17,384 research outputs found
On the infeasibility of entanglement generation in Gaussian quantum systems via classical control
This paper uses a system theoretic approach to show that classical linear
time invariant controllers cannot generate steady state entanglement in a
bipartite Gaussian quantum system which is initialized in a Gaussian state. The
paper also shows that the use of classical linear controllers cannot generate
entanglement in a finite time from a bipartite system initialized in a
separable Gaussian state. The approach reveals connections between system
theoretic concepts and the well known physical principle that local operations
and classical communications cannot generate entangled states starting from
separable states.Comment: 6 pages, 3 figures. To appear in IEEE Transactions on Automatic
Control, 201
Association between Antibiotic Prescribing in Pregnancy and Cerebral Palsy or Epilepsy in Children Born at Term: A Cohort Study Using The Health Improvement Network.
Between 19%-44% pregnant women are prescribed antibiotics during pregnancy. A single, large randomised-controlled-trial (ORACLE Childhood Study II) found an increased risk of childhood cerebral palsy and possibly epilepsy following prophylactic antibiotic use in pregnant women with spontaneous preterm labour. We ascertained whether this outcome could be reproduced across the population of babies delivered at term and prospectively followed in primary-care using data from The Health Improvement Network
Robust observer for uncertain linear quantum systems
In the theory of quantum dynamical filtering, one of the biggest issues is
that the underlying system dynamics represented by a quantum stochastic
differential equation must be known exactly in order that the corresponding
filter provides an optimal performance; however, this assumption is generally
unrealistic. Therefore, in this paper, we consider a class of linear quantum
systems subjected to time-varying norm-bounded parametric uncertainties and
then propose a robust observer such that the variance of the estimation error
is guaranteed to be within a certain bound. Although in the linear case much of
classical control theory can be applied to quantum systems, the quantum robust
observer obtained in this paper does not have a classical analogue due to the
system's specific structure with respect to the uncertainties. Moreover, by
considering a typical quantum control problem, we show that the proposed robust
observer is fairly robust against a parametric uncertainty of the system even
when the other estimators--the optimal Kalman filter and risk-sensitive
observer--fail in the estimation.Comment: 11 pages, 1 figur
Generalizing Negative Imaginary Systems Theory to Include Free Body Dynamics: Control of Highly Resonant Structures with Free Body Motion
Negative imaginary (NI) systems play an important role in the robust control
of highly resonant flexible structures. In this paper, a generalized NI system
framework is presented. A new NI system definition is given, which allows for
flexible structure systems with colocated force actuators and position sensors,
and with free body motion. This definition extends the existing definitions of
NI systems. Also, necessary and sufficient conditions are provided for the
stability of positive feedback control systems where the plant is NI according
to the new definition and the controller is strictly negative imaginary. The
stability conditions in this paper are given purely in terms of properties of
the plant and controller transfer function matrices, although the proofs rely
on state space techniques. Furthermore, the stability conditions given are
independent of the plant and controller system order. As an application of
these results, a case study involving the control of a flexible robotic arm
with a piezo-electric actuator and sensor is presented
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