An as yet outstanding goal in quantum optics is the realization of fast optical nonlinearities at the single-photon level. This would allow for the implementation of optical devices with new ...functionalities such as single-photon switches/transistors or controlled-phase gates. Although nonlinear optics effects at the single-emitter level have been demonstrated in a number of systems, none of these experiments showed single-photon switching on ultrafast timescales. Here, we perform pulsed two-colour spectroscopy and demonstrate that, in a strongly coupled quantum dot-cavity system, the presence of a single photon on one of the fundamental polariton transitions can turn on light scattering on a transition from the first to the second Jaynes-Cummings manifold. The overall switching time of this single-photon all-optical switch is ∼50 ps. In addition, we use the single-photon nonlinearity to implement a pulse correlator. Our quantum dot-cavity system could form the building block of future high-bandwidth photonic networks operating in the quantum regime.
Strongly correlated photons on a chip Reinhard, Andreas; Volz, Thomas; Winger, Martin ...
Nature photonics,
02/2012, Letnik:
6, Številka:
2
Journal Article
Recenzirano
Optical nonlinearities at the single-photon level are key ingredients for future photonic quantum technologies. Prime candidates for the realization of the strong photon-photon interactions necessary ...for implementing quantum information processing tasks, as well as for studying strongly correlated photons in an integrated photonic device setting, are quantum dots embedded in photonic-crystal nanocavities. Here, we report strong quantum correlations between photons on picosecond timescales. We observe (i) photon antibunching upon resonant excitation of the lowest-energy polariton state, proving that the first cavity photon blocks the subsequent injection events, and (ii) photon bunching when the laser field is in two-photon resonance with the polariton eigenstates of the second Jaynes-Cummings manifold, demonstrating that two photons at this colour are more likely to be injected into the cavity jointly than they would otherwise. Together, these results demonstrate unprecedented strong single-photon nonlinearities, paving the way for the realization of a quantum optical Josephson interferometer or a single-photon transistor.
A key challenge for climate projection science is to serve the rapidly growing needs of impact and adaptation assessments (hereafter
risk assessments
) in an environment where there are substantial ...differences in the regional projections of climate models, an expanding number of potentially relevant climate model results, and a desire amongst many users to limit the number of future climate scenarios in their assessments. While it may be attractive to select a small number of climate models based on their ability to replicate current climate, there is no robust method for doing this. We outline and illustrate a method that addresses this challenge in a different way. The range of plausible future climates simulated by climate models is classified into a small set of Representative Climate Futures (RCFs) and the relative likelihood of these estimated. For each region, the RCFs are then used as a framework in which to classify more detailed information, such as available climate model and downscaled data sets. Researchers wishing to apply the RCFs in risk assessments can then choose to use a subset of RCFs, such as the “most likely”, “high risk” and “least change” cases for their impact system. Preparation and analysis of future climate data sets can therefore be confined to those models whose simulations best represent the selected RCFs. This significantly reduces the number of models involved, and potentially the effort required to undertake the risk assessment. Consistently applied within a region, RCFs, rather than individual climate models, can become the
boundary objects
which anchor discussion between the climate science and risk assessment communities, simplifying communication. Since the RCF descriptions need not change as new climate model results emerge, they can also provide a stable framework for assimilating risk assessments undertaken at different times with different sets of climate models. Systematic application of this approach requires various challenges to be addressed, such as robustly classifying future regional climates into a small set and estimating likelihoods.
In a coupled quantum-dot-nanocavity system, the photoluminescence from an off-resonance cavity mode exhibits strong quantum correlations with the quantum-dot transitions, even though its ...autocorrelation function is classical. Using new pump-power dependent photon-correlation measurements, we demonstrate that this seemingly contradictory observation that has so far defied an explanation stems from cascaded cavity photon emission in transitions between excited multiexciton states. The mesoscopic nature of quantum-dot confinement ensures the presence of a quasicontinuum of excitonic transitions, part of which overlaps with the cavity resonance.
To improve the quality of depression management, collaborative care models have been developed from the Chronic Care Model over the past 20 years. Collaborative care is a multicomponent, healthcare ...system-level intervention that uses case managers to link primary care providers, patients, and mental health specialists. In addition to case management support, primary care providers receive consultation and decision support from mental health specialists (i.e., psychiatrists and psychologists). This collaboration is designed to (1) improve routine screening and diagnosis of depressive disorders; (2) increase provider use of evidence-based protocols for the proactive management of diagnosed depressive disorders; and (3) improve clinical and community support for active client/patient engagement in treatment goal-setting and self-management.
A team of subject matter experts in mental health, representing various agencies and institutions, conceptualized and conducted a systematic review and meta-analysis on collaborative care for improving the management of depressive disorders. This team worked under the guidance of the Community Preventive Services Task Force, a nonfederal, independent, volunteer body of public health and prevention experts. Community Guide systematic review methods were used to identify, evaluate, and analyze available evidence.
An earlier systematic review with 37 RCTs of collaborative care studies published through 2004 found evidence of effectiveness of these models in improving depression outcomes. An additional 32 studies of collaborative care models conducted between 2004 and 2009 were found for this current review and analyzed. The results from the meta-analyses suggest robust evidence of effectiveness of collaborative care in improving depression symptoms (standardized mean difference SMD=0.34); adherence to treatment (OR=2.22); response to treatment (OR=1.78); remission of symptoms (OR=1.74); recovery from symptoms (OR=1.75); quality of life/functional status (SMD=0.12); and satisfaction with care (SMD=0.39) for patients diagnosed with depression (all effect estimates were significant).
Collaborative care models are effective in achieving clinically meaningful improvements in depression outcomes and public health benefits in a wide range of populations, settings, and organizations. Collaborative care interventions provide a supportive network of professionals and peers for patients with depression, especially at the primary care level.
This study identified predictors of seclusion or restraint use among licensed and/or accredited residential treatment centers (RTCs) for children and youth in the United States responding to a ...federally-sponsored survey of mental health services. 693 licensed and/or accredited child and adolescent RTCs responded to questions about the demographic and admission status of clients served on an identified date, services offered, size, ownership, funding, and their use of seclusion or restraint practices within the preceding 12 months. Logistic regression was used to determine factors predicting facility use of seclusion or restraint. A large majority of licensed and/or accredited child and adolescent RTCs (82 %) reported using seclusion or restraint in the prior year. Contrary to prior research, individual patient characteristics (percent of males, minorities, and involuntary admissions) did not predict the use of coercive techniques. Instead facility and funding variables accounted for approximately 27 % of the variance in the use of seclusion or restraint. Larger, privately-owned RTC’s funded primarily through public monies and which offered medication and programming for SED youth were more likely to endorse having used seclusion or restraint in the previous year. Despite visible policy and advocacy efforts to reduce seclusion and restraint use over the past decade, a majority of licensed and/or accredited RTCs for children and adolescents report using such practices. Findings emphasize the importance of examining facility-level variables in predicting their use, and highlight the disconnect between nationally espoused goals and current practices regarding coercive techniques in child and adolescent RTCs.
We demonstrate a deterministic approach to the implementation of solid-state cavity quantum electrodynamics (QED) systems based on a precise spatial and spectral overlap between a single ...self-assembled quantum dot and a photonic crystal membrane nanocavity. By fine-tuning nanocavity modes with a high quality factor into resonance with any given quantum dot exciton, we observed clear signatures of cavity QED (such as the Purcell effect) in all fabricated structures. This approach removes the major hindrances that had limited the application of solid-state cavity QED and enables the realization of experiments previously proposed in the context of quantum information processing.
Objective:This study identified and examined characteristics of mental health interventions listed in a registry of evidence-based behavioral health programs and practices.
Methods:Data were from the ...National Registry of Evidence-Based Programs and Practices (NREPP), which is sponsored by the Substance Abuse and Mental Health Services Administration. All mental health interventions posted as of May 2010 were reviewed.
Results:A total of 91 interventions were assessed. Over half (57%) focused on promoting mental health rather than on treating mental illness. The implementation materials and trainings for most interventions (52%) were proprietary. Analysis of NREPP's rated dimensions revealed that quality-of-research scores were significantly lower for interventions with exclusively proprietary materials, whereas readiness-for-dissemination scoreswere significantly lower for interventions with exclusively publicly available materials.
Conclusions:NREPP represents a practical tool for organizations seeking to initiate or expand their use of evidence-based services. Periodic studies of listed interventions may help to identify programmatic gaps in NREPP. (Psychiatric Services 62:303–305, 2011)
We show how cavity quantum electrodynamics using a tunable photonic crystal nanocavity in the strong-coupling regime can be used for single quantum dot spectroscopy. From the distinctive avoided ...crossings observed in the strongly coupled system we can identify the neutral and single positively charged exciton as well as the biexciton transitions. Moreover we are able to investigate the fine structure of those transitions and to identify a novel cavity mediated mixing of bright and dark exciton states, where the hyperfine interactions with lattice nuclei presumably play a key role. These results are enabled by a deterministic coupling scheme which allowed us to achieve unprecedented coupling strengths in excess of 150 microeV.
PDF
