Dynamics of multiply charged ions in intense laser fields

We numerically investigate the dynamics of multiply charged hydrogenic ions in near-optical linearly polarized laser fields with intensities of order 10^16 to 10^17 W/cm^2. Depending on the charge state Z of the ion the relation of strength between laser field and ionic core changes. We find around Z=12 typical multiphoton dynamics and for Z=3 tunneling behaviour, however with clear relativistic signatures. In first order in v/c the magnetic field component of the laser field induces a Z-dependent drift in the laser propagation direction and a substantial Z-dependent angular momentum with repect to the ionic core. While spin oscillations occur already in first order in v/c as described by the Pauli equation, spin induced forces via spin orbit coupling only appear in the parameter regime where (v/c)^2 corrections are significant. In this regime for Z=12 ions we show strong splittings of resonant spectral lines due to spin-orbit coupling and substantial corrections to the conventional Stark shift due to the relativistic mass shift while those to the Darwin term are shown to be small. For smaller charges or higher laser intensities, parts of the electronic wavepacket may tunnel through the potential barrier of the ionic core, and when recombining are shown to give rise to keV harmonics in the radiation spectrum. Some parts of the wavepacket do not recombine after ionisation and we find very energetic electrons in the weakly relativistic regime of above threshold ionization.Comment: submitte

Charge fluctuation induced dephasing of exchange coupled spin qubits

Exchange coupled {\it spin} qubits in semiconductor nanostructures are shown to be vulnerable to dephasing caused by {\it charge noise} invariably present in the semiconductor environment. This decoherence of exchange gate by environmental charge fluctuations arises from the fundamental Coulombic nature of the Heisenberg coupling, and presents a serious challenge to the scalability of the widely studied exchange gate solid state spin quantum computer architectures. We estimate dephasing times for coupled spin qubits in a wide range (from 1 ns up to $> 1 \mu$s) depending on the exchange coupling strength and its sensitivity to charge fluctuations.Comment: 4 pages, 3 figure

Semantic modelling of learning objects and instruction

We introduce an ontology-based semantic modelling framework that addresses subject domain modelling, instruction modelling, and interoperability aspects in the development of complex reusable learning objects. Ontologies are knowledge representation frameworks, ideally suited to support knowledge-based modelling of these learning objects. We illustrate the benefits of semantic modelling for learning object assemblies within the context of standards such as SCORM Sequencing and Navigation and Learning Object Metadata

Thermalization and Lyapunov Exponents in the Yang-Mills-Higgs Theory

We investigate thermalization processes occurring at different time scales in the Yang-Mills-Higgs system at high temperatures. We determine the largest Lyapunov exponent associated with the gauge fields and verify its relation to the perturbatively calculated damping rate of a static gauge boson.Comment: 33 pages (revtex), 4 PS figures, submitted to PR