67 research outputs found
Flux qubit on mesoscopic nonsuperconducting ring
The possibility of making a flux qubit on nonsuperconducting mesoscopic
ballistic quasi 1D ring is discussed. We showed that such ring can be
effectively reduced to a two-state system with two external control parameters.
The two states carry opposite persistent currents and are coupled by tunneling
which leads to a quantum superposition of states. The qubit states can be
manipulated by resonant microwave pulses. The flux state of the sample can be
measured by a SQUID magnetometer. Two or more qubits can be coupled by the flux
the circulating currents generate. The problem of decoherence is also
discussed.Comment: Phys. Rev. B. (accepted
Entanglement of distant flux qubits mediated by non-classical electromagnetic field
The mechanism for entanglement of two flux qubits each interacting with a
single mode electromagnetic field is discussed. By performing a Bell state
measurements (BSM) on photons we find the two qubits in an entangled state
depending on the system parameters. We discuss the results for two initial
states and take into consideration the influence of decoherence.Comment: 20 pages, 8 figure
Entanglement of qubits via a nonlinear resonator
Coherent coupling of two qubits mediated by a nonlinear resonator is studied.
It is shown that the amount of entanglement accessible in the evolution depends
both on the strength of nonlinearity in the Hamiltonian of the resonator and on
the initial preparation of the system. The created entanglement survives in the
presence of decoherence.Comment: 6 pages, 10 figure
Gate-tunable black phosphorus spin valve with nanosecond spin lifetimes
Two-dimensional materials offer new opportunities for both fundamental
science and technological applications, by exploiting the electron spin. While
graphene is very promising for spin communication due to its extraordinary
electron mobility, the lack of a band gap restricts its prospects for
semiconducting spin devices such as spin diodes and bipolar spin transistors.
The recent emergence of 2D semiconductors could help overcome this basic
challenge. In this letter we report the first important step towards making 2D
semiconductor spin devices. We have fabricated a spin valve based on ultra-thin
(5 nm) semiconducting black phosphorus (bP), and established fundamental spin
properties of this spin channel material which supports all electrical spin
injection, transport, precession and detection up to room temperature (RT).
Inserting a few layers of boron nitride between the ferromagnetic electrodes
and bP alleviates the notorious conductivity mismatch problem and allows
efficient electrical spin injection into an n-type bP. In the non-local spin
valve geometry we measure Hanle spin precession and observe spin relaxation
times as high as 4 ns, with spin relaxation lengths exceeding 6 um. Our
experimental results are in a very good agreement with first-principles
calculations and demonstrate that Elliott-Yafet spin relaxation mechanism is
dominant. We also demonstrate that spin transport in ultra-thin bP depends
strongly on the charge carrier concentration, and can be manipulated by the
electric field effect
The XMM-Newton serendipitous survey: VIII. the first XMM-Newton serendipitous source catalogue from overlapping observations
Context. XMM-Newton has observed the X-ray sky since early 2000. The XMM-Newton Survey Science Centre Consortium has published catalogues of X-ray and ultraviolet sources found serendipitously in the individual observations. This series is now augmented by a catalogue dedicated to X-ray sources detected in spatially overlapping XMM-Newton observations. Aims. The aim of this catalogue is to explore repeatedly observed sky regions. It thus makes use of the long(er) effective exposure time per sky area and offers the opportunity to investigate long-term flux variability directly through the source-detection process. Methods. A new standardised strategy for simultaneous source detection on multiple observations was introduced, including an adaptive-smoothing method to describe the image background. It was coded as a new task within the XMM-Newton Science Analysis System and used to compile a catalogue of sources from 434 stacks comprising 1789 overlapping XMM-Newton observations that entered the 3XMM-DR7 catalogue, have a low background and full-frame readout of all EPIC cameras. Results. The first stacked catalogue is called 3XMM-DR7s. It contains 71 951 unique sources with positions and parameters such as fluxes, hardness ratios, quality estimates, and information on inter-observation variability, directly derived from a simultaneous fit. Source parameters are calculated for the stack and for each contributing observation. About 15% of the sources are new with respect to 3XMM-DR7. Through stacked source detection, the parameters of repeatedly observed sources are determined with higher accuracy than in the individual observations. The method is more sensitive to faint sources and tends to produce fewer spurious detections. Conclusions. With this first stacked catalogue we demonstrate the feasibility and benefit of the approach. It supplements the large data base of XMM-Newton detections with additional, in particular faint, sources and adds variability information. In the future, the catalogue will be expanded to larger samples and continued within the series of serendipitous XMM-Newton source catalogues.FJC acknowledges financial support through grant AYA2015-64346-C2-1P (MINECO/FEDER) and MTC through grant ESP2016-76683-C3-1R (MINECO/FEDER
Cataclysmic Variables from Sloan Digital Sky Survey V -- the search for period bouncers continues
SDSS-V is carrying out a dedicated survey for white dwarfs, single and in
binaries, and we report the analysis of the spectroscopy of cataclysmic
variables (CVs) and CV candidates obtained during the final plug plate
observations of SDSS. We identify eight new CVs, spectroscopically confirm 53
and refute eleven published CV candidates, and we report 21 new or improved
orbital periods. Combined with previously published data, the orbital period
distribution of the SDSS-V CVs does not clearly exhibit a period gap. This is
consistent with previous findings that spectroscopically identified CVs have a
larger proportion of short-period systems compared to samples identified from
photometric variability. Remarkably, despite a systematic search, we find very
few period bouncers. We estimate the space density of period bouncers to be
, i.e. they represent only a few per
cent of the total CV population. This suggests that during their final phase of
evolution, CVs either destroy the donor, e.g. via a merger, or that they become
detached and cease mass transfer.Comment: Submitted to MNRA
Intermediate care in caring for dementia, the point of view of general practitioners: A key informant survey across Europe.
Background: Intermediate care is often defined as healthcare occurring somewhere between traditional primary (community) and secondary (hospital) care settings. High quality intermediate care is important in dementia, may prevent caregiver burnout and also lead to optimal care for people with dementia. However, very little is known about the point of intermediate care for persons with dementia in Europe. Research questions: What intermediate care services exist and how are they utilized in the care of people with dementia in Europe? Objective: This study aims at describing the point of view of General Practitioners on intermediate care services for people with dementia across Europe. Methods: Key informant survey was sent to GPs via a self-developed questionnaire with space for open ended comments. 16 European countries participated to this cross-sectional mixed method study. Given the volunteer nature of the study, no minimum sample size requirements were applied to participation. Convenience sampling technique was used to address variations due to regional variations and regulations within the same country. Descriptive analyses of all intermediate care facilities groups by countries were performed. Qualitative analyses approach was used for the optional-free text to exemplify and/or complete the reasons contained in the closed response categories. Results: The questionnaire was sent to 16 European countries. 583 questionnaires were analyzed. The responding physicians were 48 (± 11) years old on average and they had been in practice for an average of 18 (+ /11) years. The types of intermediate care considered were integrated at-home services, respite and relief services, day care centers and nursing homes. Their availability was considered very inhomogeneous by the majority of respondents. The main benefits of intermediate care cited were better medical care for the patient (78%), better quality of life for the caregiver (67%), prevention of the caregiver burden (73%) and a break for the caregiver (59%). The reported difficulties were: accessing these facilities due to limited financial support (76%) and cumbersome administrative procedures (67%). Many other facets of our findings were captured in the qualitative themes that emerged. Conclusion: Intermediate care in Europe is diverse and heterogeneous. Major concerns of GPs are about the cost issues and the cumbersome administrative procedures to access them
Stakeholders' views and experiences of care and interventions for addressing frailty and pre-frailty:a meta-synthesis of qualitative evidence
Frailty is a common condition in older age and is a public health concern which requires integrated care and involves different stakeholders. This meta-synthesis focuses on experiences, understanding, and attitudes towards screening, care, intervention and prevention for frailty across frail and healthy older persons, caregivers, health and social care practitioners. Studies published since 2001 were identified through search of electronic databases; 81 eligible papers were identified and read in full, and 45 papers were finally included and synthesized. The synthesis was conducted with a meta-ethnographic approach. We identified four key themes: Uncertainty about malleability of frailty; Strategies to prevent or to respond to frailty; Capacity to care and person and family-centred service provision; Power and choice. A bottom-up approach which emphasises and works in synchrony with frail older people's and their families' values, goals, resources and optimisation strategies is necessary. A greater employment of psychological skills, enhancing communication abilities and tools to overcome disempowering attitudes should inform care organisation, resulting in more efficient and satisfactory use of services. Public health communication about prevention and management of frailty should be founded on a paradigm of resilience, balanced acceptance, and coping. Addressing stakeholders' views about the preventability of frailty was seen as a salient need
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