Simple Phase Bias for Superconducting Circuits

A phase-bias tool, based on a trapped fluxoid in a ring, is proposed and demonstrated. It can provide arbitrary phase values and is simple to fabricate. The phase bias has been realized in two superconducting quantum interference devices, where the critical current versus magnetic flux is shown to be shifted by a \pi/2 and \pi.Comment: 5 pages, including 4 figures. Submitted to AP

QND measurement of a superconducting qubit in the weakly projective regime

Quantum state detectors based on switching of hysteretic Josephson junctions biased close to their critical current are simple to use but have strong back-action. We show that the back-action of a DC-switching detector can be considerably reduced by limiting the switching voltage and using a fast cryogenic amplifier, such that a single readout can be completed within 25 ns at a repetition rate of 1 MHz without loss of contrast. Based on a sequence of two successive readouts we show that the measurement has a clear quantum non-demolition character, with a QND fidelity of 75 %.Comment: submitted to PR

Josephson squelch filter for quantum nanocircuits

We fabricated and tested a squelch circuit consisting of a copper powder filter with an embedded Josephson junction connected to ground. For small signals (squelch-ON), the small junction inductance attenuates strongly from DC to at least 1 GHz, while for higher frequencies dissipation in the copper powder increases the attenuation exponentially with frequency. For large signals (squelch-OFF) the circuit behaves as a regular metal powder filter. The measured ON/OFF ratio is larger than 50dB up to 50 MHz. This squelch can be applied in low temperature measurement and control circuitry for quantum nanostructures such as superconducting qubits and quantum dots.Comment: Corrected and completed references 6,7,8. Updated some minor details in figure

De vruchten van de uitbreiding

De scepsis over een mogelijk overhaaste uitbreiding neemt toe. Welke effecten op consumptie en handel mogen worden verwacht

Low-crosstalk bifurcation detectors for coupled flux qubits

We present experimental results on the crosstalk between two AC-operated dispersive bifurcation detectors, implemented in a circuit for high-fidelity readout of two strongly coupled flux qubits. Both phase-dependent and phase-independent contributions to the crosstalk are analyzed. For proper tuning of the phase the measured crosstalk is 0.1 % and the correlation between the measurement outcomes is less than 0.05 %. These results show that bifurcative readout provides a reliable and generic approach for multi-partite correlation experiments.Comment: Copyright 2010 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Applied Physics Letters and may be found at http://link.aip.org/link/?apl/96/12350

Geometrical Defects in Josephson Junction Arrays

Dislocations and disclinations in a lattice of Josephson junctions will affect the dynamics of vortex excitations within the array. These defects effectively distort the space in which the excitations move and interact. The interaction energy between such defects and excitations are determined and vortex trajectories in twisted lattices are calculated. Finally, possible experiments observing these effects are presented.Comment: 26 pages including 5 figure

Antenatal corticosteroid therapy for foetal maturation in women with eclampsia and severe pre-eclampsia in a rural hospital in Western Tanzania

Contains fulltext : 171449.pdf (publisher's version ) (Open Access)BACKGROUND: Preterm birth is a major cause of neonatal mortality, especially in low and middle income countries. Antenatal corticosteroid therapy for foetal maturation could have a significant impact and therefore is often referred to as an important strategy to reduce neonatal mortality. A recently conducted large multinational trial showed that antenatal corticosteroids can have adverse effects in low income countries, but this is likely to depend on the specific setting. In our hospital preterm birth is only recognized in patients with severe maternal disease, due to physician-initiated delivery. Spontaneous preterm births are rarely seen in the hospital and often take place in the community or while on the road to a health facility. OBJECTIVE: To investigate the effects of antenatal corticosteroid therapy in a rural hospital in Tanzania. METHODS: A secondary analysis of a retrospective medical records study of women with severe pre-eclampsia and eclampsia performed in Ndala Hospital between July 2011 and December 2012. We used data on gestational age, birth weight, Apgar score, time between admission and birth, use of corticosteroids and maternal and foetal survival. Ethical clearance was obtained from the directorate of research and publications of the University of Dodoma (ref. UDOM/DRP/346). RESULTS: Thirty-six women with forty live foetuses were analysed. Twelve women (13 neonates) were given corticosteroids and could be compared to 24 women (27 neonates) who did not get corticosteroids. The incidence of fresh stillbirths (antenatal death) was 20 %. The 13 neonates who received corticosteroids had significantly smaller birth weight, longer interval between admission and delivery and poorer outcomes (stillbirth and neonatal death). An analysis of 24 neonates with a birth weight between 1.5 and 2.5 kg showed a trend toward better outcome in neonates who did not receive antenatal corticosteroid therapy. CONCLUSION: Small retrospective studies as these have a low level of evidence, but this study helped to gain more knowledge of local conditions affecting the effectiveness of antenatal corticosteroid therapy in our setting of a small rural hospital. Reliability of estimating gestational age, epidemiology of preterm birth, exposure to infections, foetal monitoring and quality of neonatal care are likely to influence the effect of antenatal corticosteroid therapy. Further larger prospective studies should be conducted to determine the exact preconditions of antenatal corticosteroid therapy in low-income countries. Until that time, the WHO precautions seem reasonable and audits and small observational studies like ours can help in assessing whether a specific hospital is suited for antenatal corticosteroid therapy

Association between surgical technique, adhesions and morbidity in women with repeat caesarean section:a retrospective study in a rural hospital in Western Tanzania

BACKGROUND: The worldwide incidence of birth by Caesarean Section (CS) is rising. Many births after a previous CS are by repeat surgery, either by an elective CS or after a failed trial of labour. Adhesion formation is associated with increased maternal morbidity in patients with repeat CSs. In spite of large-scale studies the relation between the incidence of adhesion formation and CS surgical technique is unclear. This study aims to assess maternal and neonatal morbidity and mortality after repeat CSs in a rural hospital in a low-income country (LIC) and to analyse the effect of surgical technique on the formation of adhesions. METHODS: A cross-sectional, retrospective medical records study of all women undergoing CS in Ndala Hospital in 2011 and 2012. RESULTS: Of the 3966 births, 450 were by CS (11.3%), of which 321 were 1st CS, 80 2nd CS, 36 3rd CS, 12 4th and one 5th CS (71, 18, 8, 3 and 0.2% respectively). Adhesions were considered to be severe in 56% of second CSs and 64% of third CSs. In 2nd CSs, adhesions were not associated with closure of the peritoneum at 1st CS, but were associated with the prior use of a midline skin incision. There was no increase in maternal morbidity when severe adhesions were present. Adverse neonatal outcome was more prevalent when severe adhesions were present, but this was statistically non-significant (16% vs 6%). CONCLUSIONS: Our results give insight into the practice of repeat CS in our rural hospital. Adhesions after CSs are common and occur more frequently after midline skin incision at 1st CS compared to a transverse incision. Reviewing local data is important to evaluate quality of care and to compare local outcomes to the literature