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

Partial-measurement back-action and non-classical weak values in a superconducting circuit

We realize indirect partial measurement of a transmon qubit in circuit quantum electrodynamics by interaction with an ancilla qubit and projective ancilla measurement with a dedicated readout resonator. Accurate control of the interaction and ancilla measurement basis allows tailoring the measurement strength and operator. The tradeoff between measurement strength and qubit back-action is characterized through the distortion of a qubit Rabi oscillation imposed by ancilla measurement in different bases. Combining partial and projective qubit measurements, we provide the solid-state demonstration of the correspondence between a non-classical weak value and the violation of a Leggett-Garg inequality.Comment: 5 pages, 4 figures, and Supplementary Information (8 figures

Bilan du carbone dans le lagunage anaérobie appliqué sous climat méditerranéen

Ce travail a porté sur l'application du lagunage anaérobie pour le traitement primaire des eaux résiduaires urbaines sous climat méditerranéen. Il a été réalisé sur les lagunes anaérobies de l' Ecosite de Mèze (Hérault, France). Les lagunes anaérobies constituent un traitement primaire satisfaisant avec des rendements moyens de 55% pour les MES et 30% pour la DBO5, pour une faible emprise au sol. Le taux d'accumulation des boues est de seulement 0,017 m3 /EH.an, notamment du fait de l'efficacité de la dégradation anaérobie. L'équilibre du métabolisme anaérobie des boues est atteint après un an de fonctionnement. L'accumulation des boues se fait alors de façon saisonnière avec une forte accumulation en hiver et une digestion du stock en été. Cette évolution est liée à l'influence de la température sur la méthanogénèse. La production de biogaz (83% CH4) a pu être mesurée par des collecteurs à gaz mis au point pour cette étude et dépend également fortement de la température. Le bilan du carbone montre que 74% du carbone organique épuré est converti en CH4, 13% en carbone inorganique dissous et seulement 15% est stocké dans les boues. Toutefois, les lagunes anaérobies présentent un risque de créer des nuisances olfactives dues à l'émission de H2 S.This project examined the application of anaerobic ponds for the primary treatment of urban wastewater under a Mediterranean climate. The objectives of the study were to determine removal performances and to study sludge accumulation and the production of biogas. Together, these results allowed us to calculate the carbon mass balance in the anaerobic ponds.This work was carried out in the two large primary anaerobic ponds of the waste stabilization pond system at the Ecosite of Mèze (Hérault, France), treating domestic wastewater for 13,800 person-equivalents (PE). Anaerobic ponds were 5,000 m3 in volume, 3.1 m in depth and presented a retention time of 4.6 d with a mean volumetric organic loading of 83 g BOD5 /m3 ×d× The characteristics of the influent and effluent (including: suspended solids (SS); chemical oxygen demand (COD); biological oxygen demand (BOD5); bicarbonate (HCO3 -); total organic carbon (TOC); and volatile fatty acids (VFA)) were determined twice-monthly. The volume of sludge and its characteristics (including: SS; volatile solids (VS); TOC; and VFA) were measured monthly. The production of biogas and its composition (CH4, CO2, H2 S) were measured with gas collectors specially developed for this study.Results showed that the anaerobic ponds constituted a good primary treatment with mean removal rates of 55% for SS, 30% for BOD and 22% for COD. Removal performances were relatively constant over the year. Indeed, removal rates were essentially due to the removal of particulate organic matter by sedimentation. Anaerobic degradation occurred essentially in the sludge layer and the removal of soluble COD was low.The study of sludge characteristics showed that anaerobic digestion equilibrium was reached after one year of operation. The beginning of methanogenesis could be observed by the decrease in the concentration of volatile fatty acids. The accumulation of sludge showed seasonal variation with an important accumulation in winter and the digestion of the accumulated stock in summer. This evolution could be related to the influence of temperature on methanogenesis. The mean rate of sludge accumulation was only 3.8 g SS/P-E×d or 0.017 m3/P-E×yr. This rate was significantly lower than for the primary settling tank (50-60 g SS/P-E×d) and for the facultative ponds (0.085 m3 /P-E×yr) due to the intensive anaerobic degradation.The production of biogas was measured by gas collectors specially developed for this study. The biogas contained essentially CH4 (83%); CO2 was less than 4% because it dissolved in the water column and was converted into bicarbonate alkalinity. The concentration of H2 S was less than 1% (between 75 and 4770 ppm) but was the cause of unpleasant odours. The biogas production rate was strongly dependent on temperature. A non-linear relationship was obtained (Ebiogas=4.8451 × e0.1203T, r2=0.92, n=16). The mean annual biogas production rate was calculated to be 49 L/m2 ×d. Seasonal variation in the biogas production rate could be related to seasonal variations in sludge accumulation.The carbon mass balance showed that 74% of the removed organic carbon was converted into CH4, 13% into dissolved inorganic carbon (bicarbonates) and only 15% was stored in sludge. The mass balance was well equilibrated and did not show the entry of atmospheric CO2, which occurs in aerobic ponds where CO2 is used by algae to produce their cell biomass. In an anaerobic pond, the low production of sludge was due to the efficiency of the anaerobic degradation but also to the low internal biomass production.To conclude, the use of a primary anaerobic pond was advantageous and permitted a reduction in the required surface area for a waste stabilization pond system. This process produced effluent for secondary treatment in a facultative pond with essentially the removal of the particulate organic matter. However, However, anaerobic ponds may cause odor problems linked to the emission of H2 S

Interqubit coupling mediated by a high-excitation-energy quantum object

We consider a system composed of two qubits and a high-excitation-energy quantum object used to mediate coupling between the qubits. We treat the entire system quantum mechanically and analyze the properties of the eigenvalues and eigenstates of the total Hamiltonian. After reproducing well-known results concerning the leading term in the mediated coupling, we obtain an expression for the residual coupling between the qubits in the off state. We also analyze the entanglement between the three objects, i.e. the two qubits and the coupler, in the eigenstates of the total Hamiltonian. Although we focus on the application of our results to the recently realized parametric-coupling scheme with two qubits, we also discuss extensions of our results to harmonic-oscillator couplers, couplers that are near resonance with the qubits and multi-qubit systems. In particular, we find that certain errors that are absent for a two-qubit system arise when dealing with multi-qubit systems.Comment: 15 pages (two-column

MRI measures of middle cerebral artery diameter in conscious humans during simulated orthostasis.

BACKGROUND AND PURPOSE: The relationship between middle cerebral artery (MCA) flow velocity (CFV) and cerebral blood flow (CBF) is uncertain because of unknown vessel diameter response to physiological stimuli. The purpose of this study was to directly examine the effect of a simulated orthostatic stress (lower body negative pressure [LBNP]) as well as increased or decreased end-tidal carbon dioxide partial pressure (P(ET)CO(2)) on MCA diameter and CFV. METHODS: Twelve subjects participated in a CO(2) manipulation protocol and/or an LBNP protocol. In the CO(2) manipulation protocol, subjects breathed room air (normocapnia) or 6% inspired CO(2) (hypercapnia), or they hyperventilated to approximately 25 mm Hg P(ET)CO(2) (hypocapnia). In the LBNP protocol, subjects experienced 10 minutes each of -20 and -40 mm Hg lower body suction. CFV and diameter of the MCA were measured by transcranial Doppler and MRI, respectively, during the experimental protocols. RESULTS: Compared with normocapnia, hypercapnia produced increases in both P(ET)CO(2) (from 36+/-3 to 40+/-4 mm Hg, P CONCLUSIONS: Under the conditions of this study, changes in MCA diameter were not detected. Therefore, we conclude that relative changes in CFV were representative of changes in CBF during the physiological stimuli of moderate LBNP or changes in P(ET)CO(2)

Role of relaxation in the quantum measurement of a superconducting qubit using a nonlinear oscillator

We analyze the relaxation of a superconducting flux qubit during measurement. The qubit state is measured with a nonlinear oscillator driven across the threshold of bifurcation, acting as a switching dispersive detector. This readout scheme is of quantum non-demolition type. Two successive readouts are used to analyze the evolution of the qubit and the detector during the measurement. We introduce a simple transition rate model to characterize the qubit relaxation and the detector switching process. Corrected for qubit relaxation the readout fidelity is at least 95%. Qubit relaxation strongly depends on the driving strength and the state of the oscillator.Comment: 4 pages, 4 figure

Effect of a 6-month brisk walking program on walking endurance in sedentary and physically deconditioned women aged 60 or older: A randomized trial

International audienceBACKGROUND:Walking endurance is a predictor of healthy ageing.OBJECTIVE:To examine if a 6-month brisk walking program can increase walking endurance in sedentary and physically deconditioned older women.TRIAL DESIGN:Randomized controlled trial.SETTING:Women recruited from public meetings aimed at promoting physical activity in women aged 60 or older.SUBJECTS:121 women aged 65.7 ± 4.3 years, with sedentary lifestyle (Physical Activity Questionnaire for the Elderly score 46%) were those with baseline lowest values of 6MWD (p=0.001) and highest values of body mass index (BMI) (p<0.01).CONCLUSION:Present results support recommendation that brisk walking programs should be encouraged to improve walking endurance in physically deconditioned women aged 60 or older, especially in those with high BMI