1,721 research outputs found
Quantum MDS Codes over Small Fields
We consider quantum MDS (QMDS) codes for quantum systems of dimension
with lengths up to and minimum distances up to . We show how
starting from QMDS codes of length based on cyclic and constacyclic
codes, new QMDS codes can be obtained by shortening. We provide numerical
evidence for our conjecture that almost all admissible lengths, from a lower
bound on, are achievable by shortening. Some additional codes that
fill gaps in the list of achievable lengths are presented as well along with a
construction of a family of QMDS codes of length , where , that
appears to be new.Comment: 6 pages, 3 figure
On Hull-Variation Problem of Equivalent Linear Codes
The intersection () of a linear code and its Euclidean dual (Hermitian dual ) is called the Euclidean
(Hermitian) hull of this code. The construction of an entanglement-assisted
quantum code from a linear code over or depends
essentially on the Euclidean hull or the Hermitian hull of this code. Therefore
it is natural to consider the hull-variation problem when a linear code is transformed to an equivalent code . In this paper
we introduce the maximal hull dimension as an invariant of a linear code with
respect to the equivalent transformations. Then some basic properties of the
maximal hull dimension are studied. A general method to construct
hull-decreasing or hull-increasing equivalent linear codes is proposed. We
prove that for a nonnegative integer satisfying , a
linear self-dual code is equivalent to a linear -dimension hull
code. On the opposite direction we prove that a linear LCD code over satisfying and is equivalent to a linear
one-dimension hull code under a weak condition. Several new families of
negacyclic LCD codes and BCH LCD codes over are also constructed.
Our method can be applied to the generalized Reed-Solomon codes and the
generalized twisted Reed-Solomon codes to construct arbitrary dimension hull
MDS codes. Some new EAQEC codes including MDS and almost MDS
entanglement-assisted quantum codes are constructed. Many EAQEC codes over
small fields are constructed from optimal Hermitian self-dual codes.Comment: 33 pages, minor error correcte
Locally Encodable and Decodable Codes for Distributed Storage Systems
We consider the locality of encoding and decoding operations in distributed
storage systems (DSS), and propose a new class of codes, called locally
encodable and decodable codes (LEDC), that provides a higher degree of
operational locality compared to currently known codes. For a given locality
structure, we derive an upper bound on the global distance and demonstrate the
existence of an optimal LEDC for sufficiently large field size. In addition, we
also construct two families of optimal LEDC for fields with size linear in code
length.Comment: 7 page
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