Probing Decoherence with Electromagnetically Induced Transparency in Superconductive Quantum Circuits

Superconductive quantum circuits (SQCs) comprise quantized energy levels that may be coupled via microwave electromagnetic fields. Described in this way, one may draw a close analogy to atoms with internal (electronic) levels coupled by laser light fields. In this Letter, we present a superconductive analog to electromagnetically induced transparency (S-EIT) that utilizes SQC designs of present day experimental consideration. We discuss how S-EIT can be used to establish macroscopic coherence in such systems and, thereby, utilized as a sensitive probe of decoherence.Comment: 5 pages, 3 figure

Dual and triple therapy to prevent mother-to-child transmission of HIV in a resource-limited setting – lessons from a South African programme

Objective. To determine outcomes of pregnant women and their infants at McCord Hospital in Durban, South Africa, where dual and triple therapy to reduce HIV vertical transmission have been used since 2004 despite national guidelines recommending simpler regimens. Method. We retrospectively examined records of all pregnant women attending McCord Hospital for their first antenatal visit between 1 March 2004 and 28 February 2007. Uptake of HIV testing and HIV prevalence were determined, and clinical, immunological and virological outcomes of HIV-positive women and their infants, followed through to 6 months after delivery, were described. Results. The antenatal clinic was attended by 5 303 women; 4 891 (92%) had an HIV test, and 703 (14%) were HIV positive. The HIV-positive women were subsequently followed up: 653 (93%) received antiretroviral therapy or prophylaxis, including 424 (60%) who received triple therapy. Of the 699 live babies delivered, 661 (94%) received prophylaxis. At 6 weeks 571 babies (82%) were brought back for HIV testing; 16 (2.8%) were HIV positive. After 6 months, only 150 women (21%) were receiving follow-up care at the adult HIV clinic. Conclusion. Where a tailored approach to prevention of motherto-child transmission (PMTCT) is used, which attempts to maximise available technology and resources, good short-term transmission outcomes can be achieved. However, longer-term follow-up of mothers’ and babies’ health presents a challenge. Successful strategies to link women to ongoing care are crucial to sustain the gains of PMTCT programmes

Impact of time-ordered measurements of the two states in a niobium superconducting qubit structure

Measurements of thermal activation are made in a superconducting, niobium Persistent-Current (PC) qubit structure, which has two stable classical states of equal and opposite circulating current. The magnetization signal is read out by ramping the bias current of a DC SQUID. This ramping causes time-ordered measurements of the two states, where measurement of one state occurs before the other. This time-ordering results in an effective measurement time, which can be used to probe the thermal activation rate between the two states. Fitting the magnetization signal as a function of temperature and ramp time allows one to estimate a quality factor of 10^6 for our devices, a value favorable for the observation of long quantum coherence times at lower temperatures.Comment: 14 pages, 4 figure

DC measurements of macroscopic quantum levels in a superconducting qubit structure with a time-ordered meter

DC measurements are made in a superconducting, persistent current qubit structure with a time-ordered meter. The persistent-current qubit has a double-well potential, with the two minima corresponding to magnetization states of opposite sign. Macroscopic resonant tunneling between the two wells is observed at values of energy bias that correspond to the positions of the calculated quantum levels. The magnetometer, a Superconducting Quantum Interference Device (SQUID), detects the state of the qubit in a time-ordered fashion, measuring one state before the other. This results in a different meter output depending on the initial state, providing different signatures of the energy levels for each tunneling direction. From these measurements, the intrawell relaxation time is found to be about 50 microseconds.Comment: 17 pages, 7 figure

South Africans with Recent Pregnancy Rarely Know Partner’s HIV Serostatus: Implications for Serodiscordant Couples Interventions

Background: Implementation of safer conception strategies requires knowledge of partner HIV-serostatus. We recruited women and men in a high HIV-prevalence setting for a study to assess periconception risk behavior among individuals reporting HIV-serodiscordant partnerships. We report screening data from that study with the objective of estimating the proportion of individuals who are aware that they are in an HIV-serodiscordant relationship at the time of conception. Methods: We screened women and men attending antenatal and antiretroviral clinics in Durban, South Africa for enrollment in a study of periconception risk behavior among individuals with serodiscordant partners. Screening questionnaires assessed for study eligibility including age 18–45 years (for women) or at least 18 years of age (for men), pregnancy in past year (women) or partner pregnancy in the past 3 years (men), HIV status of partner for recent pregnancy, participant’s HIV status, and infected partner’s HIV status having been known before the referent pregnancy. Results: Among 2620 women screened, 2344 (90%) met age and pregnancy criteria and knew who fathered the referent pregnancy. Among those women, 963 (41%) did not know the pregnancy partner’s HIV serostatus at time of screening. Only 92 (4%) reported knowing of a serodiscordant partnership prior to pregnancy. Among 1166 men screened, 225 (19%) met age and pregnancy criteria. Among those men, 71 (32%) did not know the pregnancy partner’s HIV status and only 30 (13%) reported knowing of a serodiscordant partnership prior to pregnancy. Conclusions: In an HIV-endemic setting, awareness of partner HIV serostatus is rare. Innovative strategies to increase HIV testing and disclosure are required to facilitate HIV prevention interventions for serodiscordant couples

BlinkML: Efficient Maximum Likelihood Estimation with Probabilistic Guarantees

The rising volume of datasets has made training machine learning (ML) models a major computational cost in the enterprise. Given the iterative nature of model and parameter tuning, many analysts use a small sample of their entire data during their initial stage of analysis to make quick decisions (e.g., what features or hyperparameters to use) and use the entire dataset only in later stages (i.e., when they have converged to a specific model). This sampling, however, is performed in an ad-hoc fashion. Most practitioners cannot precisely capture the effect of sampling on the quality of their model, and eventually on their decision-making process during the tuning phase. Moreover, without systematic support for sampling operators, many optimizations and reuse opportunities are lost. In this paper, we introduce BlinkML, a system for fast, quality-guaranteed ML training. BlinkML allows users to make error-computation tradeoffs: instead of training a model on their full data (i.e., full model), BlinkML can quickly train an approximate model with quality guarantees using a sample. The quality guarantees ensure that, with high probability, the approximate model makes the same predictions as the full model. BlinkML currently supports any ML model that relies on maximum likelihood estimation (MLE), which includes Generalized Linear Models (e.g., linear regression, logistic regression, max entropy classifier, Poisson regression) as well as PPCA (Probabilistic Principal Component Analysis). Our experiments show that BlinkML can speed up the training of large-scale ML tasks by 6.26x-629x while guaranteeing the same predictions, with 95% probability, as the full model.Comment: 22 pages, SIGMOD 201

Compound Semiconductor Materials and Devices

Contains table of contents for Part I, table of contents for Section 1, an introduction, reports on fourteen research projects and a list of publications.Defense Advanced Research Projects Agency/National Center for Integrated Photonics TechnologyJoint Services Electronics Program Grant DAAH04-95-1-0038MIT Lincoln LaboratoryNational Science Foundation Graduate FellowshipU.S. Navy - Office of Naval ResearchAT&T Bell Laboratories FellowshipU.S. Army - Ft. MeadeNTT CorporationNational Science FoundationLockheed-Martin Corporatio

Supporting HIV prevention and reproductive goals in an HIV-endemic setting: taking safer conception services from policy to practice in South Africa

INTRODUCTION: Safer conception care encompasses HIV care, treatment and prevention for persons living with HIV and their partners who desire children. In 2012, South Africa endorsed a progressive safer conception policy supporting HIV-affected persons to safely meet reproductive goals. However, aside from select research-supported clinics, widespread implementation has not occurred. Using South Africa as a case study, we identify key obstacles to policy implementation and offer recommendations to catalyse expansion of these services throughout South Africa and further afield. DISCUSSION: Four key implementation barriers were identified by combining authors’ safer conception service delivery experiences with available literature. First, strategic implementation frameworks stipulating where, and by whom, safer conception services should be provided are needed. Integrating safer conception services into universal test-and-treat (UTT) and elimination-of-mother-to-child-transmission (eMTCT) priority programmes would support HIV testing, ART initiation and management, viral suppression and early antenatal/eMTCT care engagement goals, reducing horizontal and vertical transmissions. Embedding measurable safer conception targets into these priority programmes would ensure accountability for implementation progress. Second, facing an organizational clinic culture that often undermines clients’ reproductive rights, healthcare providers’ (HCP) positive experiences with eMTCT and enthusiasm for UTT provide opportunities to shift facilitylevel and individual attitudes in favour of safer conception provision. Third, safer conception guidelines have not been incorporated into HCP training. Combining safer conception with “test-and-treat” training would efficiently ensure that providers are better equipped to discuss clients’ reproductive goals and support safer conception practices. Lastly, HIVaffected couples remain largely unaware of safer conception strategies. HIV-affected populations need to be mobilized to engage with safer conception options alongside other HIV-related healthcare services. CONCLUSION: Key barriers to widespread safer conception service provision in South Africa include poor translation of policy into practical and measurable implementation plans, inadequate training and limited community engagement. South Africa should leverage the momentum and accountability associated with high priority UTT and eMTCT programmes to reinvigorate implementation efforts by incorporating safer conception into implementation and monitoring frameworks and associated HCP training and community engagement activities. South Africa’s experiences should be used to inform policy development and implementation processes in other HIV high-burden countries.IS