23,894 research outputs found
Query-Efficient Locally Decodable Codes of Subexponential Length
We develop the algebraic theory behind the constructions of Yekhanin (2008)
and Efremenko (2009), in an attempt to understand the ``algebraic niceness''
phenomenon in . We show that every integer ,
where , and are prime, possesses the same good algebraic property as
that allows savings in query complexity. We identify 50 numbers of this
form by computer search, which together with 511, are then applied to gain
improvements on query complexity via Itoh and Suzuki's composition method. More
precisely, we construct a -query LDC for every positive
integer and a -query
LDC for every integer , both of length , improving the
queries used by Efremenko (2009) and queries used by Itoh and
Suzuki (2010).
We also obtain new efficient private information retrieval (PIR) schemes from
the new query-efficient LDCs.Comment: to appear in Computational Complexit
An Efficient Method for Realizing Contractions of Access Structures in Cloud Storage
In single-cloud storage, ciphertext-policy attribute-based encryption
(CP-ABE) allows one to encrypt any data under an access structure to a cloud
server, specifying what attributes are required to decrypt. In multi-cloud
storage, a secret sharing scheme (SSS) allows one to split any data into
multiple shares, one to a single server, and specify which subset of the
servers are able to recover the data. It is an interesting problem to remove
some attributes/servers but still enable the remaining attributes/servers in
every authorized set to recover the data. The problem is related to the
contraction problem of access structures for SSSs. In this paper, we propose a
method that can efficiently transform a given SSS for an access structure to
SSSs for contractions of the access structure. We show its applications in
solving the attribute removal problem in the CP-ABE based single-cloud storage
and the data relocating problem in multi-cloud storage. Our method results in
solutions that require either less server storage or even no additional server
storage.Comment: IEEE Transactions on Services Computin
One-way cloak based on nonreciprocal photonic crystal
We propose a physical concept of non-reciprocal transformation optics, by which a one-way invisible cloak is designed. The one-way invisible cloak is made of a coordinate-transformed nonreciprocal photonic crystal, showing a perfect cloaking for wave incident from one direction but acting as a perfect reflector for wave from the counter direction. The proposed design shows a high promise of applications in military, as protecting the own information to be detected but efficiently grabbing the information from the “enemy” side
Probing Half-odd Topological Number with Cold Atoms in a Non-Abelian Optical Lattice
We propose an experimental scheme to probe the contribution of a single Dirac
cone to the Hall conductivity as half-odd topological number sequence. In our
scheme, the quantum anomalous Hall effect as in graphene is simulated with cold
atoms trapped in an optical lattice and subjected to a laser-induced
non-Abelian gauge field. By tuning the laser intensity to change the gauge
flux, the energies of the four Dirac points in the first Brillouin zone are
shifted with each other and the contribution of the single Dirac cone to the
total atomic Hall conductivity is manifested. We also show such manifestation
can be experimentally probed with atomic density profile measurements.Comment: 5 pages, 3 figure
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