25,156 research outputs found
Automatic channel switching device
Automatic channel switching device operates with all three triple modular redundant channels when there are no errors. When a failure occurs, channel and module switching isolate the failure to a specific channel. Since only one must operate correctly, reliability is increased
Chebyshev constants for the unit circle
It is proven that for any system of n points z_1, ..., z_n on the (complex)
unit circle, there exists another point z of norm 1, such that
Equality holds iff the point system is a
rotated copy of the nth unit roots.
Two proofs are presented: one uses a characterisation of equioscillating
rational functions, while the other is based on Bernstein's inequality.Comment: 11 page
Double-lepton polarizations in (B -> l^+ l^- gamma) decay
Double-lepton polarization asymmetries in the (B -> l^+ l^- gamma) decay are
calculated using the most general, model independent form of the effective
Hamiltonian including all possible forms of the interaction. The dependencies
of the asymmetries on new Wilson coefficients are investigated. The
detectability the averaged double-lepton polarization asymmetries at LHC is
also discussed.Comment: 20 pages, 7 PostScript figures, LaTeX formatte
The Form Factor in The Whole Kinematically Accessible Range
A systematic analysis is presented of the form factor in the whole range of momentum transfer , which would be useful to
analyzing the future data on decays and extracting .
With a modified QCD light cone sum rule (LCSR) approach, in which the
contributions cancel out from the twist 3 wavefunctions of meson, we
investigate in detail the behavior of at small and intermediate
and the nonperturbative quantity
is the decay constant of meson and
the strong coupling), whose numerical
result is used to study dependence of at large in
the single pole approximation. Based on these findings, a form factor model
from the best fit is formulated, which applies to the calculation on
in the whole kinematically accessible range. Also, a comparison is made with
the standard LCSR predictions.Comment: 11 pages, Latex, 1 eps figure, Final version to appear in Phys.Rev.
The effect of noise correlations on randomized benchmarking
Among the most popular and well studied quantum characterization,
verification and validation techniques is randomized benchmarking (RB), an
important statistical tool used to characterize the performance of physical
logic operations useful in quantum information processing. In this work we
provide a detailed mathematical treatment of the effect of temporal noise
correlations on the outcomes of RB protocols. We provide a fully analytic
framework capturing the accumulation of error in RB expressed in terms of a
three-dimensional random walk in "Pauli space." Using this framework we derive
the probability density function describing RB outcomes (averaged over noise)
for both Markovian and correlated errors, which we show is generally described
by a gamma distribution with shape and scale parameters depending on the
correlation structure. Long temporal correlations impart large nonvanishing
variance and skew in the distribution towards high-fidelity outcomes --
consistent with existing experimental data -- highlighting potential
finite-sampling pitfalls and the divergence of the mean RB outcome from
worst-case errors in the presence of noise correlations. We use the
Filter-transfer function formalism to reveal the underlying reason for these
differences in terms of effective coherent averaging of correlated errors in
certain random sequences. We conclude by commenting on the impact of these
calculations on the utility of single-metric approaches to quantum
characterization, verification, and validation.Comment: Updated and expanded to include full derivation. Related papers
available from http://www.physics.usyd.edu.au/~mbiercuk/Publications.htm
SCET sum rules for B->P and B->V transition form factors
We investigate sum rules for heavy-to-light transition form factors at large
recoil derived from correlation functions with interpolating currents for light
pseudoscalar or vector fields in soft-collinear effective theory (SCET). We
consider both, factorizable and non-factorizable contributions at leading power
in the Lambda/m_b expansion and to first order in the strong coupling constant
alpha_s, neglecting contributions from 3-particle distribution amplitudes in
the B-meson. We pay particular attention to various sources of parametric and
systematic uncertainties. We also discuss certain form factor ratios where part
of the hadronic uncertainties related to the B-meson distribution amplitude and
to logarithmically enhanced alpha_s corrections cancel.Comment: 27 pages, 19 figures, minor corrections, matches journal versio
Analysis of B-> \phi K Decays in QCD Factorization
We analyze the decay within the framework of QCD-improved
factorization. We found that although the twist-3 kaon distribution amplitude
dominates the spectator interactions, it will suppress the decay rates
slightly. The weak annihilation diagrams induced by penguin
operators, which are formally power-suppressed by order , are
chirally and logarithmically enhanced. Therefore, these annihilation
contributions are not subject to helicity suppression and can be sizable. The
predicted branching ratio of is in
the absence of annihilation contributions and it becomes
when annihilation effects are taken into
account. The prediction is consistent with CLEO and BaBar data but smaller than
the BELLE result.Comment: 13 pages, 3 figures. A major change for the presentation of
branching-ratio predictions. Experimental data are update
Experimental quantum verification in the presence of temporally correlated noise
Growth in the complexity and capabilities of quantum information hardware
mandates access to practical techniques for performance verification that
function under realistic laboratory conditions. Here we experimentally
characterise the impact of common temporally correlated noise processes on both
randomised benchmarking (RB) and gate-set tomography (GST). We study these
using an analytic toolkit based on a formalism mapping noise to errors for
arbitrary sequences of unitary operations. This analysis highlights the role of
sequence structure in enhancing or suppressing the sensitivity of quantum
verification protocols to either slowly or rapidly varying noise, which we
treat in the limiting cases of quasi-DC miscalibration and white noise power
spectra. We perform experiments with a single trapped Yb ion as a
qubit and inject engineered noise () to probe protocol
performance. Experiments on RB validate predictions that the distribution of
measured fidelities over sequences is described by a gamma distribution varying
between approximately Gaussian for rapidly varying noise, and a broad, highly
skewed distribution for the slowly varying case. Similarly we find a strong
gate set dependence of GST in the presence of correlated errors, leading to
significant deviations between estimated and calculated diamond distances in
the presence of correlated errors. Numerical simulations demonstrate
that expansion of the gate set to include negative rotations can suppress these
discrepancies and increase reported diamond distances by orders of magnitude
for the same error processes. Similar effects do not occur for correlated
or errors or rapidly varying noise processes,
highlighting the critical interplay of selected gate set and the gauge
optimisation process on the meaning of the reported diamond norm in correlated
noise environments.Comment: Expanded and updated analysis of GST, including detailed examination
of the role of gauge optimization in GST. Full GST data sets and
supplementary information available on request from the authors. Related
results available from
http://www.physics.usyd.edu.au/~mbiercuk/Publications.htm
Symmetries and Asymmetries of B -> K* mu+ mu- Decays in the Standard Model and Beyond
The rare decay B -> K* (-> K pi) mu+ mu- is regarded as one of the crucial
channels for B physics as the polarization of the K* allows a precise angular
reconstruction resulting in many observables that offer new important tests of
the Standard Model and its extensions. These angular observables can be
expressed in terms of CP-conserving and CP-violating quantities which we study
in terms of the full form factors calculated from QCD sum rules on the
light-cone, including QCD factorization corrections. We investigate all
observables in the context of the Standard Model and various New Physics
models, in particular the Littlest Higgs model with T-parity and various MSSM
scenarios, identifying those observables with small to moderate dependence on
hadronic quantities and large impact of New Physics. One important result of
our studies is that new CP-violating phases will produce clean signals in
CP-violating asymmetries. We also identify a number of correlations between
various observables which will allow a clear distinction between different New
Physics scenarios.Comment: 56 pages, 18 figures, 14 tables. v5: Missing factor in eqs. (3.31-32)
and fig. 6 corrected. Minor misprints in eq. (2.10) and table A corrected.
Conclusions unchange
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