77 research outputs found
Scalable Focused Ion Beam Creation of Nearly Lifetime-Limited Single Quantum Emitters in Diamond Nanostructures
The controlled creation of defect center---nanocavity systems is one of the
outstanding challenges for efficiently interfacing spin quantum memories with
photons for photon-based entanglement operations in a quantum network. Here, we
demonstrate direct, maskless creation of atom-like single silicon-vacancy (SiV)
centers in diamond nanostructures via focused ion beam implantation with nm lateral precision and nm positioning accuracy relative to a
nanocavity. Moreover, we determine the Si+ ion to SiV center conversion yield
to and observe a 10-fold conversion yield increase by additional
electron irradiation. We extract inhomogeneously broadened ensemble emission
linewidths of GHz, and close to lifetime-limited single-emitter
transition linewidths down to MHz corresponding to -times
the natural linewidth. This demonstration of deterministic creation of
optically coherent solid-state single quantum systems is an important step
towards development of scalable quantum optical devices
Narrow-Linewidth Homogeneous Optical Emitters in Diamond Nanostructures via Silicon Ion Implantation
The negatively-charged silicon-vacancy (SiVâ) center in diamond is a bright source of indistinguishable single photons and a useful resource in quantum information protocols. Until now, SiVâ centers with narrow optical linewidths and small inhomogeneous distributions of SiVâ transition frequencies have only been reported in samples doped with silicon during diamond growth. We present a technique for producing implanted SiVâ centers with nearly lifetime-limited optical linewidths and a small inhomogeneous distribution. These properties persist after nanofabrication, paving the way for incorporation of high-quality SiVâ centers into nanophotonic devices.Physic
Cavity-Enhanced Photon Emission from a Single Germanium-Vacancy Center in a Diamond Membrane
The nitrogen-vacancy center in diamond has been explored extensively as a
light-matter interface for quantum information applications, however it is
limited by low coherent photon emission and spectral instability. Here, we
present a promising interface based on an alternate defect with superior
optical properties (the germanium-vacancy) coupled to a finesse
fiber cavity, resulting in a -fold increase
in the spectral density of emission. This work sets the stage for cryogenic
experiments, where we predict a measurable increase in the spontaneous emission
rate.Comment: 7 pages, 6 figure
Quantum interference of electromechanically stabilized emitters in nanophotonic devices
Photon-mediated coupling between distant matter qubits may enable secure
communication over long distances, the implementation of distributed quantum
computing schemes, and the exploration of new regimes of many-body quantum
dynamics. Nanophotonic devices coupled to solid-state quantum emitters
represent a promising approach towards realization of these goals, as they
combine strong light-matter interaction and high photon collection
efficiencies. However, the scalability of these approaches is limited by the
frequency mismatch between solid-state emitters and the instability of their
optical transitions. Here we present a nano-electromechanical platform for
stabilization and tuning of optical transitions of silicon-vacancy (SiV) color
centers in diamond nanophotonic devices by dynamically controlling their strain
environments. This strain-based tuning scheme has sufficient range and
bandwidth to alleviate the spectral mismatch between individual SiV centers.
Using strain, we ensure overlap between color center optical transitions and
observe an entangled superradiant state by measuring correlations of photons
collected from the diamond waveguide. This platform for tuning spectrally
stable color centers in nanophotonic waveguides and resonators constitutes an
important step towards a scalable quantum network
Why do sanctions need time to work? Adjustment, learning and anticipation
Economists disagree on the influence of time on the probability of success of economic sanctions. Some argue that it takes time to convince the sanction target. Others stress that economic adjustment will reduce incentives to comply. We seek to reconcile these different literatures, modelling the target's decision to comply as a function of both (anticipatory) economic adjustment and Bayesian learning. We show that sanctions which do not work instantaneously (ie there is neither political compliance nor economic adjustment) can work in the long run, but only if the learning effect dominates the adjustment effect. A sufficient condition for ultimate compliance is that (potential) sanction damage that cannot be avoided by adjustment in the long run exceeds the yield of misconduct
Strain engineering of the silicon-vacancy center in diamond
We control the electronic structure of the silicon-vacancy (SiV) color-center in diamond by changing its static strain environment with a nano-electro-mechanical system. This allows deterministic and local tuning of SiV optical and spin transition frequencies over a wide range, an essential step towards multiqubit networks. In the process, we infer the strain Hamiltonian of the SiV revealing large strain susceptibilities of order 1 PHz/strain for the electronic orbital states. We identify regimes where the spin-orbit interaction results in a large strain susceptibility of order 100 THz/strain for spin transitions, and propose an experiment where the SiV spin is strongly coupled to a nanomechanical resonator
An evidence-based approach to the use of telehealth in long-term health conditions: development of an intervention and evaluation through pragmatic randomised controlled trials in patients with depression or raised cardiovascular risk
Background: Health services internationally are exploring the potential of telehealth to support the
management of the growing number of people with long-term conditions (LTCs).
Aim: To develop, implement and evaluate new care programmes for patients with LTCs, focusing on
two common LTCs as exemplars: depression or high cardiovascular disease (CVD) risk.
Methods
Development: We synthesised quantitative and qualitative evidence on the effectiveness of telehealth for
LTCs, conducted a qualitative study based on interviews with patients and staff and undertook a postal
survey to explore which patients are interested in different forms of telehealth. Based on these studies we developed a conceptual model [TElehealth in CHronic disease (TECH) model] as a framework for the
development and evaluation of the Healthlines Service for patients with LTCs.
Implementation: The Healthlines Service consisted of regular telephone calls to participants from health
information advisors, supporting them to make behaviour change and to use tailored online resources.
Advisors sought to optimise participantsâ medication and to improve adherence.
Evaluation: The Healthlines Service was evaluated with linked pragmatic randomised controlled trials
comparing the Healthlines Service plus usual care with usual care alone, with nested process and economic
evaluations. Participants were adults with depression or raised CVD risk recruited from 43 general practices
in three areas of England. The primary outcome was response to treatment and the secondary outcomes
included anxiety (depression trial), individual risk factors (CVD risk trial), self-management skills, medication
adherence, perceptions of support, access to health care and satisfaction with treatment.
Trial results
Depression trial: In total, 609 participants were randomised and the retention rate was 86%. Response
to treatment [Patient Health Questionnaire 9-items (PHQ-9) reduction of â„ 5 points and score of < 10 after
4 months] was higher in the intervention group (27%, 68/255) than in the control group (19%, 50/270)
[odds ratio 1.7, 95% confidence interval (CI) 1.1 to 2.5; p = 0.02]. Anxiety also improved. Intervention
participants reported better access to health support, greater satisfaction with treatment and small
improvements in self-management, but not improved medication adherence.
CVD risk trial: In total, 641 participants were randomised and the retention rate was 91%. Response to
treatment (maintenance of/reduction in QRISKÂź2 score after 12 months) was higher in the intervention
group (50%, 148/295) than in the control group (43%, 124/291), which does not exclude a null effect
(odds ratio 1.3, 95% CI 1.0 to 1.9; p = 0.08). The intervention was associated with small improvements in
blood pressure and weight, but not smoking or cholesterol. Intervention participants were more likely to
adhere to medication, reported better access to health support and greater satisfaction with treatment,
but few improvements in self-management.
The Healthlines Service was likely to be cost-effective for CVD risk, particularly if the benefits are sustained,
but not for depression. The intervention was implemented largely as planned, although initial delays and
later disruption to delivery because of the closure of NHS Direct may have adversely affected participant
engagement.
Conclusion: The Healthlines Service, designed using an evidence-based conceptual model, provided modest health benefits and participants valued the better access to care and extra support provided.
This service was cost-effective for CVD risk but not depression. These findings of small benefits at extra
cost are consistent with previous pragmatic research on the implementation of comprehensive telehealth
programmes for LTCs
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