759 research outputs found
Mutually Unbiased Bases, Generalized Spin Matrices and Separability
A collection of orthonormal bases for a complex dXd Hilbert space is called
mutually unbiased (MUB) if for any two vectors v and w from different bases the
square of the inner product equals 1/d: || ^{2}=1/d. The MUB problem is to
prove or disprove the the existence of a maximal set of d+1 bases. It has been
shown in [W. K. Wootters, B. D. Fields, Annals of Physics, 191, no. 2, 363-381,
(1989)] that such a collection exists if d is a power of a prime number p. We
revisit this problem and use dX d generalizations of the Pauli spin matrices to
give a constructive proof of this result. Specifically we give explicit
representations of commuting families of unitary matrices whose eigenvectors
solve the MUB problem. Additionally we give formulas from which the orthogonal
bases can be readily computed. We show how the techniques developed here
provide a natural way to analyze the separability of the bases. The techniques
used require properties of algebraic field extensions, and the relevant part of
that theory is included in an Appendix
Universally Decodable Matrices for Distributed Matrix-Vector Multiplication
Coded computation is an emerging research area that leverages concepts from
erasure coding to mitigate the effect of stragglers (slow nodes) in distributed
computation clusters, especially for matrix computation problems. In this work,
we present a class of distributed matrix-vector multiplication schemes that are
based on codes in the Rosenbloom-Tsfasman metric and universally decodable
matrices. Our schemes take into account the inherent computation order within a
worker node. In particular, they allow us to effectively leverage partial
computations performed by stragglers (a feature that many prior works lack). An
additional main contribution of our work is a companion matrix-based embedding
of these codes that allows us to obtain sparse and numerically stable schemes
for the problem at hand. Experimental results confirm the effectiveness of our
techniques.Comment: 6 pages, 1 figur
On the Exact Evaluation of Certain Instances of the Potts Partition Function by Quantum Computers
We present an efficient quantum algorithm for the exact evaluation of either
the fully ferromagnetic or anti-ferromagnetic q-state Potts partition function
Z for a family of graphs related to irreducible cyclic codes. This problem is
related to the evaluation of the Jones and Tutte polynomials. We consider the
connection between the weight enumerator polynomial from coding theory and Z
and exploit the fact that there exists a quantum algorithm for efficiently
estimating Gauss sums in order to obtain the weight enumerator for a certain
class of linear codes. In this way we demonstrate that for a certain class of
sparse graphs, which we call Irreducible Cyclic Cocycle Code (ICCC_\epsilon)
graphs, quantum computers provide a polynomial speed up in the difference
between the number of edges and vertices of the graph, and an exponential speed
up in q, over the best classical algorithms known to date
Quantum Block and Convolutional Codes from Self-orthogonal Product Codes
We present a construction of self-orthogonal codes using product codes. From
the resulting codes, one can construct both block quantum error-correcting
codes and quantum convolutional codes. We show that from the examples of
convolutional codes found, we can derive ordinary quantum error-correcting
codes using tail-biting with parameters [[42N,24N,3]]_2. While it is known that
the product construction cannot improve the rate in the classical case, we show
that this can happen for quantum codes: we show that a code [[15,7,3]]_2 is
obtained by the product of a code [[5,1,3]]_2 with a suitable code.Comment: 5 pages, paper presented at the 2005 IEEE International Symposium on
Information Theor
Theory of Finite Pseudoalgebras
Conformal algebras, recently introduced by Kac, encode an axiomatic
description of the singular part of the operator product expansion in conformal
field theory. The objective of this paper is to develop the theory of
``multi-dimensional'' analogues of conformal algebras. They are defined as Lie
algebras in a certain ``pseudotensor'' category instead of the category of
vector spaces. A pseudotensor category (as introduced by Lambek, and by
Beilinson and Drinfeld) is a category equipped with ``polylinear maps'' and a
way to compose them. This allows for the definition of Lie algebras,
representations, cohomology, etc. An instance of such a category can be
constructed starting from any cocommutative (or more generally,
quasitriangular) Hopf algebra . The Lie algebras in this category are called
Lie -pseudoalgebras.
The main result of this paper is the classification of all simple and all
semisimple Lie -pseudoalgebras which are finitely generated as -modules.
We also start developing the representation theory of Lie pseudoalgebras; in
particular, we prove analogues of the Lie, Engel, and Cartan-Jacobson Theorems.
We show that the cohomology theory of Lie pseudoalgebras describes extensions
and deformations and is closely related to Gelfand-Fuchs cohomology. Lie
pseudoalgebras are closely related to solutions of the classical Yang-Baxter
equation, to differential Lie algebras (introduced by Ritt), and to Hamiltonian
formalism in the theory of nonlinear evolution equations. As an application of
our results, we derive a classification of simple and semisimple linear Poisson
brackets in any finite number of indeterminates.Comment: 102 pages, 7 figures, AMS late
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