13,051 research outputs found
Improvement of stabilizer based entanglement distillation protocols by encoding operators
This paper presents a method for enumerating all encoding operators in the
Clifford group for a given stabilizer. Furthermore, we classify encoding
operators into the equivalence classes such that EDPs (Entanglement
Distillation Protocol) constructed from encoding operators in the same
equivalence class have the same performance. By this classification, for a
given parameter, the number of candidates for good EDPs is significantly
reduced. As a result, we find the best EDP among EDPs constructed from [[4,2]]
stabilizer codes. This EDP has a better performance than previously known EDPs
over wide range of fidelity.Comment: 22 pages, 2 figures, In version 2, we enumerate all encoding
operators in the Clifford group, and fix the wrong classification of encoding
operators in version
DIRBE Minus 2MASS: Confirming the CIRB in 40 New Regions at 2.2 and 3.5 Microns
With the release of the 2MASS All-Sky Point Source Catalog, stellar fluxes
from 2MASS are used to remove the contribution due to Galactic stars from the
intensity measured by DIRBE in 40 new regions in the North and South Galactic
polar caps. After subtracting the interplanetary and Galactic foregrounds, a
consistent residual intensity of 14.69 +/- 4.49 kJy/sr at 2.2 microns is found.
Allowing for a constant calibration factor between the DIRBE 3.5 microns and
the 2MASS 2.2 microns fluxes, a similar analysis leaves a residual intensity of
15.62 +/- 3.34 kJy/sr at 3.5 microns. The intercepts of the DIRBE minus 2MASS
correlation at 1.25 microns show more scatter and are a smaller fraction of the
foreground, leading to a still weak limit on the CIRB of 8.88 +/- 6.26 kJy/sr
(1 sigma).Comment: 25 pages LaTeX, 10 figures, 5 tables; Version accepted by the ApJ.
Includes minor changes to the text including further discussion of zodiacal
light issues and the allowance for variable stars in computing uncertainties
in the stellar contribution to the DIRBE intensitie
Time evolution in linear response: Boltzmann equations and beyond
In this work a perturbative linear response analysis is performed for the
time evolution of the quasi-conserved charge of a scalar field. One can find
two regimes, one follows exponential damping, where the damping rate is shown
to come from quantum Boltzmann equations. The other regime (coming from
multiparticle cuts and products of them) decays as power law. The most
important, non-oscillating contribution in our model comes from a 4-particle
intermediate state and decays as 1/t^3. These results may have relevance for
instance in the context of lepton number violation in the Early Universe.Comment: 19 page
On Witten multiple zeta-functions associated with semisimple Lie algebras IV
In our previous work, we established the theory of multi-variable Witten
zeta-functions, which are called the zeta-functions of root systems. We have
already considered the cases of types , , , and . In
this paper, we consider the case of -type. We define certain analogues of
Bernoulli polynomials of -type and study the generating functions of them
to determine the coefficients of Witten's volume formulas of -type. Next
we consider the meromorphic continuation of the zeta-function of -type and
determine its possible singularities. Finally, by using our previous method, we
give explicit functional relations for them which include Witten's volume
formulas.Comment: 22 pag
Quantum error-correcting codes associated with graphs
We present a construction scheme for quantum error correcting codes. The
basic ingredients are a graph and a finite abelian group, from which the code
can explicitly be obtained. We prove necessary and sufficient conditions for
the graph such that the resulting code corrects a certain number of errors.
This allows a simple verification of the 1-error correcting property of
fivefold codes in any dimension. As new examples we construct a large class of
codes saturating the singleton bound, as well as a tenfold code detecting 3
errors.Comment: 8 pages revtex, 5 figure
Elastic Instability Triggered Pattern Formation
Recent experiments have exploited elastic instabilities in membranes to
create complex patterns. However, the rational design of such structures poses
many challenges, as they are products of nonlinear elastic behavior. We pose a
simple model for determining the orientational order of such patterns using
only linear elasticity theory which correctly predicts the outcomes of several
experiments. Each element of the pattern is modeled by a "dislocation dipole"
located at a point on a lattice, which then interacts elastically with all
other dipoles in the system. We explicitly consider a membrane with a square
lattice of circular holes under uniform compression and examine the changes in
morphology as it is allowed to relax in a specified direction.Comment: 15 pages, 7 figures, the full catastroph
Optimal cloning of mixed Gaussian states
We construct the optimal 1 to 2 cloning transformation for the family of
displaced thermal equilibrium states of a harmonic oscillator, with a fixed and
known temperature. The transformation is Gaussian and it is optimal with
respect to the figure of merit based on the joint output state and norm
distance. The proof of the result is based on the equivalence between the
optimal cloning problem and that of optimal amplification of Gaussian states
which is then reduced to an optimization problem for diagonal states of a
quantum oscillator. A key concept in finding the optimum is that of stochastic
ordering which plays a similar role in the purely classical problem of Gaussian
cloning. The result is then extended to the case of n to m cloning of mixed
Gaussian states.Comment: 8 pages, 1 figure; proof of general form of covariant amplifiers
adde
Spontaneous Hall effect in chiral p-wave superconductor
In a chiral superconductor with broken time-reversal symmetry a ``spontaneous
Hall effect'' may be observed. We analyze this phenomenon by taking into
account the surface properties of a chiral superconductor. We identify two main
contributions to the spontaneous Hall effect. One contribution originates from
the Bernoulli (or Lorentz) force from spontaneous currents running along the
surfaces of the superconductor. The other contribution has a topological origin
and is related to the intrinsic angular momentum of Cooper pairs. The latter
can be described in terms of a Chern-Simons-like term in the low-energy field
theory of the superconductor and has some similarities with the quantum Hall
effect. The spontaneous Hall effect in a chiral superconductor is, however,
non-universal. Our analysis is based on three approaches to the problem: a
self-consistent solution of the Bogoliubov-de Gennes equation, a generalized
Ginzburg-Landau theory, and a hydrodynamic formulation. All three methods
consistently lead to the same conclusion that the spontaneous Hall resistance
of a two-dimensional superconducting Hall bar is of order h/(e k_F\lambda)^2,
where k_F is the Fermi wave vector and \lambda is the London penetration depth;
the Hall resistance is substantially suppressed from a quantum unit of
resistance. Experimental issues in measuring this effect are briefly discussed.Comment: 22 pages including 12 figure
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