104,352 research outputs found
Quantifying the decay of quantum properties in single-mode states
The dissipative dynamics of Gaussian squeezed states (GSS) and coherent
superposition states (CSS) are analytically obtained and compared. Time scales
for sustaining different quantum properties such as squeezing, negativity of
the Wigner function or photon number distribution are calculated. Some of these
characteristic times also depend on initial conditions. For example, in the
particular case of squeezing, we find that while the squeezing of CSS is only
visible for small enough values of the field intensity, in GSS it is
independent of this quantity, which may be experimentally advantageous. The
asymptotic dynamics however is quite similar as revealed by the time evolution
of the fidelity between states of the two classes.Comment: Accepted versio
A particle system in interaction with a rapidly varying environment: Mean field limits and applications
We study an interacting particle system whose dynamics depends on an
interacting random environment. As the number of particles grows large, the
transition rate of the particles slows down (perhaps because they share a
common resource of fixed capacity). The transition rate of a particle is
determined by its state, by the empirical distribution of all the particles and
by a rapidly varying environment. The transitions of the environment are
determined by the empirical distribution of the particles. We prove the
propagation of chaos on the path space of the particles and establish that the
limiting trajectory of the empirical measure of the states of the particles
satisfies a deterministic differential equation. This deterministic
differential equation involves the time averages of the environment process.
We apply our results to analyze the performance of communication networks
where users access some resources using random distributed multi-access
algorithms. For these networks, we show that the environment process
corresponds to a process describing the number of clients in a certain loss
network, which allows us provide simple and explicit expressions of the network
performance.Comment: 31 pages, 2 figure
The speed of quantum information and the preferred frame: analysis of experimental data
The results of EPR experiments performed in Geneva are analyzed in the frame
of the cosmic microwave background radiation, generally considered as a good
candidate for playing the role of preferred frame. We set a lower bound for the
speed of quantum information in this frame at 1.5 x 10^4 c.Comment: 9 pages including 3 figure
On Modeling Heterogeneous Wireless Networks Using Non-Poisson Point Processes
Future wireless networks are required to support 1000 times higher data rate,
than the current LTE standard. In order to meet the ever increasing demand, it
is inevitable that, future wireless networks will have to develop seamless
interconnection between multiple technologies. A manifestation of this idea is
the collaboration among different types of network tiers such as macro and
small cells, leading to the so-called heterogeneous networks (HetNets).
Researchers have used stochastic geometry to analyze such networks and
understand their real potential. Unsurprisingly, it has been revealed that
interference has a detrimental effect on performance, especially if not modeled
properly. Interference can be correlated in space and/or time, which has been
overlooked in the past. For instance, it is normally assumed that the nodes are
located completely independent of each other and follow a homogeneous Poisson
point process (PPP), which is not necessarily true in real networks since the
node locations are spatially dependent. In addition, the interference
correlation created by correlated stochastic processes has mostly been ignored.
To this end, we take a different approach in modeling the interference where we
use non-PPP, as well as we study the impact of spatial and temporal correlation
on the performance of HetNets. To illustrate the impact of correlation on
performance, we consider three case studies from real-life scenarios.
Specifically, we use massive multiple-input multiple-output (MIMO) to
understand the impact of spatial correlation; we use the random medium access
protocol to examine the temporal correlation; and we use cooperative relay
networks to illustrate the spatial-temporal correlation. We present several
numerical examples through which we demonstrate the impact of various
correlation types on the performance of HetNets.Comment: Submitted to IEEE Communications Magazin
Static Analysis of Run-Time Errors in Embedded Real-Time Parallel C Programs
We present a static analysis by Abstract Interpretation to check for run-time
errors in parallel and multi-threaded C programs. Following our work on
Astr\'ee, we focus on embedded critical programs without recursion nor dynamic
memory allocation, but extend the analysis to a static set of threads
communicating implicitly through a shared memory and explicitly using a finite
set of mutual exclusion locks, and scheduled according to a real-time
scheduling policy and fixed priorities. Our method is thread-modular. It is
based on a slightly modified non-parallel analysis that, when analyzing a
thread, applies and enriches an abstract set of thread interferences. An
iterator then re-analyzes each thread in turn until interferences stabilize. We
prove the soundness of our method with respect to the sequential consistency
semantics, but also with respect to a reasonable weakly consistent memory
semantics. We also show how to take into account mutual exclusion and thread
priorities through a partitioning over an abstraction of the scheduler state.
We present preliminary experimental results analyzing an industrial program
with our prototype, Th\'es\'ee, and demonstrate the scalability of our
approach
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