36,783 research outputs found
Soft-pulse dynamical decoupling in a cavity
Dynamical decoupling is a coherent control technique where the intrinsic and
extrinsic couplings of a quantum system are effectively averaged out by
application of specially designed driving fields (refocusing pulse sequences).
This entails pumping energy into the system, which can be especially dangerous
when it has sharp spectral features like a cavity mode close to resonance. In
this work we show that such an effect can be avoided with properly constructed
refocusing sequences. To this end we construct the average Hamiltonian
expansion for the system evolution operator associated with a single ``soft''
pi-pulse. To second order in the pulse duration, we characterize a symmetric
pulse shape by three parameters, two of which can be turned to zero by shaping.
We express the effective Hamiltonians for several pulse sequences in terms of
these parameters, and use the results to analyze the structure of error
operators for controlled Jaynes-Cummings Hamiltonian. When errors are cancelled
to second order, numerical simulations show excellent qubit fidelity with
strongly-suppressed oscillator heating.Comment: 9pages, 5eps figure
Microscopic calculation of the phonon dynamics of SrRuO compared with LaCuO
The phonon dynamics of the low-temperature superconductor SrRuO
is calculated quantitatively in linear response theory and compared with the
structurally isomorphic high-temperature superconductor LaCuO. Our
calculation corrects for a typical deficit of LDA-based calculations which
always predict a too large electronic -dispersion insufficient to
describe the c-axis response in the real materials. With a more realistic
computation of the electronic band structure the frequency and wavevector
dependent irreducible polarization part of the density response function is
determined and used for adiabatic and nonadiabatic phonon calculations. Our
analysis for SrRuO reveals important differences from the lattice
dynamics of - and -doped cuprates. Consistent with experimental evidence
from inelastic neutron scattering the anomalous doping related softening of the
strongly coupling high-frequency oxygen bond-stretching modes (OBSM) which is
generic for the cuprate superconductors is largely suppressed or completely
absent, respectively, depending on the actual value of the on-site Coulomb
repulsion of the Ru4d orbitals. Also the presence of a characteristic
-mode with a very steep dispersion coupling strongly with the
electrons is missing in SrRuO. Moreover, we evaluate the
possibility of a phonon-plasmon scenario for SrRuO which has been
shown recently to be realistic for LaCuO. In contrast to
LaCuO in SrRuO the very low lying plasmons are
overdamped along the c-axis.Comment: 30 pages, 16 figures, 4 tables, 33 reference
A proof of factorization for B -> D pi
We prove that the matrix elements of four fermion operators mediating the
decay B^0 -> D^+ \pi^- and B^- -> D^0 \pi^- factor into the product of a form
factor describing the B -> D transition and a convolution of a short distance
coefficient with the nonperturbative pion light-cone wave function. This is
shown to all orders in alpha_s, up to corrections suppressed by factors of
1/mb, 1/mc, and 1/E_pi. It is not necessary to assume that the pion state is
dominated by the q-qbar Fock state.Comment: 4 pages, 3 figs, PRL versio
Nonsequential Double Recombination in Intense Laser Fields
A second plateau in the harmonic spectra of laser-driven two-electron atoms
is observed both in the numerical solution of a low-dimensional model helium
atom and using an extended strong field approximation. It is shown that the
harmonics well beyond the usual cut-off are due to the simultaneous
recombination of the two electrons, which were emitted during different,
previous half-cycles. The new cut-off is explained in terms of classical
trajectories. Classical predictions and the time-frequency analysis of the ab
initio quantum results are in excellent agreement. The mechanism corresponds to
the inverse single photon double ionization process in the presence of a (low
frequency) laser field.Comment: 4 pages, RevTeX, v2 with an extended strong field approximation
treatment of the process; instead, v1 describes an attosecond control scheme
to enhance the proces
Soft-Collinear Messengers: A New Mode in Soft-Collinear Effective Theory
It is argued that soft-collinear effective theory for processes involving
both soft and collinear partons, such as exclusive B-meson decays, should
include a new mode in addition to soft and collinear fields. These
"soft-collinear messengers" can interact with both soft and collinear particles
without taking them far off-shell. They thus can communicate between the soft
and collinear sectors of the theory. The relevance of the new mode is
demonstrated with an explicit example, and the formalism incorporating the
corresponding quark and gluon fields into the effective Lagrangian is
developed.Comment: 22 pages, 5 figures. Extended Section 6, clarifying the relevance of
different types of soft-collinear interaction
Phase diagram for morphological transitions of wetting films on chemically structured substrates
Using an interface displacement model we calculate the shapes of thin
liquidlike films adsorbed on flat substrates containing a chemical stripe. We
determine the entire phase diagram of morphological phase transitions in these
films as function of temperature, undersaturation, and stripe widthComment: 15 pages, RevTeX, 7 Figure
Runtime Verification of Temporal Properties over Out-of-order Data Streams
We present a monitoring approach for verifying systems at runtime. Our
approach targets systems whose components communicate with the monitors over
unreliable channels, where messages can be delayed or lost. In contrast to
prior works, whose property specification languages are limited to
propositional temporal logics, our approach handles an extension of the
real-time logic MTL with freeze quantifiers for reasoning about data values. We
present its underlying theory based on a new three-valued semantics that is
well suited to soundly and completely reason online about event streams in the
presence of message delay or loss. We also evaluate our approach
experimentally. Our prototype implementation processes hundreds of events per
second in settings where messages are received out of order.Comment: long version of the CAV 2017 pape
Phase Transitions in a Two-Component Site-Bond Percolation Model
A method to treat a N-component percolation model as effective one component
model is presented by introducing a scaled control variable . In Monte
Carlo simulations on , , and simple cubic
lattices the percolation threshold in terms of is determined for N=2.
Phase transitions are reported in two limits for the bond existence
probabilities and . In the same limits, empirical formulas
for the percolation threshold as function of one
component-concentration, , are proposed. In the limit a new
site percolation threshold, , is reported.Comment: RevTeX, 5 pages, 5 eps-figure
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