2,714 research outputs found
Rapid adiabatic preparation of injective PEPS and Gibbs states
We propose a quantum algorithm for many-body state preparation. It is
especially suited for injective PEPS and thermal states of local commuting
Hamiltonians on a lattice. We show that for a uniform gap and sufficiently
smooth paths, an adiabatic runtime and circuit depth of
can be achieved for spins. This is an
almost exponential improvement over previous bounds. The total number of
elementary gates scales as . This is also faster
than the best known upper bound of on the mixing times of Monte Carlo
Markov chain algorithms for sampling classical systems in thermal equilibrium.Comment: 5 (+12) pages, 2 figure
Approximating Gibbs states of local Hamiltonians efficiently with PEPS
We analyze the error of approximating Gibbs states of local quantum spin
Hamiltonians on lattices with Projected Entangled Pair States (PEPS) as a
function of the bond dimension (), temperature (), and system
size (). First, we introduce a compression method in which the bond
dimension scales as if .
Second, building on the work of Hastings [Phys. Rev. B 73, 085115 (2006)], we
derive a polynomial scaling relation, .
This implies that the manifold of PEPS forms an efficient representation of
Gibbs states of local quantum Hamiltonians. From those bounds it also follows
that ground states can be approximated with whenever the
density of states only grows polynomially in the system size. All results hold
for any spatial dimension of the lattice.Comment: 12 pages, 1 figur
Kepler RR Lyrae stars: beyond period doubling
We examined the complete short cadence sample of Kepler RR Lyrae stars to
further investigate the recently discovered dynamical effects such as period
doubling and additional modes. Here we present the findings on four stars. V450
Lyr may be a non-classical double-mode RR Lyrae star pulsating in the
fundamental mode and the second overtone. In three cases we observe the
interaction of three different modes. Since the period ratios are close to
resonant values, we observe quasi-repetiting patterns in the pulsation cycles
in the stars. These findings support the mode-resonance explanations of the
Blazhko effect.Comment: 2 pages, 1 figure. Proceedings of the 301st IAU Symposium, Precision
Asteroseismology, August 2013, Wroc{\l}aw. V2: small corrections to the
wordin
Finite hadronization time and unitarity in quark recombination model
The effect of finite hadronization time is considered in the recombination
model, and it is shown that the hadron multiplicity turns out to be
proportional to the initial quark density and unitarity is conserved in the
model. The baryon to meson ratio increases rapidly with the initial quark
density due to competition among different channels.Comment: 4 pages in RevTeX, 3 eps figures, to appear in J. Phys.G as a lette
Nonlinear dynamical analysis of the Blazhko effect with the Kepler space telescope: the case of V783 Cyg
We present a detailed nonlinear dynamical investigation of the Blazhko
modulation of the Kepler RR Lyrae star V783 Cyg (KIC 5559631). We used
different techniques to produce modulation curves, including the determination
of amplitude maxima, the O-C diagram and the analytical function method. We
were able to fit the modulation curves with chaotic signals with the global
flow reconstruction method. However, when we investigated the effects of
instrumental and data processing artefacts, we found that the chaotic nature of
the modulation can not be proved because of the technical problems of data
stitching, detrending and sparse sampling. Moreover, we found that a
considerable part of the detected cycle-to-cycle variation of the modulation
may originate from these effects. According to our results, even the
four-year-long, unprecedented Kepler space photometry of V783 Cyg is too short
for a reliable nonlinear dynamical analysis aiming at the detection of chaos
from the Blazhko modulation. We estimate that two other stars could be suitable
for similar analysis in the Kepler sample and in the future TESS and PLATO may
provide additional candidates.Comment: 9 pages, 12 figures, accepted for publication in MNRA
On the interchange of alternating-amplitude pulsation cycles
We characterized the time intervals between the interchanges of the
alternating high- and low-amplitude extrema of three RV Tauri and three RR
Lyrae stars.Comment: 2 pages, Proceedings of the 301st IAU Symposium, Precision
Asteroseismology, August 201
Long time-scale behavior of the Blazhko effect from rectified Kepler data
In order to benefit from the 4-year unprecedented precision of the Kepler
data, we extracted light curves from the pixel photometric data of the Kepler
space telescope for 15 Blazhko RR Lyrae stars. For collecting all the flux from
a given target as accurately as possible, we defined tailor-made apertures for
each star and quarter. In some cases the aperture finding process yielded
sub-optimal result, because some flux have been lost even if the aperture
contains all available pixels around the star. This fact stresses the
importance of those methods that rely on the whole light curve instead of
focusing on the extrema (O-C diagrams and other amplitude independent methods).
We carried out detailed Fourier analysis of the light curves and the amplitude
independent O-C diagram. We found 12 (80%) multiperiodically modulated stars in
our sample. This ratio is much higher than previously found. Resonant coupling
between radial modes, a recent theory to explain of the Blazhko effect, allows
single, multiperiodic or even chaotic modulations. Among the stars with two
modulations we found three stars (V355 Lyr, V366 Lyr and V450 Lyr) where one of
the periods dominate in amplitude modulation, but the other period has larger
frequency modulation amplitude. The ratio between the primary and secondary
modulation periods is almost always very close to ratios of small integer
numbers. It may indicate the effect of undiscovered resonances. Furthermore, we
detected the excitation of the second radial overtone mode for three
stars where this feature was formerly unknown. Our data set comprises the
longest continuous, most precise observations of Blazhko RR Lyrae stars ever
published. These data which is made publicly available will be unprecedented
for years to come.Comment: 19 pages, 17 figures, accepted for publication in Astrophys. J.
Suppl. Rectified data are here: http://www.konkoly.hu/KIK/data.htm
Retention Behaviour of MNOS Memory Devices with Embedded Si or Ge Nanocrystals – Computer Simulation
The charge retention behaviour of MNOS structures with embedded Si or Ge nanocrystals are studied by computer simulation. It is obtained that the oxide thickness and the location of nanocrystlas affect the retention behaviour very strongly. The retention time changes from a few ms to several years.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3538
Differential freezeout and pion interferometry at RHIC from covariant transport theory
Puzzling discrepancies between recent pion interferometry data on Au+Au
reactions at s^1/2 = 130 and 200 AGeV from RHIC and predictions based on ideal
hydrodynamics are analyzed in terms of covariant parton transport theory. The
discrepancies of out and longitudinal radii are significantly reduced when the
finite opacity of the gluon plasma is taken into account.Comment: 4 pages, 3 EPS figures. Submitted to PR
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