15,062 research outputs found
Entanglement, which-way measurements, and a quantum erasure
We present a didactical approach to the which-way experiment and the
counterintuitive effect of the quantum erasure for one-particle quantum
interferences. The fundamental concept of entanglement plays a central role and
highlights the complementarity between quantum interference and knowledge of
which path is followed by the particle.Comment: 5 pages, 4 figures; with some clarifications and added reference
Optimal Threshold-Based Multi-Trial Error/Erasure Decoding with the Guruswami-Sudan Algorithm
Traditionally, multi-trial error/erasure decoding of Reed-Solomon (RS) codes
is based on Bounded Minimum Distance (BMD) decoders with an erasure option.
Such decoders have error/erasure tradeoff factor L=2, which means that an error
is twice as expensive as an erasure in terms of the code's minimum distance.
The Guruswami-Sudan (GS) list decoder can be considered as state of the art in
algebraic decoding of RS codes. Besides an erasure option, it allows to adjust
L to values in the range 1<L<=2. Based on previous work, we provide formulae
which allow to optimally (in terms of residual codeword error probability)
exploit the erasure option of decoders with arbitrary L, if the decoder can be
used z>=1 times. We show that BMD decoders with z_BMD decoding trials can
result in lower residual codeword error probability than GS decoders with z_GS
trials, if z_BMD is only slightly larger than z_GS. This is of practical
interest since BMD decoders generally have lower computational complexity than
GS decoders.Comment: Accepted for the 2011 IEEE International Symposium on Information
Theory, St. Petersburg, Russia, July 31 - August 05, 2011. 5 pages, 2 figure
Optimal Thresholds for GMD Decoding with (L+1)/L-extended Bounded Distance Decoders
We investigate threshold-based multi-trial decoding of concatenated codes
with an inner Maximum-Likelihood decoder and an outer error/erasure
(L+1)/L-extended Bounded Distance decoder, i.e. a decoder which corrects e
errors and t erasures if e(L+1)/L + t <= d - 1, where d is the minimum distance
of the outer code and L is a positive integer. This is a generalization of
Forney's GMD decoding, which was considered only for L = 1, i.e. outer Bounded
Minimum Distance decoding. One important example for (L+1)/L-extended Bounded
Distance decoders is decoding of L-Interleaved Reed-Solomon codes. Our main
contribution is a threshold location formula, which allows to optimally erase
unreliable inner decoding results, for a given number of decoding trials and
parameter L. Thereby, the term optimal means that the residual codeword error
probability of the concatenated code is minimized. We give an estimation of
this probability for any number of decoding trials.Comment: Accepted for the 2010 IEEE International Symposium on Information
Theory, Austin, TX, USA, June 13 - 18, 2010. 5 pages, 2 figure
Coherent single atom shuttle between two Bose-Einstein condensates
We study an atomic quantum dot representing a single hyperfine "impurity"
atom which is coherently coupled to two well-separated Bose-Einstein
condensates, in the limit when the coupling between the dot and the condensates
dominates the inter-condensate tunneling coupling. It is demonstrated that the
quantum dot by itself can induce large-amplitude Josephson-like oscillations of
the particle imbalance between the condensates, which display a two-frequency
behavior. For noninteracting condensates, we provide an approximate solution to
the coupled nonlinear equations of motion which allows us to obtain these two
frequencies analytically.Comment: 4 pages of RevTex4, 4 figures; Rapid Communication in Physical Review
Thermal Quantum Fields without Cut-offs in 1+1 Space-time Dimensions
We construct interacting quantum fields in 1+1 dimensional Minkowski space,
representing neutral scalar bosons at positive temperature. Our work is based
on prior work by Klein and Landau and Hoegh-KrohnComment: 48 page
Motion by Stopping: Rectifying Brownian Motion of Non-spherical Particles
We show that Brownian motion is spatially not symmetric for mesoscopic
particles embedded in a fluid if the particle is not in thermal equilibrium and
its shape is not spherical. In view of applications on molecular motors in
biological cells, we sustain non-equilibrium by stopping a non-spherical
particle at periodic sites along a filament. Molecular dynamics simulations in
a Lennard-Jones fluid demonstrate that directed motion is possible without a
ratchet potential or temperature gradients if the asymmetric non-equilibrium
relaxation process is hindered by external stopping. Analytic calculations in
the ideal gas limit show that motion even against a fluid drift is possible and
that the direction of motion can be controlled by the shape of the particle,
which is completely characterized by tensorial Minkowski functionals.Comment: 11 pages, 5 figure
Exact Site Percolation Thresholds Using the Site-to-Bond and Star-Triangle Transformations
I construct a two-dimensional lattice on which the inhomogeneous site
percolation threshold is exactly calculable and use this result to find two
more lattices on which the site thresholds can be determined. The primary
lattice studied here, the ``martini lattice'', is a hexagonal lattice with
every second site transformed into a triangle. The site threshold of this
lattice is found to be , while the others have and
. This last solution suggests a possible approach to establishing
the bound for the hexagonal site threshold, . To derive these
results, I solve a correlated bond problem on the hexagonal lattice by use of
the star-triangle transformation and then, by a particular choice of
correlations, solve the site problem on the martini lattice.Comment: 12 pages, 10 figures. Submitted to Physical Review
- …