A scalable readout system for a superconducting adiabatic quantum optimization system

We have designed, fabricated and tested an XY-addressable readout system that is specifically tailored for the reading of superconducting flux qubits in an integrated circuit that could enable adiabatic quantum optimization. In such a system, the flux qubits only need to be read at the end of an adiabatic evolution when quantum mechanical tunneling has been suppressed, thus simplifying many aspects of the readout process. The readout architecture for an $N$-qubit adiabatic quantum optimization system comprises $N$ hysteretic dc SQUIDs and $N$ rf SQUID latches controlled by $2\sqrt{N} + 2$ bias lines. The latching elements are coupled to the qubits and the dc SQUIDs are then coupled to the latching elements. This readout scheme provides two key advantages: First, the latching elements provide exceptional flux sensitivity that significantly exceeds what may be achieved by directly coupling the flux qubits to the dc SQUIDs using a practical mutual inductance. Second, the states of the latching elements are robust against the influence of ac currents generated by the switching of the hysteretic dc SQUIDs, thus allowing one to interrogate the latching elements repeatedly so as to mitigate the effects of stochastic switching of the dc SQUIDs. We demonstrate that it is possible to achieve single qubit read error rates of $<10^{-6}$ with this readout scheme. We have characterized the system-level performance of a 128-qubit readout system and have measured a readout error probability of $8\times10^{-5}$ in the presence of optimal latching element bias conditions.Comment: Updated for clarity, final versio

A Growth Reference for Mid Upper Arm Circumference for Age among School Age Children and Adolescents, with Validation for Mortality in Two Cohorts

OBJECTIVES: To construct growth curves for mid-upper-arm circumference (MUAC)-for-age z score for 5-19 year olds that accord with the World Health Organization growth standards, and to evaluate their discriminatory performance for subsequent mortality. DESIGN: Growth curve construction and longitudinal cohort study. SETTING: United States and international growth data, and cohorts in Kenya, Uganda, and Zimbabwe. PARTICIPANTS The Health Examination Survey (HES)/National Health and Nutrition Examination Survey (NHANES) US population datasets (age 5-25 years), which were used to construct the 2007 WHO growth reference for body mass index in this age group, were merged with an imputed dataset matching the distribution of the WHO 2006 growth standards age 2-6 years. Validation data were from 685 HIV infected children aged 5-17 years participating in the Antiretroviral Research for Watoto (ARROW) trial in Uganda and Zimbabwe; and 1741 children aged 5-13 years discharged from a rural Kenyan hospital (3.8% HIV infected). Both cohorts were followed-up for survival during one year. MAIN OUTCOME MEASURES: Concordance with WHO 2006 growth standards at age 60 months and survival during one year according to MUAC-for-age and body mass index-for-age z scores. RESULTS: The new growth curves transitioned smoothly with WHO growth standards at age 5 years. MUAC-for-age z scores of −2 to −3 and less than−3, compared with −2 or more, was associated with hazard ratios for death within one year of 3.63 (95% confidence interval 0.90 to 14.7; P=0.07) and 11.1 (3.40 to 36.0; P<0.001), respectively, among ARROW trial participants; and 2.22 (1.01 to 4.9; P=0.04) and 5.15 (2.49 to 10.7; P<0.001), respectively, among Kenyan children after discharge from hospital. The AUCs for MUAC-for-age and body mass index-for-age z scores for discriminating subsequent mortality were 0.81 (95% confidence interval 0.70 to 0.92) and 0.75 (0.63 to 0.86) in the ARROW trial (absolute difference 0.06, 95% confidence interval −0.032 to 0.16; P=0.2) and 0.73 (0.65 to 0.80) and 0.58 (0.49 to 0.67), respectively, in Kenya (absolute difference in AUC 0.15, 0.07 to 0.23; P=0.0002). CONCLUSIONS: The MUAC-for-age z score is at least as effective as the body mass index-for-age z score for assessing mortality risks associated with undernutrition among African school aged children and adolescents. MUAC can provide simplified screening and diagnosis within nutrition and HIV programmes, and in research

A growth reference for mid upper arm circumference for age among school age children and adolescents, and validation for mortality: growth curve construction and longitudinal cohort study

Objectives Worldwide, school age children and adolescents are vulnerable to conflict and food insecurity and HIV-infected children are increasingly surviving into adolescence. WHO recommends assessing acute malnutrition in this age group using body mass index-for-age Z scores (BMIz). For under-fives, mid upper arm circumference (MUAC) is the mainstay of community diagnosis of acute malnutrition, is simple to perform and predicts survival better than weight-for-height Z scores. MUAC is little-used in older children and adolescents because there is no accepted international reference. This study aimed to construct growth curves for MUAC-for-age Z score (MUACz) for 5-19 year olds that accord with WHO Growth Standards, and evaluate their discriminatory performance for subsequent mortality. Design The HES/NHANES US population datasets (age 5-25 years), which were used to construct the 2007 WHO Growth Reference for BMI in this age group, were merged with an imputed dataset matching the distribution of the WHO 2006 Growth Standards age 2-6 years. To construct standardised growth curves, we used Generalized Additive Models for Location, Scale and Shape with Box-Cox Cole Green transformation and penalized B-spline smoothing. Validation for subsequent mortality in two cohorts was done using Cox proportional hazards models for pre-defined MUACz and BMIz thresholds, with age, gender and HIV status as covariates; and estimation of the area under receiver-operating characteristic curves (AUC). Participants Validation data were from 685 HIV-infected children age 5¬–17 years participating in the ARROW trial in Uganda and Zimbabwe; and 1,741 children age 5–13 years discharged from a rural Kenyan hospital (3.8% HIV-infected). Both cohorts were followed up for survival during one year. Main outcome measures Concordance with WHO 2006 Growth Standards at age 60 months and survival during one year according to MUACz and BMIz. Results The new growth curves transitioned smoothly with WHO Growth Standards at age 5 years. MUACz of -2 to -3 and <-3, compared with ≥-2, was associated with hazard ratios for death within one year of 3.63 (95%CI 0.90 to 14.7; P=0.07) and 11.1 (95%CI 3.40 to 36.0; P<0.0001) respectively among ARROW trial participants; and 2.22 (95%CI 1.01 to 4.9; P=0.04) and 5.15 (95%CI 2.49 to 10.7; P<0.0001) respectively among Kenyan children after discharge from hospital. The AUCs for MUACz and BMIz for discriminating subsequent mortality were 0.81 (95%CI 0.70 to 0.92) and 0.75 (95%CI 0.63 to 0.86) in the ARROW trial (absolute difference 0.06 (95% CI -0.032 to 0.16; P=0.2); and 0.73 (95%CI 0.65 to 0.80) and 0.58 (95% CI 0.49 to 0.67) respectively in Kenya (absolute difference in AUC 0.15 (95% CI 0.07 to 0.23; P=0.0002). Conclusions MUACz is at least as effective as BMIz for assessing mortality risks associated with undernutrition among African school-aged children and adolescents. MUAC can provide simplified screening and diagnosis within nutrition and HIV programmes, and in research

Profile: The Kilifi Health and Demographic Surveillance System (KHDSS).

The Kilifi Health and Demographic Surveillance System (KHDSS), located on the Indian Ocean coast of Kenya, was established in 2000 as a record of births, pregnancies, migration events and deaths and is maintained by 4-monthly household visits. The study area was selected to capture the majority of patients admitted to Kilifi District Hospital. The KHDSS has 260 000 residents and the hospital admits 4400 paediatric patients and 3400 adult patients per year. At the hospital, morbidity events are linked in real time by a computer search of the population register. Linked surveillance was extended to KHDSS vaccine clinics in 2008. KHDSS data have been used to define the incidence of hospital presentation with childhood infectious diseases (e.g. rotavirus diarrhoea, pneumococcal disease), to test the association between genetic risk factors (e.g. thalassaemia and sickle cell disease) and infectious diseases, to define the community prevalence of chronic diseases (e.g. epilepsy), to evaluate access to health care and to calculate the operational effectiveness of major public health interventions (e.g. conjugate Haemophilus influenzae type b vaccine). Rapport with residents is maintained through an active programme of community engagement. A system of collaborative engagement exists for sharing data on survival, morbidity, socio-economic status and vaccine coverage

Entanglement in a quantum annealing processor

Entanglement lies at the core of quantum algorithms designed to solve problems that are intractable by classical approaches. One such algorithm, quantum annealing (QA), provides a promising path to a practical quantum processor. We have built a series of scalable QA processors consisting of networks of manufactured interacting spins (qubits). Here, we use qubit tunneling spectroscopy to measure the energy eigenspectrum of two- and eight-qubit systems within one such processor, demonstrating quantum coherence in these systems. We present experimental evidence that, during a critical portion of QA, the qubits become entangled and that entanglement persists even as these systems reach equilibrium with a thermal environment. Our results provide an encouraging sign that QA is a viable technology for large-scale quantum computing.Comment: 13 pages, 8 figures, contact corresponding author for Supplementary Informatio

Sign- and magnitude-tunable coupler for superconducting flux qubits

We experimentally confirm the functionality of a coupling element for flux-based superconducting qubits, with a coupling strength $J$ whose sign and magnitude can be tuned {\it in situ}. To measure the effective $J$, the groundstate of a coupled two-qubit system has been mapped as a function of the local magnetic fields applied to each qubit. The state of the system is determined by directly reading out the individual qubits while tunneling is suppressed. These measurements demonstrate that $J$ can be tuned from antiferromagnetic through zero to ferromagnetic.Comment: Updated text and figure

Structure, Time Propagation and Dissipative Terms for Resonances

For odd anharmonic oscillators, it is well known that complex scaling can be used to determine resonance energy eigenvalues and the corresponding eigenvectors in complex rotated space. We briefly review and discuss various methods for the numerical determination of such eigenvalues, and also discuss the connection to the case of purely imaginary coupling, which is PT-symmetric. Moreover, we show that a suitable generalization of the complex scaling method leads to an algorithm for the time propagation of wave packets in potentials which give rise to unstable resonances. This leads to a certain unification of the structure and the dynamics. Our time propagation results agree with known quantum dynamics solvers and allow for a natural incorporation of structural perturbations (e.g., due to dissipative processes) into the quantum dynamics.Comment: 14 pages; LaTeX; minor change