Entanglement properties of multipartite entangled states under the influence of decoherence

We investigate entanglement properties of multipartite states under the influence of decoherence. We show that the lifetime of (distillable) entanglement for GHZ-type superposition states decreases with the size of the system, while for a class of other states -namely all graph states with constant degree- the lifetime is independent of the system size. We show that these results are largely independent of the specific decoherence model and are in particular valid for all models which deal with individual couplings of particles to independent environments, described by some quantum optical master equation of Lindblad form. For GHZ states, we derive analytic expressions for the lifetime of distillable entanglement and determine when the state becomes fully separable. For all graph states, we derive lower and upper bounds on the lifetime of entanglement. To this aim, we establish a method to calculate the spectrum of the partial transposition for all mixed states which are diagonal in a graph state basis. We also consider entanglement between different groups of particles and determine the corresponding lifetimes as well as the change of the kind of entanglement with time. This enables us to investigate the behavior of entanglement under re-scaling and in the limit of large (infinite) number of particles. Finally we investigate the lifetime of encoded quantum superposition states and show that one can define an effective time in the encoded system which can be orders of magnitude smaller than the physical time. This provides an alternative view on quantum error correction and examples of states whose lifetime of entanglement (between groups of particles) in fact increases with the size of the system.Comment: 27 pages, 11 figure

Medical Research Involving Children - Giving Weight to Children's Views

The quality of health care for children depends much on the availability of relevant results from medical research with children as subjects. Yet, because of their vulnerability and assumed incompetence to take part in decision-making, children have often been excluded from taking part in medical research, so as to prevent them from harm. Empirical data on children's competence to consent to such research used to be rare, but recent developments in this field have created more insights in the myths and realities concerning minor patients' capacities to decide on medical research participation. Against the background of relevant international, European and domestic legal frameworks concerning the rights of children as participants in medical research, this article goes into instruments such as MacCAT-CR, a semi-structured interview format useable as a competence assessment tool for clinical research involving children. On the basis of this, several recommendations are defined to enhance such research, as these may do sufficient justice to the health interests and the capacities of children, while at the same time supporting researchers and child research participants when facing decisions about pediatric research options

Completeness of the classical 2D Ising model and universal quantum computation

We prove that the 2D Ising model is complete in the sense that the partition function of any classical q-state spin model (on an arbitrary graph) can be expressed as a special instance of the partition function of a 2D Ising model with complex inhomogeneous couplings and external fields. In the case where the original model is an Ising or Potts-type model, we find that the corresponding 2D square lattice requires only polynomially more spins w.r.t the original one, and we give a constructive method to map such models to the 2D Ising model. For more general models the overhead in system size may be exponential. The results are established by connecting classical spin models with measurement-based quantum computation and invoking the universality of the 2D cluster states.Comment: 4 pages, 1 figure. Minor change

Modelling of Plastic Anisotropy and Plastic Volume Change

An anisotropic material law for metallic materials is presented which is able to describe plastic volume changes in the elastic-plastic transition area. The modelling includes a mixed isotropic-kinematic hardening rule. The strategy of evolution is used to fit the material law to yield loci of X5CrNi18.10. The additional extension of the model by anisotropic hardening permits the description of the deformation anisotropy. Finally, the plane compression of a thick cylinder is used to show the effect of the material law used. Therefore the outer radius is equally reduced and the deformation behaviour of the inner radius is observed

Robust single-parameter quantized charge pumping

This paper investigates a scheme for quantized charge pumping based on single-parameter modulation. The device was realized in an AlGaAs-GaAs gated nanowire. We find a remarkable robustness of the quantized regime against variations in the driving signal, which increases with applied rf power. This feature together with its simple configuration makes this device a potential module for a scalable source of quantized current.Comment: Submitted to Appl. Phys. Let

Targeting of IL-2 to cytotoxic lymphocytes as an improved method of cytokine-driven immunotherapy

The use of high-dose interleukin-2 (IL-2) has fallen out of favor due to severe life-threatening side effects. We have recently described a unique way of directly targeting IL-2 to cytotoxic lymphocytes using a virally encoded immune evasion protein and an IL-2 mutant that avoids off-target side effects such as activation of regulatory T cells and vascular endothelium