Model for the low-temperature magnetic phases observed in doped YBa_2Cu_3O_{6+x}

A classical statistical model for the antiferromagnetic (AFM) ordering of the Cu-spins in the CuO_2 planes of reduced YBa_2Cu_3O_{6+x} type materials is presented. The magnetic phases considered are the experimentally observed high-temperature AFI phase with ordering vector Q_I=(1/2,1/2,0), and the low-temperature phases: AFII with Q_II=(1/2,1/2,1/2) and intermediate TA (Turn Angle) phases TAI, TAII and TAIII with components of both ordering vectors. It is shown that the AFII and TA phases result from an effective ferromagnetic (FM) type coupling mediated by free spins in the CuO_x basal plane. Good agreement with experimental data is obtained for realistic model parameters.Comment: 11 pages, 2 Postscript figures, Submitted to Phys.Rev.Let

High-speed noise-free optical quantum memory

Quantum networks promise to revolutionise computing, simulation, and communication. Light is the ideal information carrier for quantum networks, as its properties are not degraded by noise in ambient conditions, and it can support large bandwidths enabling fast operations and a large information capacity. Quantum memories, devices that store, manipulate, and release on demand quantum light, have been identified as critical components of photonic quantum networks, because they facilitate scalability. However, any noise introduced by the memory can render the device classical by destroying the quantum character of the light. Here we introduce an intrinsically noise-free memory protocol based on two-photon off-resonant cascaded absorption (ORCA). We consequently demonstrate for the first time successful storage of GHz-bandwidth heralded single photons in a warm atomic vapour with no added noise; confirmed by the unaltered photon statistics upon recall. Our ORCA memory platform meets the stringent noise-requirements for quantum memories whilst offering technical simplicity and high-speed operation, and therefore is immediately applicable to low-latency quantum networks

Theory of noise suppression in {\Lambda}-type quantum memories by means of a cavity

Quantum memories, capable of storing single photons or other quantum states of light, to be retrieved on-demand, offer a route to large-scale quantum information processing with light. A promising class of memories is based on far-off-resonant Raman absorption in ensembles of $\Lambda$-type atoms. However at room temperature these systems exhibit unwanted four-wave mixing, which is prohibitive for applications at the single-photon level. Here we show how this noise can be suppressed by placing the storage medium inside a moderate-finesse optical cavity, thereby removing the main roadblock hindering this approach to quantum memory.Comment: 10 pages, 3 figures. This paper provides the theoretical background to our recent experimental demonstration of noise suppression in a cavity-enhanced Raman-type memory ( arXiv:1510.04625 ). See also the related paper arXiv:1511.05448, which describes numerical modelling of an atom-filled cavity. Comments welcom

Venus-Solar Wind Interaction: Asymmetries and the Escape of O+ Ions

We study the interaction between Venus and the solar wind using a global three-dimensional self-consistent quasi-neutral hybrid (QNH) model. The model treats ions (H+, O+) as particles and electrons as a massless charge neutralising fluid. In the analysed Parker spiral interplanetary magnetic field (IMF) case (IMF = [8.09, 5.88, 0] nT) a notable north-south asymmetry of the magnetic field and plasma exists, especially in the properties of escaping planetary O+ ions. The asymmetry is associated with ion finite gyroradius effects. Furthermore, the IMF x-component results in a dawn-dusk asymmetry. Overall, the QNH model is found to reproduce the main observed plasma and magnetic field regions (the bow shock, the magnetosheath, the magnetic barrier and the magnetotail), implying the potential of the developed model to study the Venusian plasma environment and especially the non-thermal ion escape.Comment: 10 pages, 22 figures, accepted for Planetary and Space Scienc

"Some people are born strange": A Brechtian theater pedagogy as philosophical ethnography

The article explores the role of a Brechtian theater pedagogy as “philosophical ethnography” in four investigative drama based workshops, which took international students’ intercultural “strangeness” experiences as the starting point for aesthetic experimentation. It is argued that a Brechtian theater pedagogy allows for a productive rather than representational orientation in research, which is underpinned by a love for the aesthetic “re-entanglement” of (dis-embodied) language and ethical concerns about mimetic representational acts. To show how a Brechtian research pedagogy functioned as philosophical ethnography, the article maps the aesthetic transformation of participant Jamal’s verbatim account in the drama workshops—from (a) its emergence in a post-creative-writing discussion in Workshop 2, to (b) its enactment as a body sculpture in Workshop 3, and (c) to its translation into a rehearsal piece in Workshop 4.The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The author thanks the School of Education/University of Glasgow (Scotland, United Kingdom) for the PhD scholarship that made this research possibl

Towards an analytical framework of science communication models

This chapter reviews the discussion in science communication circles of models for public communication of science and technology (PCST). It questions the claim that there has been a large-scale shift from a ‘deficit model’ of communication to a ‘dialogue model’, and it demonstrates the survival of the deficit model along with the ambiguities of that model. Similar discussions in related fields of communication, including the critique of dialogue, are briefly sketched. Outlining the complex circumstances governing approaches to PCST, the author argues that communications models often perceived to be opposed can, in fact, coexist when the choices are made explicit. To aid this process, the author proposes an analytical framework of communication models based on deficit, dialogue and participation, including variations on each

Optimal Coherent Filtering for Single Noisy Photons

We introduce a filter using a noise-free quantum buffer with large optical bandwidth that can both filter temporal-spectral modes, as well as inter-convert them and change their frequency. We show that such quantum buffers optimally filter out temporal-spectral noise; producing identical single-photons from many distinguishable noisy single-photon sources with the minimum required reduction in brightness. We then experimentally demonstrate a noise-free quantum buffer in a warm atomic system that is well matched to quantum dots and can outperform all intensity (incoherent) filtering schemes for increasing indistinguishability.Comment: 5 pages, 4 Figure

Analysis of role-play in medical communication training using a theatrical device the fourth wall

BACKGROUND: Communication training is a central part of medical education. The aim of this article is to explore the positions and didactic functions of the fourth wall in medical communication training, using a role-play model basically similar to a theatrical performance. METHOD: The empirical data stem from a communication training model demonstrated at an international workshop for medical teachers and course organizers. The model involves an actress playing a patient, students alternating in the role of the doctor, and a teacher who moderates. The workshop was videotaped and analyzed qualitatively. RESULTS: The analysis of the empirical material revealed three main locations of the fourth wall as it moved and changed qualities during the learning session: 1) A traditional theatre location, where the wall was transparent for the audience, but opaque for the participants in the fiction. 2) A "timeout/reflection" location, where the wall was doubly opaque, for the patient on the one side and the moderator, the doctor and the audience on the other side and 3) an "interviewing the character" location where the wall enclosed everybody in the room. All three locations may contribute to the learning process. CONCLUSION: The theatrical concept 'the fourth wall' may present an additional tool for new understanding of fiction based communication training. Increased understanding of such an activity may help medical teachers/course organizers in planning and evaluating communication training courses

Antiferromagnetic ordering in a 90 K copper oxide superconductor

Using elastic neutron scattering, we evidence a commensurate antiferromagnetic Cu(2) order (AF) in the superconducting (SC) high-$\rm T_c$ cuprate $\rm YBa_2(Cu_{1-y}Co_y)_3O_{7+\delta}$ (y=0.013, $\rm T_c$=93 K). As in the Co-free system, the spin excitation spectrum is dominated by a magnetic resonance peak at 41 meV but with a reduced spectral weight. The substitution of Co thus leads to a state where AF and SC cohabit showing that the CuO$_2$ plane is a highly antiferromagnetically polarizable medium even for a sample where T$_c$ remains optimum.Comment: 3 figure