2,066 research outputs found
On switched Hamiltonian systems
In this paper we study the well-posedness and stability of a class of switched linear passive systems. Instrumental in our approach is the result, also of interest in its own right, that any linear passive input-state-output system with strictly positive storage function can be written as a port-Hamiltonian system
Decoherence and the conditions for the classical control of quantum systems
We find the conditions for one quantum system to function as a classical
controller of another quantum system: the controller must be an open system and
rapidly diagonalised in the basis of the controller variable that is coupled to
the controlled system. This causes decoherence in the controlled system that
can be made small if the rate of diagonalisation is fast. We give a detailed
example based on the quantum optomechanical control of a mechanical resonator.
The resulting equations are similar in structure to recently proposed models
for consistently combining quantum and classical stochastic dynamics
Switched networks and complementarity
A modeling framework is proposed for circuits that are subject both to externally induced switches (time events) and to state events. The framework applies to switched networks with linear and piecewise-linear elements, including diodes. We show that the linear complementarity formulation, which already has proved effective for piecewise-linear networks, can be extended in a natural way to also cover switching circuits. To achieve this, we use a generalization of the linear complementarity problem known as the cone-complementarity problem. We show that the proposed framework is sound in the sense that existence and uniqueness of solutions is guaranteed under a passivity assumption. We prove that only first-order impulses occur and characterize all situations that give rise to a state jump; moreover, we provide rules that determine the jump. Finally, we show that within our framework, energy cannot increase as a result of a jump, and we derive a stability result from this
Optimal generation of entanglement under local control
We study the optimal generation of entanglement between two qubits subject to
local unitary control. With the only assumptions of linear control and unitary
dynamics, by means of a numerical protocol based on the variational approach
(Pontryagin's Minimum Principle), we evaluate the optimal control strategy
leading to the maximal achievable entanglement in an arbitrary interaction
time, taking into account the energy cost associated to the controls. In our
model we can arbitrarily choose the relative weight between a large
entanglement and a small energy cost.Comment: 4 page
Photoionization of helium by attosecond pulses: extraction of spectra from correlated wave functions
We investigate the photoionization spectrum of helium by attosecond XUV
pulses both in the spectral region of doubly excited resonances as well as
above the double ionization threshold. In order to probe for convergence, we
compare three techniques to extract photoelectron spectra from the wavepacket
resulting from the integration of the time-dependent Schroedinger equation in
a finite-element discrete variable representation basis. These techniques are:
projection on products of hydrogenic bound and continuum states, projection
onto multi-channel scattering states computed in a B-spline close-coupling
basis, and a technique based on exterior complex scaling (ECS) implemented in
the same basis used for the time propagation. These methods allow to monitor
the population of continuum states in wavepackets created with ultrashort
pulses in different regimes. Applications include photo cross sections and
anisotropy parameters in the spectral region of doubly excited resonances,
time-resolved photoexcitation of autoionizing resonances in an attosecond
pump-probe setting, and the energy and angular distribution of correlated
wavepackets for two-photon double ionization.Comment: 19 pages, 12 figure
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