2,027 research outputs found
Optimum Quantum Error Recovery using Semidefinite Programming
Quantum error correction (QEC) is an essential element of physical quantum
information processing systems. Most QEC efforts focus on extending classical
error correction schemes to the quantum regime. The input to a noisy system is
embedded in a coded subspace, and error recovery is performed via an operation
designed to perfectly correct for a set of errors, presumably a large subset of
the physical noise process. In this paper, we examine the choice of recovery
operation. Rather than seeking perfect correction on a subset of errors, we
seek a recovery operation to maximize the entanglement fidelity for a given
input state and noise model. In this way, the recovery operation is optimum for
the given encoding and noise process. This optimization is shown to be
calculable via a semidefinite program (SDP), a well-established form of convex
optimization with efficient algorithms for its solution. The error recovery
operation may also be interpreted as a combining operation following a quantum
spreading channel, thus providing a quantum analogy to the classical diversity
combining operation.Comment: 7 pages, 3 figure
A New Class of Majoron-Emitting Double-Beta Decays
Motivated by the excess events that have recently been found near the
endpoints of the double beta decay spectra of several elements, we re-examine
models in which double beta decay can proceed through the neutrinoless emission
of massless Nambu-Goldstone bosons (majorons). Noting that models proposed to
date for this process must fine-tune either a scalar mass or a VEV to be less
than 10 keV, we introduce a new kind of majoron which avoids this difficulty by
carrying lepton number . We analyze in detail the requirements that
models of both the conventional and our new type must satisfy if they are to
account for the observed excess events. We find: (1) the electron sum-energy
spectrum can be used to distinguish the two classes of models from one another;
(2) the decay rate for the new models depends on different nuclear matrix
elements than for ordinary majorons; and (3) all models require a (pseudo)
Dirac neutrino, having a mass of a several hundred MeV, which mixes with
.Comment: 43 pages, 10 figures (included), [figure captions are now included
Dynamics of lattice spins as a model of arrhythmia
We consider evolution of initial disturbances in spatially extended systems
with autonomous rhythmic activity, such as the heart. We consider the case when
the activity is stable with respect to very smooth (changing little across the
medium) disturbances and construct lattice models for description of
not-so-smooth disturbances, in particular, topological defects; these models
are modifications of the diffusive XY model. We find that when the activity on
each lattice site is very rigid in maintaining its form, the topological
defects - vortices or spirals - nucleate a transition to a disordered,
turbulent state.Comment: 17 pages, revtex, 3 figure
The impact of inclusiveness on resilience in Temporary Multidisciplinary Organizations (TMO)
One of the enablers of organizational resilience is inclusiveness. Inclusiveness is the process of valuing, respecting and supporting members of an entity. Resilience in permanent organizations can be defined as the capability to respond to and prepare for disruption and thus, promote business continuity. On the other hand, resilience in Temporary Multidisciplinary Organizations (TMO) can be defined as the capability to respond to, prepare for and reduce the impact of disruptions caused by the drifting environment and complexity. A construction project can be viewed as a TMO. The time-limit and contract-focus of TMO challenges inclusiveness and hence makes its impact on resilience in TMO, unclear. Given the dynamic nature of TMOs (highly susceptible to disruptions), there is the need to identify the impact of inclusiveness, thus, the aim of this research. Using a case study approach (two case studies) and critical incident technique, it was identified that the TMO in which inclusiveness was actively promoted responded better to disruptions. This was enabled by project managers, directors and the project execution plan. The identified impact of inclusiveness in managing disruptions were; time and cost savings, innovation and quality enhancement. These findings contribute to debates on disruption management in TMOs (projects)
SMMC method for two-neutrino double beta decay
Shell Model Monte Carlo (SMMC) techniques are used to calculate two-neutrino
double beta decay matrix elements. We validate the approach against direct
diagonalization for Ca in the complete -shell using the KB3
interaction. The method is then applied to the decay of Ge in the
model space using a newly calculated realistic
interaction. Our result for the matrix element is MeV, in
agreement with the experimental value.Comment: 10 pages, 3 figures available at
http://www.krl.caltech.edu/preprints/MAP.htm
Shell Model Study of the Double Beta Decays of Ge, Se and Xe
The lifetimes for the double beta decays of Ge, Se and
Xe are calculated using very large shell model spaces. The two neutrino
matrix elements obtained are in good agreement with the present experimental
data. For eV we predict the following upper bounds to the
half-lives for the neutrinoless mode: , and . These results are the first from a new generation of Shell
Model calculations reaching O(10) dimensions
Comment on "Evidence for Neutrinoless Double Beta Decay"
We comment on the recent claim for the experimental observation of
neutrinoless double-beta decay. We discuss several limitations in the analysis
provided in that paper and conclude that there is no basis for the presented
claim.Comment: A comment written to Modern Physics Letters A. 4 pages, no figures.
Updated version, accepted for publicatio
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