Quantum Communication in Spin Systems With Long-Range Interactions

We calculate the fidelity of transmission of a single qubit between distant sites on semi-infinite and finite chains of spins coupled via the magnetic dipole interaction. We show that such systems often perform better than their Heisenberg nearest-neighbour coupled counterparts, and that fidelities closely approaching unity can be attained between the ends of finite chains without any special engineering of the system, although state transfer becomes slow in long chains. We discuss possible optimization methods, and find that, for any length, the best compromise between the quality and the speed of the communication is obtained in a nearly uniform chain of 4 spins.Comment: 15 pages, 8 eps figures, updated references, corrected text and corrected figs. 1, 4 and

ICPR2017 – The Fourth International Conference on Practice Research: overview

This paper reports issues arising from the Fourth International Conference on Practice Research, held in Hong Kong in May 2017. The issues were identified by specially convened group of conference participants, and include the need to develop a better language to describe practice research in terms that make sense to practitioners, improved support for practitioners to conduct research, recognising the different drivers for practice research in different countries, and enhancing practitioners' coordinating and leadership roles

A systematic review of the efficacy of internet-based interventions for depression and anxiety disorders: the possibilities and limitations for feasibility within South Africa

Technological advances may alleviate the burden on South Africa’s mental healthcare system. This study is a systematic review of literature that assesses the efficacy of high quality online interventions for depression and anxiety, and that compares the reviewed studies’ characteristics to the South African context to assist in future developments of online interventions for depression and anxiety within South Africa. This was achieved through using a 2010 systematic review of Griffiths, Farrer, and Christensen as point of departure. This research had two aims: to provide an updated systematic review of the literature reporting on the efficacy of internet-based interventions for depression and anxiety disorders; and to evaluate the possibilities and limitations for the feasibility of implementing internet-based interventions for depression and anxiety disorders in the South African context. Databases accessed were PubMed, PsycINFO, and Cochrane Central Register of Controlled Trials. Included studies must: (i) report on one or more internet-based intervention, (ii) target depression or anxiety or both, (iii) report the effect size or provide enough information to calculate it, (iv) report a measure of symptoms outcome, (v) be a Randomised Controlled Trial, (vi) include a control group that received no active intervention, (vii) be published and peer-reviewed, (viii) have been published after January 2010. The search yielded 2999 potential studies of which 20 full texts were reviewed. Of these, 75% (n=15) of the studies report effect sizes above 0.20, and 25% (n=5) of the studies report effect sizes above 0.80. Themes emergent from literature and included studies distinguished effective from non-effective studies included the use of cognitive behavioural therapy, therapist input and reminders to engage with the intervention, and duration of over 6 weeks. Attrition rates did not differ between experimental and control groups. Sample characteristics between the reviewed interventions and South Africa’s population were found to be different and is discussed. Unfortunately, 37 potential studies could not be accessed and thus not included, although several attempts were made. The majority of studies had effect sizes equal to that of face-to-face therapeutic interventions. Implications of application in South Africa’s context with limited technological familiarity, insufficiency of professionally trained therapists, poor literacy, and high costs of internet data are discussed. It is concluded that with appropriate adaptation, online internet interventions for depression and anxiety would be beneficial to South Africa’s people and assist in lowering the country’s burden of mental health disorders

From Relief to Recovery: Peer Support by Consumers Relieves the Traumas of Disasters and Facilitates Recovery from Mental Illness

This paper is about the expertise those with a lived experience of recovery from personal trauma can bring to disaster relief efforts in the form of peer support

Higher correlations, universal distributions and finite size scaling in the field theory of depinning

Recently we constructed a renormalizable field theory up to two loops for the quasi-static depinning of elastic manifolds in a disordered environment. Here we explore further properties of the theory. We show how higher correlation functions of the displacement field can be computed. Drastic simplifications occur, unveiling much simpler diagrammatic rules than anticipated. This is applied to the universal scaled width-distribution. The expansion in d=4-epsilon predicts that the scaled distribution coincides to the lowest orders with the one for a Gaussian theory with propagator G(q)=1/q^(d+2 \zeta), zeta being the roughness exponent. The deviations from this Gaussian result are small and involve higher correlation functions, which are computed here for different boundary conditions. Other universal quantities are defined and evaluated: We perform a general analysis of the stability of the fixed point. We find that the correction-to-scaling exponent is omega=-epsilon and not -epsilon/3 as used in the analysis of some simulations. A more detailed study of the upper critical dimension is given, where the roughness of interfaces grows as a power of a logarithm instead of a pure power.Comment: 15 pages revtex4. See also preceding article cond-mat/030146

Derivation of the Functional Renormalization Group Beta-Function at order 1/N for Manifolds Pinned by Disorder

In an earlier publication, we have introduced a method to obtain, at large N, the effective action for d-dimensional manifolds in a N-dimensional disordered environment. This allowed to obtain the Functional Renormalization Group (FRG) equation for N=infinity and was shown to reproduce, with no need for ultrametric replica symmetry breaking, the predictions of the Mezard-Parisi solution. Here we compute the corrections at order 1/N. We introduce two novel complementary methods, a diagrammatic and an algebraic one, to perform the complicated resummation of an infinite number of loops, and derive the beta-function of the theory to order 1/N. We present both the effective action and the corresponding functional renormalization group equations. The aim is to explain the conceptual basis and give a detailed account of the novel aspects of such calculations. The analysis of the FRG flow, comparison with other studies, and applications, e.g. to the strong-coupling phase of the Kardar-Parisi-Zhang equation are examined in a subsequent publication.Comment: 62 pages, 97 figure

High-temperature antiferromagnetism in molecular semiconductor thin films and nanostructures

The viability of dilute magnetic semiconductors in applications is linked to the strength of the magnetic couplings, and room temperature operation is still elusive in standard inorganic systems. Molecular semiconductors are emerging as an alternative due to their long spin-relaxation times and ease of processing, but, with the notable exception of vanadium-tetracyanoethylene, magnetic transition temperatures remain well below the boiling point of liquid nitrogen. Here we show that thin films and powders of the molecular semiconductor cobalt phthalocyanine exhibit strong antiferromagnetic coupling, with an exchange energy reaching 100 K. This interaction is up to two orders of magnitude larger than in related phthalocyanines and can be obtained on flexible plastic substrates, under conditions compatible with routine organic electronic device fabrication. Ab initio calculations show that coupling is achieved via superexchange between the singly occupied a(1g) ([Image: see text]) orbitals. By reaching the key milestone of magnetic coupling above 77 K, these results establish quantum spin chains as a potentially useable feature of molecular films