146 research outputs found

    Sensitive radio-frequency read-out of quantum dots using an ultra-low-noise SQUID amplifier

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    Fault-tolerant spin-based quantum computers will require fast and accurate qubit readout. This can be achieved using radio-frequency reflectometry given sufficient sensitivity to the change in quantum capacitance associated with the qubit states. Here, we demonstrate a 23-fold improvement in capacitance sensitivity by supplementing a cryogenic semiconductor amplifier with a SQUID preamplifier. The SQUID amplifier operates at a frequency near 200 MHz and achieves a noise temperature below 600 mK when integrated into a reflectometry circuit, which is within a factor 120 of the quantum limit. It enables a record sensitivity to capacitance of 0.07 aF/ \sqrt{Hz}. The setup is used to acquire charge stability diagrams of a gate-defined double quantum dot in a short time with a signal-to-noise ration of about 38 in 1 ÎŒs of integration time

    Photon-assisted tunneling and charge dephasing in a carbon nanotube double quantum dot

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    We report microwave-driven photon-assisted tunneling in a suspended carbon nanotube double quantum dot. From the resonant linewidth at a temperature of 13 mK, the charge-dephasing time is determined to be 280 ± 30 ps. The linewidth is independent of driving frequency, but increases with increasing temperature. The moderate temperature dependence is inconsistent with expectations from electron-phonon coupling alone, but consistent with charge noise arising in the device. The extracted level of charge noise is comparable with that expected from previous measurements of a valley-spin qubit, where it was hypothesized to be the main cause of qubit decoherence. Our results suggest a possible route towards improved valley-spin qubits

    Factors associated with preterm delivery and low birth weight: a study from rural Maharashtra, India

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    Background: Although preterm delivery and low birth weight (LBW) have been studied in India, findings may not be generalisable to rural areas such as the Marathwada region of Maharashtra state. There is limited information available on maternal and child health indicators from this region. We aimed to present some local estimates of preterm delivery and LBW in the Osmanabad district of Marathwada and assess available maternal risk factors. Methods: The study used routinely collected data on all in-hospital births in the maternity department of Halo Medical Foundation’s hospital from 1 (st )January 2008 to 31 (st )December 2014. Multivariable logistic regression analysis provided odds ratios (OR) with 95% confidence intervals (CI) for preterm delivery and LBW according to each maternal risk factor. Results: We analysed 655 live births, of which 6.1% were preterm deliveries. Of the full term births (N=615), 13.8% were LBW (<2.5 kilograms at birth). The odds of preterm delivery were three times higher (OR=3.23, 95% CI 1.36 to 7.65) and the odds of LBW were double (OR=2.03, 95% CI 1.14 to 3.60) among women <22 years of age compared with older women. The odds of both preterm delivery and LBW were reduced in multigravida compared with primigravida women regardless of age. Anaemia (Hb<11g/dl), which was prevalent in 91% of women tested, was not significantly related to these birth outcomes. Conclusions: The odds of preterm delivery and LBW were much higher in mothers under 22 years of age in this rural Indian population. Future studies should explore other related risk factors and the reasons for poor birth outcomes in younger mothers in this population, to inform the design of appropriate public health policies that address this issue

    Hyperfine and spin-orbit coupling effects on decay of spin-valley states in a carbon nanotube

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    The decay of spin-valley states is studied in a suspended carbon nanotube double quantum dot via leakage current in Pauli blockade and via dephasing and decoherence of a qubit. From the magnetic field dependence of the leakage current, hyperfine and spin-orbit contributions to relaxation from blocked to unblocked states are identified and explained quantitatively by means of a simple model. The observed qubit dephasing rate is consistent with the hyperfine coupling strength extracted from this model and inconsistent with dephasing from charge noise. However, the qubit coherence time, although longer than previously achieved, is probably still limited by charge noise in the device

    Resonant optomechanics with a vibrating carbon nanotube and a radio-frequency cavity

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    In an optomechanical setup, the coupling between cavity and resonator can be increased by tuning them to the same frequency. We study this interaction between a carbon nanotube resonator and a radiofrequency tank circuit acting as a cavity. In this resonant regime, the vacuum optomechanical coupling is enhanced by the dc voltage coupling the cavity and the mechanical resonator. Using the cavity to detect the nanotube’s motion, we observe and simulate interference between mechanical and electrical oscillations. We measure the mechanical ring down and show that further improvements to the system could enable the measurement of mechanical motion at the quantum limit

    Traditional birth attendants lack basic information on HIV and safe delivery practices in rural Mysore, India

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    <p>Abstract</p> <p>Background</p> <p>There is little research on HIV awareness and practices of traditional birth attendants (TBA) in India. This study investigated knowledge and attitudes among rural TBA in Karnataka as part of a project examining how traditional birth attendants could be integrated into prevention-of-mother-to-child transmission of HIV (PMTCT) programs in India.</p> <p>Methods</p> <p>A cross-sectional survey was conducted between March 2008 and January 2009 among TBA in 144 villages in Mysore <it>Taluk</it>, Karnataka. Following informed consent, TBA underwent an interviewer-administered questionnaire in the local language of <it>Kannada </it>on practices and knowledge around birthing and HIV/PMTCT.</p> <p>Results</p> <p>Of the 417 TBA surveyed, the median age was 52 years and 96% were Hindus. A majority (324, 77.7%) had no formal schooling, 88 (21.1%) had up to 7 years and 5 (1%) had more than 7 yrs of education. Only 51 of the 417 TBA (12%) reported hearing about HIV/AIDS. Of those who had heard about HIV/AIDS, only 36 (72%) correctly reported that the virus could be spread from mother to child; 37 (74%) identified unprotected sex as a mode of transmission; and 26 (51%) correctly said healthy looking people could spread HIV. Just 22 (44%) knew that infected mothers could lower the risk of transmitting the virus to their infants. An overwhelming majority of TBA (401, 96.2%) did not provide antenatal care to their clients. Over half (254, 61%) said they would refer the woman to a hospital if she bled before delivery, and only 53 (13%) felt referral was necessary if excessive bleeding occurred after birth.</p> <p>Conclusions</p> <p>Traditional birth attendants will continue to play an important role in maternal child health in India for the foreseeable future. This study demonstrates that a majority of TBA lack basic information about HIV/AIDS and safe delivery practices. Given the ongoing shortage of skilled birth attendance in rural areas, more studies are needed to examine whether TBA should be trained and integrated into PMTCT and maternal child health programs in India.</p

    Cost of hospitalization for childbirth in India: how equitable it is in the post-NRHM era?

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    BACKGROUND AND OBJECTIVE: Information on out-of-pocket (OOP) expenditure during childbirth in public and private health facilities in India is needed to make rational decisions for improving affordability to maternal care services. We undertook this study to evaluate the OOP expenditure due to hospitalization from childbirth and its impact on households. METHODS: This is a secondary data analysis of a nationwide household survey by the National Sample Survey Organization in 2014. The survey reported health service utilization and health care related expenditure by income quintiles and type of health facility. The recall period for hospitalization expenditure was 365 days. OOP expenditure amounting to more than 10% of annual consumption expenditure was termed as catastrophic. RESULTS: Median expenditure per episode of hospitalisation due to childbirth was US$54. The expenditure incurred was about six times higher among the richest quintile compared to the poorest quintile. Median private sector OOP hospitalization expenditure was nearly nine times higher than in the public sector. Hospitalization in a private sector facility leads to a significantly higher prevalence of catastrophic expenditure than hospitalization in a public sector (60% vs. 7%). Indirect cost (43%) constituted the largest share in the total expenditure in public sector hospitalizations. Urban residence, poor wealth quintile, residing in eastern and southern regions of India and delivery in private hospital were significantly associated with catastrophic expenditure. CONCLUSIONS: We strongly recommend cash transfer schemes with effective pro-poor targeting to reduce the impact of catastrophic expenditure. Strengthening of public health facilities is required along with private sector regulation
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