36,314 research outputs found
Cooperative Relay Broadcast Channels
The capacity regions are investigated for two relay broadcast channels
(RBCs), where relay links are incorporated into standard two-user broadcast
channels to support user cooperation. In the first channel, the Partially
Cooperative Relay Broadcast Channel, only one user in the system can act as a
relay and transmit to the other user through a relay link. An achievable rate
region is derived based on the relay using the decode-and-forward scheme. An
outer bound on the capacity region is derived and is shown to be tighter than
the cut-set bound. For the special case where the Partially Cooperative RBC is
degraded, the achievable rate region is shown to be tight and provides the
capacity region. Gaussian Partially Cooperative RBCs and Partially Cooperative
RBCs with feedback are further studied. In the second channel model being
studied in the paper, the Fully Cooperative Relay Broadcast Channel, both users
can act as relay nodes and transmit to each other through relay links. This is
a more general model than the Partially Cooperative RBC. All the results for
Partially Cooperative RBCs are correspondingly generalized to the Fully
Cooperative RBCs. It is further shown that the AWGN Fully Cooperative RBC has a
larger achievable rate region than the AWGN Partially Cooperative RBC. The
results illustrate that relaying and user cooperation are powerful techniques
in improving the capacity of broadcast channels.Comment: Submitted to the IEEE Transactions on Information Theory, July 200
Optimized Entanglement Purification
We investigate novel protocols for entanglement purification of qubit Bell
pairs. Employing genetic algorithms for the design of the purification circuit,
we obtain shorter circuits achieving higher success rates and better final
fidelities than what is currently available in the literature. We provide a
software tool for analytical and numerical study of the generated purification
circuits, under customizable error models. These new purification protocols
pave the way to practical implementations of modular quantum computers and
quantum repeaters. Our approach is particularly attentive to the effects of
finite resources and imperfect local operations - phenomena neglected in the
usual asymptotic approach to the problem. The choice of the building blocks
permitted in the construction of the circuits is based on a thorough
enumeration of the local Clifford operations that act as permutations on the
basis of Bell states
Visualization of Dimensional Effects in Collective Excitations of Optically Trapped Quasi-Two-Dimensional Bose Gases
We analyze the macroscopic dynamics of a Bose gas axially confined in an
optical lattice with a superimposed harmonic trap, taking into account weak
tunneling effect. Our results show that upon transition to the
quasi-two-dimensional (2D) regime of the trapped gas, the 3D equation of state
and equilibrium density profile acquire corrections from 2D many-body effects.
The corresponding frequency shift in the transverse breathing mode is
accessible within current facilities, suggesting a direct observation of
dimensional effects. Comparisons with other relevant effects are also
presented.Comment: 4 pages, 1 figur
Estimates for X(4350) Decays from the Effective Lagrangian Approach
The strong and electromagnetic decays of with quantum numbers and have been studied by using the effective Lagrangian
approach. The coupling constant between and
is determined with the help of the compositeness condition which means that
is a bound state of . Other coupling
constants applied in the calculation are determined phenomenologically. Our
numerical results show that, using the present data within the present model,
the possibility that is a molecule can not
be ruled out.Comment: 15 pages, 4 eps figure
- β¦