidelity Decay as an Efficient Indicator of Quantum Chaos
Recent work has connected the type of fidelity decay in perturbed quantum
models to the presence of chaos in the associated classical models. We
demonstrate that a system's rate of fidelity decay under repeated perturbations
may be measured efficiently on a quantum information processor, and analyze the
conditions under which this indicator is a reliable probe of quantum chaos and
related statistical properties of the unperturbed system. The type and rate of
the decay are not dependent on the eigenvalue statistics of the unperturbed
system, but depend on the system's eigenvector statistics in the eigenbasis of
the perturbation operator. For random eigenvector statistics the decay is
exponential with a rate fixed precisely by the variance of the perturbation's
energy spectrum. Hence, even classically regular models can exhibit an
exponential fidelity decay under generic quantum perturbations. These results
clarify which perturbations can distinguish classically regular and chaotic
quantum systems.Comment: 4 pages, 3 figures, LaTeX; published version (revised introduction
and discussion
Spin-Boson Hamiltonian and Optical Absorption of Molecular Dimers
An analysis of the eigenstates of a symmetry-broken spin-boson Hamiltonian is
performed by computing Bloch and Husimi projections. The eigenstate analysis is
combined with the calculation of absorption bands of asymmetric dimer
configurations constituted by monomers with nonidentical excitation energies
and optical transition matrix elements. Absorption bands with regular and
irregular fine structures are obtained and related to the transition from the
coexistence to a mixing of adiabatic branches in the spectrum. It is shown that
correlations between spin states allow for an interpolation between absorption
bands for different optical asymmetries.Comment: 15 pages, revTeX, 8 figures, accepted for publication in Phys. Rev.
RoboPol: Connection between optical polarization plane rotations and gamma-ray flares in blazars
We use results of our 3 year polarimetric monitoring program to investigate
the previously suggested connection between rotations of the polarization plane
in the optical emission of blazars and their gamma-ray flares in the GeV band.
The homogeneous set of 40 rotation events in 24 sources detected by {\em
RoboPol} is analysed together with the gamma-ray data provided by {\em
Fermi}-LAT. We confirm that polarization plane rotations are indeed related to
the closest gamma-ray flares in blazars and the time lags between these events
are consistent with zero. Amplitudes of the rotations are anticorrelated with
amplitudes of the gamma-ray flares. This is presumably caused by higher
relativistic boosting (higher Doppler factors) in blazars that exhibit smaller
amplitude polarization plane rotations. Moreover, the time scales of rotations
and flares are marginally correlated.Comment: 12 pages, 16 figures, accepted to MNRA
Transition from antibunching to bunching for two dipole-interacting atoms
It is known that there is a transition from photon antibunching to bunching
in the resonance fluorescence of a driven system of two two-level atoms with
dipole-dipole interaction when the atomic distance decreases and the other
parameters are kept fixed. We give a simple explanation for the underlying
mechanism which in principle can also be applied to other systems. PACS numbers
42.50.Ar, 42.50FxComment: Submitted to Phys. Rev. A; 15 pages Latex + 4 figure
Wigner Random Banded Matrices with Sparse Structure: Local Spectral Density of States
Random banded matrices with linearly increasing diagonal elements are
recently considered as an attractive model for complex nuclei and atoms. Apart
from early papers by Wigner \cite{Wig} there were no analytical studies on the
subject. In this letter we present analytical and numerical results for local
spectral density of states (LDOS) for more general case of matrices with a
sparsity inside the band. The crossover from the semicircle form of LDOS to
that given by the Breit-Wigner formula is studied in detail.Comment: Misprints are corrected and stylistic changes are made. To be
published in PR
Washingtonia filifera seed extracts inhibit the islet amyloid polypeptide fibrils formations and α-amylase and α-glucosidase activity
Washingtonia filifera seeds have revealed to possess antioxidant properties, butyrylcholinesterase and xanthine oxidase inhibition activities. The literature has indicated a relationship between Alzheimer’s disease (AD) and type-2 diabetes (T2D). Keeping this in mind, we have now evaluated the inhibitory properties of W. filifera seed extracts on α-amylase, α-glucosidase enzyme activity and the Islet Amyloid Polypeptide (IAPP) fibrils formation. Three extracts from seeds of W. filifera were evaluated for their enzyme inhibitory effect and IC50 values were calculated for all the extracts. The inhibition mode was investigated by Lineweaver-Burk plot analysis and the inhibition of IAPP aggregate formation was monitored. W. filifera methanol seed extract appears as the most potent inhibitor of α-amylase, α-glucosidase, and for the IAPP fibril formation. Current findings indicate new potential of this extract that could be used for the identification or development of novel potential agents for T2D and AD
AGN and starbursts at high redshift: High resolution EVN radio observations of the Hubble Deep Field
We present deep, wide-field European VLBI Network (EVN) 1.6 GHz observations
of the Hubble Deep Field (HDF) region with a resolution of 0.025 arcseconds.
Above the 210 microJy/beam (5sigma) detection level, the EVN clearly detects
two radio sources in a field that encompasses the HDF and part of the Hubble
Flanking Fields (HFF). The sources detected are: VLA J123644+621133 (a z=1.013,
low-luminosity FR-I radio source located within the HDF itself) and VLA
J123642+621331 (a dust enshrouded, optically faint, z=4.424 starburst system).
A third radio source, J123646+621404, is detected at the 4sigma level. The VLBI
detections of all three sources suggest that most of the radio emission of
these particular sources (including the dusty starburst) is generated by an
embedded AGN.Comment: 4 pages, 1 figure; Accepted by Astron. & Astrophys Letters ... See
http://www.nfra.nl/~mag/hdf_evn.htm
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