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

The blurring boundaries between synchronicity and asynchronicity:new communicative situations in work-related Instant Messaging

Instant messaging is one of the most popular communication technologies in virtual teams, enabling interactions to intertwine whole working days, thus creating the sense of copresence for team members who are geographically dispersed. Through close linguistic analyses of naturally occurring data from a virtual team, this article discusses the implications of two novel communicative situations enabled by instant messaging: presence information and the persistence of transcript. The preliminary findings of this study indicate that these new communicative situations require the flouting or rethinking of previously existing interactional norms and that communicative practices employed by the team members are not yet conventionalized/normalized, the expectations and interpretations of interactional rituals and timing vary highly, even within the same virtual team

Non-collinear coupling between magnetic adatoms in carbon nanotubes

The long range character of the exchange coupling between localized magnetic moments indirectly mediated by the conduction electrons of metallic hosts often plays a significant role in determining the magnetic order of low-dimensional structures. In addition to this indirect coupling, here we show that the direct exchange interaction that arises when the moments are not too far apart may induce a non-collinear magnetic order that cannot be characterized by a Heisenberg-like interaction between the magnetic moments. We argue that this effect can be manipulated to control the magnetization alignment of magnetic dimers adsorbed to the walls of carbon nanotubes.Comment: 13 pages, 5 figures, submitted to PR

On the Geometry of Surface Stress

We present a fully general derivation of the Laplace--Young formula and discuss the interplay between the intrinsic surface geometry and the extrinsic one ensuing from the immersion of the surface in the ordinary euclidean three-dimensional space. We prove that the (reversible) work done in a general surface deformation can be expressed in terms of the surface stress tensor and the variation of the intrinsic surface metric

Out-of-plane nesting driven spin spiral in ultrathin Fe/Cu(001) films

Epitaxial ultrathin Fe films on fcc Cu(001) exhibit a spin spiral (SS), in contrast to the ferromagnetism of bulk bcc Fe. We study the in-plane and out-of-plane Fermi surfaces (FSs) of the SS in 8 monolayer Fe/Cu(001) films using energy dependent soft x-ray momentum-resolved photoemission spectroscopy. We show that the SS originates in nested regions confined to out-of-plane FSs, which are drastically modified compared to in-plane FSs. From precise reciprocal space maps in successive zones, we obtain the associated real space compressive strain of 1.5+-0.5% along c-axis. An autocorrelation analysis quantifies the incommensurate ordering vector q=(2pi/a)(0,0,~0.86), favoring a SS and consistent with magneto-optic Kerr effect experiments. The results reveal the importance of in-plane and out-of-plane FS mapping for ultrathin films.Comment: 4 pages, 3 figure

Magnetoelastic coupling in iron

Exchange interactions in {\alpha}- and {\gamma}-Fe are investigated within an ab-initio spin spiral approach. We have performed total energy calculations for different magnetic structures as a function of lattice distortions, related with various cell volumes and the Bain tetragonal deformations. The effective exchange parameters in {\gamma}-Fe are very sensitive to the lattice distortions, leading to the ferromagnetic ground state for the tetragonal deformation or increase of the volume cell. At the same time, the magnetic-structure-independent part of the total energy changes very slowly with the tetragonal deformations. The computational results demonstrate a strong mutual dependence of crystal and magnetic structures in Fe and explain the observable "anti-Invar" behavior of thermal expansion coefficient in {\gamma}-Fe.Comment: Submitted to Phys. Rev.

Perceptions on the role of evidence: an English alcohol policy case study

This paper explores the competing influences which inform public health policy and describes the role that research evidence plays within the policy-making process. In particular it draws on a recent English alcohol policy case study to assess the role of evidence in informing policy and practice. Semi-structured interviews with key national, regional and local policy informants were transcribed and analysed thematically. A strong theme identified was that of the role of evidence. Findings are discussed in the context of competing views on what constitutes appropriate evidence for policy-making

Soft methods, hard targets: regional alcohol managers as a policy network

Regional Alcohol Managers (RAMs) was employed in the nine English health regions over 2008–2011. Their mission was to impact on the ‘hard target’ of Alcohol-Related Hospital Admissions (AHRAs) through the ‘soft methods’ of persuasion and influence: working with local partners on evidence-based interventions. Drawing on a qualitative evaluation, this article shows how a central government policy imperative (ARHAs) led to ‘government at a distance’ responses, including the introduction of RAMs. The processes involved in shaping and delivering this function bore the hallmarks of a complex, interactive policy network model, involving individuals whose bearings and roles were flexible and sometimes ambiguous. While there were overlaps and blurring of boundaries, there were three levels of policy network: central government, regional and local. As the ‘network in the middle’, the RAMs were pulled in both directions by conflicting agendas but were also able to have an impact on central and local policy

The alcohol improvement programme: evaluation of an initiative to address alcohol-related health harm in England

Aims: The evaluation aimed to assess the impact of The Alcohol Improvement Programme (AIP). This was a UK Department of Health initiative (April 2008–March 2011) aiming to contribute to the reduction of alcohol-related harm as measured by a reduction in the rate of increase in alcohol-related hospital admissions (ARHAs). Methods: The evaluation (March 2010–September 2011) used a mix of qualitative and quantitative methods to assess the impact of the AIP on ARHAs, to describe and assess the process of implementation, and to identify elements of the programme which might serve as a ‘legacy’ for the future. Results: There was no evidence that the AIP had an impact on reducing the rise in the rate of ARHAs. The AIP was successfully delivered, increased the priority given to alcohol-related harm on local policy agendas and strengthened the infrastructure for the delivery of interventions. Conclusion: Although there was no measurable short-term impact on the rise in the rate of ARHAs, the AIP helped to set up a strategic response and a delivery infrastructure as a first, necessary step in working towards that goal. There are a number of valuable elements in the AIP which should be retained and repackaged to fit into new policy contexts