27,264 research outputs found
Entanglement distribution over the subsystems and its invariance
We study the entanglement dynamics of two qubits, each of which is embedded
into its local amplitude-damping reservoir, and the entanglement distribution
among all the bipartite subsystems including qubit-qubit, qubit-reservoir, and
reservoir-reservoir. It is found that the entanglement can be stably
distributed among all components, which is much different to the result
obtained under the Born-Markovian approximation by C. E. L\'{o}pez {\it et al.}
[Phys. Rev. Lett. \textbf{101}, 080503 (2008)], and particularly it also
satisfies an identity. Our unified treatment includes the previous results as
special cases. The result may give help to understand the physical nature of
entanglement under decoherence.Comment: 6 pages, 5 figure
Capacity scaling law by multiuser diversity in cognitive radio systems
This paper analyzes the multiuser diversity gain in a cognitive radio (CR)
system where secondary transmitters opportunistically utilize the spectrum
licensed to primary users only when it is not occupied by the primary users. To
protect the primary users from the interference caused by the missed detection
of primary transmissions in the secondary network, minimum average throughput
of the primary network is guaranteed by transmit power control at the secondary
transmitters. The traffic dynamics of a primary network are also considered in
our analysis. We derive the average achievable capacity of the secondary
network and analyze its asymptotic behaviors to characterize the multiuser
diversity gains in the CR system.Comment: 5 pages, 2 figures, ISIT2010 conferenc
Generating Many Majorana Modes via Periodic Driving: A Superconductor Model
Realizing Majorana modes (MMs) in condensed-matter systems is of vast
experimental and theoretical interests, and some signatures of MMs have been
measured already. To facilitate future experimental observations and to explore
further applications of MMs, generating many MMs at ease in an experimentally
accessible manner has become one important issue. This task is achieved here in
a one-dimensional -wave superconductor system with the nearest- and
next-nearest-neighbor interactions. In particular, a periodic modulation of
some system parameters can induce an effective long-range interaction (as
suggested by the Baker-Campbell-Hausdorff formula) and may recover
time-reversal symmetry already broken in undriven cases. By exploiting these
two independent mechanisms at once we have established a general method in
generating many Floquet MMs via periodic driving.Comment: 5 pages, 3 figures. To appear in Phys. Rev. B as a Rapid
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