1,334 research outputs found
Monte Carlo Simulations of the SU(2) Vacuum Structure
Lattice Monte Carlo simulations are performed for the SU(2) Yang Mills gauge
theory in the presence of an Abelian background with external sources to obtain
information on the effective potential. The goal is to investigate the lowest
Landau mode that, in the continuum one-loop effective potential, is the crucial
mode for instability. It is shown that also in the lattice formulation this
lowest Landau mode plays a very peculiar role, and it is important for the
understanding of the vacuum properties.Comment: 3 pages, to appear in the Proceedings of Lattice 93, preprint
BU-HEP-93-2
Electrical activity of carbon-hydrogen centers in Si
The electrical activity of Cs-H defects in Si has been investigated in a combined modeling and experimental study. High-resolution Laplace capacitance spectroscopy with the uniaxial stress technique has been used to measure the stress-energy tensor and the results are compared with theoretical modeling. At low temperatures, implanted H is trapped as a negative-U center with a donor level in the upper half of the gap. However, at higher temperatures, H migrates closer to the carbon impurity and the donor level falls, crossing the gap. At the same time, an acceptor level is introduced into the upper gap making the defect a positive-U center
An investigation into procedural (in)variance in the valuation of mortality risk reductions
This study investigates whether elicited preferences are affected by the presentation of mortality risks in a stated preference survey. We elicited willingness to pay for public risk reducing initiatives under three different but outcome equivalent presentation format. Results from a discrete choice experiment demonstrate that presentation format influences the valuation of mortality risk reductions, which to varying degrees depends on the respondent's level of concern and numeracy. Marginal willingness to pay for a risk reduction increases significantly when framed in terms of avoided fatalities compared to corresponding frequencies. Furthermore, we find that less numerate respondents are more influenced by the inclusion of the number of fatalities in the presentation format. The same pattern is observed for respondents who express a higher degree of concern for a traffic accident
Achievable rates for the Gaussian quantum channel
We study the properties of quantum stabilizer codes that embed a
finite-dimensional protected code space in an infinite-dimensional Hilbert
space. The stabilizer group of such a code is associated with a symplectically
integral lattice in the phase space of 2N canonical variables. From the
existence of symplectically integral lattices with suitable properties, we
infer a lower bound on the quantum capacity of the Gaussian quantum channel
that matches the one-shot coherent information optimized over Gaussian input
states.Comment: 12 pages, 4 eps figures, REVTe
On the Correlations Between Quantum Entanglement and q-Information Measures
In the present study we revisit the application of the -information
measures of R\'enyi's and of Tsallis' to the discussion of special
features of two qubits systems. More specifically, we study the correlations
between the -information measures and the entanglement of formation of a
general (pure or mixed) state describing a system of two qubits. The
analysis uses a Monte Carlo procedure involving the 15-dimensional 2-qubits
space of pure and mixed states, under the assumption that these states are
uniformly distributed according to the product measure recently introduced by
Zyczkowski {\it et al} [Phys. Rev. A {\bf 58} (1998) 883].Comment: 7 figures. Submitted for publicatio
The helium trimer with soft-core potentials
The helium trimer is studied using two- and three-body soft-core potentials.
Realistic helium-helium potentials present an extremely strong short-range
repulsion and support a single, very shallow, bound state. The description of
systems with more than two helium atoms is difficult due to the very large
cancellation between kinetic and potential energy. We analyze the possibility
of describing the three helium system in the ultracold regime using a gaussian
representation of a widely used realistic potential, the LM2M2 interaction.
However, in order to describe correctly the trimer ground state a three-body
force has to be added to the gaussian interaction. With this potential model
the two bound states of the trimer and the low energy scattering helium-dimer
phase shifts obtained with the LM2M2 potential are well reproduced.Comment: 15 pages, 3 figures, submitted to Few-Body System
Superconducting p-branes and Extremal Black Holes
In Einstein-Maxwell theory, magnetic flux lines are `expelled' from a black
hole as extremality is approached, in the sense that the component of the field
strength normal to the horizon goes to zero. Thus, extremal black holes are
found to exhibit the sort of `Meissner effect' which is characteristic of
superconducting media. We review some of the evidence for this effect, and do
present new evidence for it using recently found black hole solutions in string
theory and Kaluza-Klein theory. We also present some new solutions, which arise
naturally in string theory, which are non-superconducting extremal black holes.
We present a nice geometrical interpretation of these effects derived by
looking carefully at the higher dimensional configurations from which the lower
dimensional black hole solutions are obtained. We show that other extremal
solitonic objects in string theory (such as p-branes) can also display
superconducting properties. In particular, we argue that the relativistic
London equation will hold on the worldvolume of `light' superconducting
p-branes (which are embedded in flat space), and that minimally coupled zero
modes will propagate in the adS factor of the near-horizon geometries of
`heavy', or gravitating, superconducting p-branes.Comment: 22 pages, 2 figure
Optimal correction of concatenated fault-tolerant quantum codes
We present a method of concatenated quantum error correction in which
improved classical processing is used with existing quantum codes and
fault-tolerant circuits to more reliably correct errors. Rather than correcting
each level of a concatenated code independently, our method uses information
about the likelihood of errors having occurred at lower levels to maximize the
probability of correctly interpreting error syndromes. Results of simulations
of our method applied to the [[4,1,2]] subsystem code indicate that it can
correct a number of discrete errors up to half of the distance of the
concatenated code, which is optimal.Comment: 7 pages, 2 figures, published versio
The Case for Quantum Key Distribution
Quantum key distribution (QKD) promises secure key agreement by using quantum
mechanical systems. We argue that QKD will be an important part of future
cryptographic infrastructures. It can provide long-term confidentiality for
encrypted information without reliance on computational assumptions. Although
QKD still requires authentication to prevent man-in-the-middle attacks, it can
make use of either information-theoretically secure symmetric key
authentication or computationally secure public key authentication: even when
using public key authentication, we argue that QKD still offers stronger
security than classical key agreement.Comment: 12 pages, 1 figure; to appear in proceedings of QuantumComm 2009
Workshop on Quantum and Classical Information Security; version 2 minor
content revision
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