640 research outputs found
Green's functions technique for calculating the emission spectrum in a quantum dot-cavity system
We introduce the Green's functions technique as an alternative theory to the
quantum regression theorem formalism for calculating the two-time correlation
functions in open quantum systems. In particular, we investigate the potential
of this theoretical approach by its application to compute the emission
spectrum of a dissipative system composed by a single quantum dot inside of a
semiconductor cavity. We also describe a simple algorithm based on the Green's
functions technique for calculating the emission spectrum of the quantum dot as
well as of the cavity which can easily be implemented in any numerical linear
algebra package. We find that the Green's functions technique demonstrates a
better accuracy and efficiency in the calculation of the emission spectrum and
it allows to overcome the inherent theoretical difficulties associated to the
direct application of the quantum regression theorem approach
Degraded Broadcast Channel with Side Information, Confidential Messages and Noiseless Feedback
In this paper, first, we investigate the model of degraded broadcast channel
with side information and confidential messages. This work is from Steinberg's
work on the degraded broadcast channel with causal and noncausal side
information, and Csiszr-K\"{o}rner's work on broadcast channel with
confidential messages. Inner and outer bounds on the capacity-equivocation
regions are provided for the noncausal and causal cases. Superposition coding
and double-binning technique are used in the corresponding achievability
proofs.
Then, we investigate the degraded broadcast channel with side information,
confidential messages and noiseless feedback. The noiseless feedback is from
the non-degraded receiver to the channel encoder. Inner and outer bounds on the
capacity-equivocation region are provided for the noncausal case, and the
capacity-equivocation region is determined for the causal case. Compared with
the model without feedback, we find that the noiseless feedback helps to
enlarge the inner bounds for both causal and noncausal cases. In the
achievability proof of the feedback model, the noiseless feedback is used as a
secret key shared by the non-degraded receiver and the transmitter, and
therefore, the code construction for the feedback model is a combination of
superposition coding, Gel'fand-Pinsker's binning, block Markov coding and
Ahlswede-Cai's secret key on the feedback system.Comment: Part of this paper has been accepted by ISIT2012, and this paper is
submitted to IEEE Transactions on Information Theor
Characterization of dynamical regimes and entanglement sudden death in a microcavity quantum - dot system
The relation between the dynamical regimes (weak and strong coupling) and
entanglement for a dissipative quantum - dot microcavity system is studied. In
the framework of a phenomenological temperature model an analysis in both,
temporal (population dynamics) and frequency domain (photoluminescence) is
carried out in order to identify the associated dynamical behavior. The Wigner
function and concurrence are employed to quantify the entanglement in each
regime. We find that sudden death of entanglement is a typical characteristic
of the strong coupling regime.Comment: To appear in Journal of Physics: Condensed Matte
Road Network Deterioration Monitoring Using Aerial Images and Computer Vision
Road maintenance is an essential process for guaranteeing the quality of
transportation in any city. A crucial step towards effective road maintenance
is the ability to update the inventory of the road network. We present a proof
of concept of a protocol for maintaining said inventory based on the use of
unmanned aerial vehicles to quickly collect images which are processed by a
computer vision program that automatically identifies potholes and their
severity. Our protocol aims to provide information to local governments to
prioritise the road network maintenance budget, and to be able to detect early
stages of road deterioration so as to minimise maintenance expenditure.Comment: 5 pages, 4 figure
Interleaving and nulling to combat narrow-band interference in PLC standard technologies PLC G3 and PRIME
Three functional blocks of the PRIME and PLC G3 technologies (encoder/decoder, interleaver, and modulator) are studied in detail, for a PLC channel with narrow-band interference (NBI). The study reveals that these three blocks can be used together effectively so as to improve the performance of the overall system in the presence of NBI. We therefore present effective methods for combating NBI in PRIME and PLC G3, based on these three functional blocks
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