Choice of Measurement Sets in Qubit Tomography

Optimal generalized measurements for state estimation are well understood. However, practical quantum state tomography is typically performed using a fixed set of projective measurements and the question of how to choose these measurements has been largely unexplored in the literature. In this work we develop theoretical asymptotic bounds for the average fidelity of pure qubit tomography using measurement sets whose axes correspond to vertices of Platonic solids. We also present complete simulations of maximum likelihood tomography for mixed qubit states using the Platonic solid measurements. We show that overcomplete measurement sets can be used to improve the accuracy of tomographic reconstructions.Comment: 13 Pages, 6 figure

Chemical functionalization of emulsion-templated porous polymers by thiol–ene “click” chemistry

Highly porous polymers (polyHIPEs) have been prepared by the photopolymerization of high internal phase emulsions (HIPEs) with varying ratios of thiol and acrylate monomers. The resulting polymers have a nominal porosity of 80%, and are seen to have a well-defined, interconnected pore morphology, with average pore diameters ranging from 30 to 60 μm. The polyHIPE polymers have been shown using a colourimetric (Ellman's) assay to contain residual thiols which are reactive towards a range of (meth)acrylates (hexafluoroisopropyl acrylate, fluorescein O-acrylate and poly(ethylene glycol) methyl ether methacrylate). Functionalization was explored using thermally- and UV-initiated radical-mediated “click” reactions and an amine-catalysed Michael addition reaction. The extent of functionalization was investigated qualitatively and quantitatively using a range of techniques (solid state NMR spectroscopy; FTIR spectroscopy; X-ray photoelectron spectroscopy (XPS); observation of fluorescence); high levels of conversion (up to 90–95%) were observed for the thermally-initiated radical reaction and the Michael reaction

Building Digital Identities: The Challenges, Risks and Opportunities of Collecting Behavioural Attributes for new Digital Identity Systems.

The provision of legal identity for all is increasingly viewed as a key mechanism for driving development goals. Behavioural attributes produced through digital interactions may have significant potential for enabling access to a legal identity for all, however the social, legal, and technical affordances and implications remain under-explored.University of Exeter and CoelitionEconomic and Social Research Council (ESRC

Quantum process tomography of a controlled-NOT gate

We demonstrate complete characterization of a two-qubit entangling process - a linear optics controlled-NOT gate operating with coincident detection - by quantum process tomography. We use maximum-likelihood estimation to convert the experimental data into a physical process matrix. The process matrix allows accurate prediction of the operation of the gate for arbitrary input states, and calculation of gate performance measures such as the average gate fidelity, average purity and entangling capability of our gate, which are 0.90, 0.83 and 0.73, respectively.Comment: 4 pages, 2 figures. v2 contains new data corresponding to improved gate operation. Figure quality slightly reduced for arXi

From antiferromagnetism to superconductivity in Fe 1+y(Te1-x,Sex) (0 < x < 0.20): a neutron powder diffraction analysis

The nuclear and magnetic structure of Fe1+y(Te1-x,Sex) (0 < x < 0.20) compounds was analyzed between 2 K and 300 K by means of Rietveld refinement of neutron powder diffraction data. Samples with x < 0.075 undergo a tetragonal to monoclinic phase transition at low temperature, whose critical temperature decreases with increasing Se content; this structural transition is strictly coupled to a long range antiferromagnetic ordering at the Fe site. Both the transition to a monoclinic phase and the long range antiferromagnetism are suppressed for 0.10 < x < 0.20. The onset of the structural and of the magnetic transition remains coincident with the increase of Se substitution. The low temperature monoclinic crystal structure has been revised. Superconductivity arises for x > 0.05, therefore a significant region where superconductivity and long range antiferromagnetism coexist is present in the pseudo-binary FeTe - FeSe phase diagram.Comment: 33 pages, 4 tables, 13 figure

“everything in one place”

Purpose: To describe older adults’ perspectives on a new patient education manual for the recovery process after hip fracture. Materials and methods: The Fracture Recovery for Seniors at Home (FReSH) Start manual is an evidence- based manual for older adults with fall-related hip fracture. The manual aims to support the transition from hospital to home by facilitating self- management of the recovery process. We enrolled 31 community-dwelling older adults with previous fall-related hip fracture and one family member. We collected data using a telephone-based questionnaire with eight five-point Likert items and four semi-structured open-ended questions to explore participants’ perceptions on the structure, content, and illustration of the manual. The questionnaire also asked participants to rate the overall utility (out of 10 points) and length of the manual. We used content analysis to describe main themes from responses to the open-ended interview questions. Results: Participants’ ratings for structure, content, and illustrations ranged from 4 to 5 (agree to highly agree), and the median usefulness rating was 9 (10th percentile: 7, 90th percentile: 10). Main themes from the content analysis included: ease of use and presentation; health literacy; illustration utility; health care team delivery; general impression, information support from hospital to home; emotional and decision-making support; and the novelty of the manual. Conclusion: The FReSH Start manual was perceived as comprehensive in content and acceptable for use with older adults post-fall- related hip fracture. Participants expressed a need for delivery and explanation of the manual by a health care team member

Structure and giant magnetoresistance of granular Co-Cu nanolayers prepared by cross-beam PLD

A series of Co_xCu_{100-x} (x = 0, 40...75, 100) layers with thicknesses in-between 13 nm and 55 nm were prepared on silicon substrates using cross-beam pulsed laser deposition. Wide-angle X-ray diffraction (WAXRD), transmission electron microscopy (TEM) and electrical transport measurements revealed a structure consisting of decomposed cobalt and copper grains with grain sizes of about 10 nm. The influence of cobalt content and layer thickness on the grain size is discussed. Electron diffraction (ED) indicates the presence of an intermetallic Co-Cu phase of Cu3Au structure-type. Thermal treatment at temperatures between 525 K and 750 K results in the progressive decomposition of Co and Cu, with an increase of the grain sizes up to about 100 nm. This is tunable by controlling the temperature and duration of the anneal, and is directly observable in WAXRD patterns and TEM images. A careful analysis of grain size and the coherence length of the radiation used allows for an accurate interpretation of the X-ray diffraction patterns, by taking into account coherent and non-coherent scattering. The alloy films show a giant magnetoresistance of 1...2.3 % with the maximum obtained after annealing at around 725 K.Comment: 9 pages, 9 figure