1,504 research outputs found
Entanglement-assisted codeword stabilized quantum codes with imperfect ebits
Quantum error correcting codes (QECCs) in quantum communi- cation systems has
been known to exhibit improved performance with the use of error-free
entanglement bits (ebits). In practical situations, ebits inevitably suffer
from errors, and as a result, the error-correcting capability of the code is
diminished. Prior studies have proposed two different schemes as a solu- tion.
One uses only one QECC to correct errors on the receiver's side (i.e., Bob) and
on the sender's side (i.e., Alice). The other uses different QECCs on each
side. In this paper, we present a method to correct errors on both sides by
using single nonadditive Entanglement-assisted codeword stabilized quantum
error correcting code(EACWS QECC). We use the property that the number of
effective error patterns decreases as much as the number of ebits. This
property results in a greater number of logical codewords using the same number
of physical qubits
Flat bands in Network Superstructures of Atomic Chains
We investigate the origin of the ubiquitous existence of flat bands in the
network superstructures of atomic chains, where one-dimensional(1D) atomic
chains array periodically. While there can be many ways to connect those
chains, we consider two representative ways of linking them, the dot-type and
triangle-type links. Then, we construct a variety of superstructures, such as
the square, rectangular, and honeycomb network superstructures with dot-type
links and the honeycomb superstructure with triangle-type links. These links
provide the wavefunctions with an opportunity to have destructive interference,
which stabilizes the compact localized state(CLS). The CLS is a localized
eigenstate whose amplitudes are finite only inside a finite region and
guarantees the existence of a flat band. In the network superstructures, there
exist multiple flat bands proportional to the number of atoms of each chain,
and the corresponding eigenenergies can be found from the stability condition
of the compact localized state. Finally, we demonstrate that the finite
bandwidth of the nearly flat bands of the network superstructures arising from
the next-nearest-neighbor hopping processes can be suppressed by increasing the
length of the chains consisting of the superstructures.Comment: 8pages, 4figure
Progressive Processing of Continuous Range Queries in Hierarchical Wireless Sensor Networks
In this paper, we study the problem of processing continuous range queries in
a hierarchical wireless sensor network. Contrasted with the traditional
approach of building networks in a "flat" structure using sensor devices of the
same capability, the hierarchical approach deploys devices of higher capability
in a higher tier, i.e., a tier closer to the server. While query processing in
flat sensor networks has been widely studied, the study on query processing in
hierarchical sensor networks has been inadequate. In wireless sensor networks,
the main costs that should be considered are the energy for sending data and
the storage for storing queries. There is a trade-off between these two costs.
Based on this, we first propose a progressive processing method that
effectively processes a large number of continuous range queries in
hierarchical sensor networks. The proposed method uses the query merging
technique proposed by Xiang et al. as the basis and additionally considers the
trade-off between the two costs. More specifically, it works toward reducing
the storage cost at lower-tier nodes by merging more queries, and toward
reducing the energy cost at higher-tier nodes by merging fewer queries (thereby
reducing "false alarms"). We then present how to build a hierarchical sensor
network that is optimal with respect to the weighted sum of the two costs. It
allows for a cost-based systematic control of the trade-off based on the
relative importance between the storage and energy in a given network
environment and application. Experimental results show that the proposed method
achieves a near-optimal control between the storage and energy and reduces the
cost by 0.989~84.995 times compared with the cost achieved using the flat
(i.e., non-hierarchical) setup as in the work by Xiang et al.Comment: 41 pages, 20 figure
Entanglement-assisted codeword stabilized quantum codes
Entangled qubit can increase the capacity of quantum error correcting codes
based on stabilizer codes. In addition, by using entanglement quantum
stabilizer codes can be construct from classical linear codes that do not
satisfy the dual-containing constraint. We show that it is possible to
construct both additive and non-additive quantum codes using the codeword
stabilized quantum code framework. Nonadditive codes may offer improved
performance over the more common sta- bilizer codes. Like other
entanglement-assisted codes, the encoding procedure acts only the qubits on
Alice's side, and only these qubits are assumed to pass through the channel.
However, errors the codeword stabilized quantum code framework gives rise to
effective Z errors on Bob side. We use this scheme to construct new
entanglement-assisted non-additive quantum codes, in particular, ((5,16,2;1))
and ((7,4,5;4)) codes
- …