361 research outputs found
Nested Lattice Codes for Gaussian Relay Networks with Interference
In this paper, a class of relay networks is considered. We assume that, at a
node, outgoing channels to its neighbors are orthogonal, while incoming signals
from neighbors can interfere with each other. We are interested in the
multicast capacity of these networks. As a subclass, we first focus on Gaussian
relay networks with interference and find an achievable rate using a lattice
coding scheme. It is shown that there is a constant gap between our achievable
rate and the information theoretic cut-set bound. This is similar to the recent
result by Avestimehr, Diggavi, and Tse, who showed such an approximate
characterization of the capacity of general Gaussian relay networks. However,
our achievability uses a structured code instead of a random one. Using the
same idea used in the Gaussian case, we also consider linear finite-field
symmetric networks with interference and characterize the capacity using a
linear coding scheme.Comment: 23 pages, 5 figures, submitted to IEEE Transactions on Information
Theor
Correlated photon-pair generation in reverse-proton-exchange PPLN waveguides with integrated mode demultiplexer at 10 GHz clock
We report 10-ps correlated photon pair generation in periodically-poled
reverse-proton-exchange lithium niobate waveguides with integrated mode
demultiplexer at a wavelength of 1.5-um and a clock of 10 GHz. Using
superconducting single photon detectors, we observed a coincidence to
accidental count ratio (CAR) as high as 4000. The developed photon-pair source
may find broad application in quantum information systems as well as quantum
entanglement experiments.Comment: 6 pages, 4 figures, presented at 2007 CLEO conferenc
Single-photon detection timing jitter in a visible light photon counter
Visible light photon counters (VLPCs) offer many attractive features as
photon detectors, such as high quantum efficiency and photon number resolution.
We report measurements of the single-photon timing jitter in a VLPC, a critical
performance factor in a time-correlated single-photon counting measurement, in
a fiber-coupled closed-cycle cryocooler. The measured timing jitter is 240 ps
full-width-at-half-maximum at a wavelength of 550 nm, with a dark count rate of
25 000 counts per second. The timing jitter increases modestly at longer
wavelengths to 300 ps at 1000 nm, and increases substantially at lower bias
voltages as the quantum efficiency is reduced
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