103 research outputs found
Intrinsic Decoherence Dynamics in Smooth Hamiltonian Systems: Quantum-classical Correspondence
A direct classical analog of the quantum dynamics of intrinsic decoherence in
Hamiltonian systems, characterized by the time dependence of the linear entropy
of the reduced density operator, is introduced. The similarities and
differences between the classical and quantum decoherence dynamics of an
initial quantum state are exposed using both analytical and computational
results. In particular, the classicality of early-time intrinsic decoherence
dynamics is explored analytically using a second-order perturbative treatment,
and an interesting connection between decoherence rates and the stability
nature of classical trajectories is revealed in a simple approximate classical
theory of intrinsic decoherence dynamics. The results offer new insights into
decoherence, dynamics of quantum entanglement, and quantum chaos.Comment: 12 pages, 7 figures, to appear in Physical Review
Suppression of decoherence in quantum registers by entanglement with a nonequilibrium environment
It is shown that a nonequilibrium environment can be instrumental in
suppressing decoherence between distinct decoherence free subspaces in quantum
registers. The effect is found in the framework of exact coherent-product
solutions for model registers decohering in a bath of degenerate harmonic
modes, through couplings linear in bath coordinates. These solutions represent
a natural nonequilibrium extension of the standard solution for a decoupled
initial register state and a thermal environment. Under appropriate conditions,
the corresponding reduced register distribution can propagate in an unperturbed
manner, even in the presence of entanglement between states belonging to
distinct decoherence free subspaces, and despite persistent bath entanglement.
As a byproduct, we also obtain a refined picture of coherence dynamics under
bang-bang decoherence control. In particular, it is shown that each
radio-frequency pulse in a typical bang-bang cycle induces a revival of
coherence, and that these revivals are exploited in a natural way by the
time-symmetrized version of the bang-bang protocol.Comment: RevTex3, 26 pgs., 2 figs.. This seriously expanded version accepted
by Phys.Rev.A. No fundamentally new content, but rewritten introduction to
problem, self-contained introduction of thermal coherent-product states in
standard operator formalism, examples of zero-temperature decoherence free
Davydov states. Also fixed a typo that propagated into an interpretational
blunder in old Sec.3 [fortunately of no consequence
One-dimensional quantum walk with unitary noise
The effect of unitary noise on the discrete one-dimensional quantum walk is studied using computer simulations. For the noiseless quantum walk, starting at the origin (n=0) at time t=0, the position distribution P-t(n) at time t is very different from the Gaussian distribution obtained for the classical random walk. Furthermore, its standard deviation, sigma(t) scales as sigma(t)similar tot, unlike the classical random walk for which sigma(t)similar toroott. It is shown that when the quantum walk is exposed to unitary noise, it exhibits a crossover from quantum behavior for short times to classical-like behavior for long times. The crossover time is found to be Tsimilar toalpha(-2), where alpha is the standard deviation of the noise
Near-IR Atlas of S0-Sa galaxies (NIRS0S)
An atlas of Ks-band images of 206 early-type galaxies is presented, including
160 S0-S0/a galaxies, 12 ellipticals, and 33 Sa galaxies. A majority of the
Atlas galaxies belong to a magnitude-limited (mB<12.5 mag) sample of 185 NIRS0S
(Near-IR S0 galaxy Survey) galaxies. To assure that mis-classified S0s are not
omitted, 25 ellipticals from RC3 classified as S0s in the Carnegie Atlas were
included in the sample. The images are 2-3 mag deeper than 2MASS images. Both
visual and photometric classifications are made. Special attention is paid to
the classification of lenses, coded in a systematic manner. A new lens-type,
called a 'barlens', is introduced. Also, boxy/peanut/x-shaped structures are
identified in many barred galaxies, even-though the galaxies are not seen in
edge-on view, indicating that vertical thickening is not enough to explain
them. Multiple lenses appear in 25% of the Atlas galaxies, which is a challenge
to the hierarchical evolutionary picture of galaxies. Such models need to
explain how the lenses were formed and survived in multiple merger events that
galaxies may have suffered during their lifetimes. Following the early
suggestion by van den Bergh, candidates of S0c galaxies are shown, which
galaxies are expected to be former Sc-type spirals stripped out of gas.Comment: 67 pages (include 16 figures and 6 tables). Accepted to MNRAS 2011
June 1
D* Production in Deep Inelastic Scattering at HERA
This paper presents measurements of D^{*\pm} production in deep inelastic
scattering from collisions between 27.5 GeV positrons and 820 GeV protons. The
data have been taken with the ZEUS detector at HERA. The decay channel
(+ c.c.) has been used in the study. The
cross section for inclusive D^{*\pm} production with
and is 5.3 \pms 1.0 \pms 0.8 nb in the kinematic region
{ GeV and }. Differential cross
sections as functions of p_T(D^{*\pm}), and are
compared with next-to-leading order QCD calculations based on the photon-gluon
fusion production mechanism. After an extrapolation of the cross section to the
full kinematic region in p_T(D^{*\pm}) and (D^{*\pm}), the charm
contribution to the proton structure function is
determined for Bjorken between 2 10 and 5 10.Comment: 17 pages including 4 figure
Observation of Scaling Violations in Scaled Momentum Distributions at HERA
Charged particle production has been measured in deep inelastic scattering
(DIS) events over a large range of and using the ZEUS detector. The
evolution of the scaled momentum, , with in the range 10 to 1280
, has been investigated in the current fragmentation region of the Breit
frame. The results show clear evidence, in a single experiment, for scaling
violations in scaled momenta as a function of .Comment: 21 pages including 4 figures, to be published in Physics Letters B.
Two references adde
Observation of hard scattering in photoproduction events with a large rapidity gap at HERA
Events with a large rapidity gap and total transverse energy greater than 5
GeV have been observed in quasi-real photoproduction at HERA with the ZEUS
detector. The distribution of these events as a function of the
centre of mass energy is consistent with diffractive scattering. For total
transverse energies above 12 GeV, the hadronic final states show predominantly
a two-jet structure with each jet having a transverse energy greater than 4
GeV. For the two-jet events, little energy flow is found outside the jets. This
observation is consistent with the hard scattering of a quasi-real photon with
a colourless object in the proton.Comment: 19 pages, latex, 4 figures appended as uuencoded fil
Weak Lensing and Dark Energy
We study the power of upcoming weak lensing surveys to probe dark energy.
Dark energy modifies the distance-redshift relation as well as the matter power
spectrum, both of which affect the weak lensing convergence power spectrum.
Some dark-energy models predict additional clustering on very large scales, but
this probably cannot be detected by weak lensing alone due to cosmic variance.
With reasonable prior information on other cosmological parameters, we find
that a survey covering 1000 sq. deg. down to a limiting magnitude of R=27 can
impose constraints comparable to those expected from upcoming type Ia supernova
and number-count surveys. This result, however, is contingent on the control of
both observational and theoretical systematics. Concentrating on the latter, we
find that the {\it nonlinear} power spectrum of matter perturbations and the
redshift distribution of source galaxies both need to be determined accurately
in order for weak lensing to achieve its full potential. Finally, we discuss
the sensitivity of the three-point statistics to dark energy.Comment: 16 pages, revtex. Peacock-Dodds PS used for all w, which weakens the
constraints. Tomography sec. expanded, estimate included of how well
systematics need to be controlle
Separating the Early Universe from the Late Universe: cosmological parameter estimation beyond the black box
We present a method for measuring the cosmic matter budget without
assumptions about speculative Early Universe physics, and for measuring the
primordial power spectrum P*(k) non-parametrically, either by combining CMB and
LSS information or by using CMB polarization. Our method complements currently
fashionable ``black box'' cosmological parameter analysis, constraining
cosmological models in a more physically intuitive fashion by mapping
measurements of CMB, weak lensing and cluster abundance into k-space, where
they can be directly compared with each other and with galaxy and Lyman alpha
forest clustering. Including the new CBI results, we find that CMB measurements
of P(k) overlap with those from 2dF galaxy clustering by over an order of
magnitude in scale, and even overlap with weak lensing measurements. We
describe how our approach can be used to raise the ambition level beyond
cosmological parameter fitting as data improves, testing rather than assuming
the underlying physics.Comment: Replaced to match accepted PRD version. Refs added. Combined CMB data
and window functions at http://www.hep.upenn.edu/~max/pwindows.html or from
[email protected]. 18 figs, 19 journal page
The last stand before MAP: cosmological parameters from lensing, CMB and galaxy clustering
Cosmic shear measurements have now improved to the point where they deserve
to be treated on par with CMB and galaxy clustering data for cosmological
parameter analysis, using the full measured aperture mass variance curve rather
than a mere phenomenological parametrization thereof. We perform a detailed
9-parameter analysis of recent lensing (RCS), CMB (up to Archeops) and galaxy
clustering (2dF) data, both separately and jointly. CMB and 2dF data are
consistent with a simple flat adiabatic scale-invariant model with
Omega_Lambda=0.72+/-0.09, omega_cdm=0.115+/- 0.013, omega_b=0.024+/-0.003, and
a hint of reionization around z~8. Lensing helps further tighten these
constraints, but reveals tension regarding the power spectrum normalization:
including the RCS survey results raises sigma8 significantly and forces other
parameters to uncomfortable values. Indeed, sigma8 is emerging as the currently
most controversial cosmological parameter, and we discuss possible resolutions
of this sigma8 problem. We also comment on the disturbing fact that many recent
analyses (including this one) obtain error bars smaller than the Fisher matrix
bound. We produce a CMB power spectrum combining all existing experiments, and
using it for a "MAP versus world" comparison next month will provide a powerful
test of how realistic the error estimates have been in the cosmology community.Comment: Added references and Fisher error discussion. Combined CMB data,
window and covariance matrix for January "MAP vs World" contest at
http://www.hep.upenn.edu/~max/cmblsslens.html or from [email protected]
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