Improved Superconducting Qubit Readout by Qubit-Induced Nonlinearities

In dispersive readout schemes, qubit-induced nonlinearity typically limits the measurement fidelity by reducing the signal-to-noise ratio (SNR) when the measurement power is increased. Contrary to seeing the nonlinearity as a problem, here we propose to use it to our advantage in a regime where it can increase the SNR. We show analytically that such a regime exists if the qubit has a many-level structure. We also show how this physics can account for the high-fidelity avalanchelike measurement recently reported by Reed {\it et al.} [arXiv:1004.4323v1].Comment: 4 pages, 5 figure

Tunable joint measurements in the dispersive regime of cavity QED

Joint measurements of multiple qubits have been shown to open new possibilities for quantum information processing. Here, we present an approach based on homodyne detection to realize such measurements in the dispersive regime of cavity/circuit QED. By changing details of the measurement, the readout can be tuned from extracting only single-qubit to only multi-qubit properties. We obtain a reduced stochastic master equation describing this measurement and its effect on the qubits. As an example, we present results showing parity measurements of two qubits. In this situation, measurement of an initially unentangled state can yield with near unit probability a state of significant concurrence.Comment: 4 pages, 4 figure

État du développement technologique en matière d'enlèvement des métaux des effluents industriels

Cette étude trace un profil des diverses technologies utilisées et en développement pour la séparation et/ou la récupération des métaux dans les effluents industriels. Les principes de fonctionnement de ces technologies sont abordés, ainsi que leurs avantages et limites d'utilisation. Les procédés d'enlèvement et de récupération des métaux comprennent les techniques de précipitation (formation d'hydroxydes, de carbonates, de sulfures, etc.) et coprécipitation (sels de fer et d'aluminium, etc.), d'adsorption (sable, cellulose, charbon activé, pyrite, ciment, lignite, mousse de tourbe, sciure de bois, etc.) et de biosorption (bactéries, levures, moisissures, algues marines et d'eaux douces), d'électrodéposition et d'électrocoagulation, de cémentation, de séparation par membranes (osmose inverse et électrodialyse), d'extraction par solvant (acides carboxyliques, amines aliphatiques ou aromatiques, acides aminés, composés phénoliques, phosphates alkyl, etc.), et d'échange d'ions (résines naturelles et synthétiques). La précipitation ou la coprécipitation représentent les procédés les plus largement utilisés et étudiés pour l'enlèvement des métaux des effluents industriels, suivis des techniques d'adsorption. Les procédés plus sophistiqués tels que l'électrodéposition, l'extraction par solvant, la séparation par membranes et l'échange d'ions, bien que largement utilisés dans les procédés métallurgiques, sont relativement peu employés et examinés pour le traitement des effluents industriels. La biosorption a fait l'objet de plusieurs travaux de recherche au cours des dernières années et représente une option intéressante pour le traitement de divers types d'effluents contenant de faibles concentrations en métaux. Finalement, le recyclage et la gestion optimale des effluents constitue une avenue de plus en plus suivie par les industries soucieuses de satisfaire aux nouvelles réglementations et législations.This study is dedicated to the review of the different technologies used and evaluated for the removal and/or recovery of metals from industrial effluents. The principles involved in these technologies are discussed, as well as the advantages and limits associated with these processes. The metal removal and recovery processes include the following techniques: precipitation, adsorption and biosorption, electrowinning and electrocoagulation, cementation, membrane separations, solvent extraction and ion exchange.Precipitation and coprecipitation are the most used and studied methods for metal removal from industrial waste waters. The method of precipitation used most often to remove metals from waste water consists of precipitating them in the form of hydroxides. The usual procedure involves the addition of chemicals such as lime (CaO or Ca(OH)2), Mg(OH)2, NaHCO3, Na2 CO3, (NH4)2 CO3, NaOH or NH4 OH. The precipitation of metals by carbonates or sulphides is an effective alternative to hydroxide precipitation. The use of carbonates allows the precipitation of metals to occur at pH values lower than those necessary with the hydroxides. Moreover, the precipitates thus formed are denser and have better characteristics of solid-liquid separation. Precipitation by sulphides is normally carried out with reagents such as: Na2 S, NaHS, H2 S or FeS. In acidic media, the lower solubility of metal sulphides (Cd, Co, Cu, Cr, Ni, Mn, Zn, etc.), makes it possible to reach concentrations lower than those obtained by precipitation as hydroxides. Coprecipitation with aluminum and iron salts is also an effective means for the removal of metals from effluents.Adsorption methods are also widely applied and examined for this purpose. However, in most cases the use of adsorbents requires an effluent neutralization step. Indeed, the neutralization of acid effluents must take place to allow their disposal in sewerage systems. A wide variety of adsorbents can be employed, both organic and inorganic: aluminum or iron oxides, sand, activated carbon, mixtures of coal and pyrite, iron particles, gravel or crushed brick, cement, etc. Studies have demonstrated the possibility of eliminating metals by adsorption on vegetable matter: peat moss, sawdust and wood bark, etc. Chitin and chitosan, two natural polymers that are abundant in the cell walls of fungi and shellfish, also have excellent properties of metal fixation. The utilization of different agricultural by-products (peanut skins, coconuts, corn cobs, onions skins, tea leaves, coffee powder, canola meal, etc.) for metal adsorption has also been proposed.Biosorption has been intensively studied in recent years as an economical treatment for metal recovery from dilute industrial effluents. Biosorption implies the use of live or dead biomass and/or their derivatives, which adsorb the metal ions with the ligands or functional groups located on the external surface of the microbial cells. Capacities for metal adsorption on various types of biomass (bacteria, yeasts, fungi, marine and freshwater algae) have been evaluated. The microorganisms used for the metal adsorption step must usually be immobilized in a matrix or in an easily recoverable support. The immobilizing agents or matrices most usually employed are alginate, polyacrylamine, polysulphone, silica gel, cellulose and glutaraldehyde.Electrowinning is a well-established technology that is widely employed in the mining and metallurgical industries (heap leaching, acid mine drainage, etc.), in metal transformation industries (wastes from plating and metal finishing), and in the electronics and electrical industries for the removal and/or the recovery of metals in solution. Many metals (Ag, Au, Cd, Co, Cr, Cu, Ni, Pb, Sn and Zn) present in the effluents can be recovered by electrodeposition using insoluble anodes.Electrocoagulation is another electrochemical approach, which uses an electrical current to remove several metals in solution. In fact, the electrocoagulation systems can be effective in removing suspended solids, dissolved metals, tannins and dyes. The contaminants present in waste water are maintained in solution by electrical charges. When these ions and the other charged particles are neutralized with ions of opposite electric charge, provided by a electrocoagulation system, they become destabilized and precipitate in a form that is usually very stable.Cementation is a type of precipitation method implying an electrochemical mechanism. In this process, a metal having a higher oxidation potential passes into solution (e.g., oxidation of metallic iron, Fe(0), to ferrous iron, Fe(II)) to replace a metal having a lower oxidation potential. Copper is the metal most frequently separated by cementation. However, the noble metals (Ag, Au and Pd), as well as As, Cd, Ga, Pb, Sb and Sn, can also be recovered in this manner.Reverse osmosis and electrodialysis are two processes using semipermeable membranes applicable to the recovery of metal ions. In electrodialysis, selective membranes (alternation of cation and anion membranes) fit between the electrodes in electrolytic cells. A continuous electrical current and the associated ion migrations, allow the recovery of metals. The techniques of membrane separation are very efficient for the treatment of dilute waste waters.The metallurgical industry has used solvent extraction for many years for a broad range of separations. This technique is employed today for the removal of soluble metals (Cd, Cr, Co, Cu, Ni, Mo, U, V, Zn, etc.) from waste water. Separation is carried out in contact with an immiscible organic phase to form salts or complex compounds, which give a favorable solubility distribution between the aqueous and organic phases. Various types of reagents can be used for the extraction: carboxylic acids, aliphatic or aromatic amines, amino acids, alkyl phosphates, phenolic compounds. The non-selective removal of metal contaminants in aqueous solutions can be obtained with a whole range of organic reagents. Promising new reagents have been proposed recently for the selective extraction of metals, such as Cd, Co, Cr and Zn.Ion exchangers are insoluble substances having in their molecular structure acidic or basic groups able to exchange, without modification of their physical structure, the positive or negative ions fixed at these groups. The first ion exchangers used were natural substances containing aluminosilicates (zeolites, clays, etc). Nowadays, the most-used ion exchangers are mainly organic in nature (resins). For the extraction of metals, the removal of cations in solution is usually done with the sulphonic acid group (-SO3- H+) of a polystyrene resin, or, with a chelating resin containing iminodiacetate functional groups. Ion exchange has recently received considerable attention for the separation and concentration of metals from waste water. These developments are especially applicable to the plating and metal transformation industries, for the removal of Cr, Co, Cu, Cd, Ni, Fe and Zn.The more sophisticated processes, such as electrowinning, solvent extraction, membrane separations and ion exchange, although frequently used in metallurgical processes, are less popular for wastewater treatment than are precipitation methods. Finally, recycling and optimal management of effluents constitutes an approach more and more widely applied by industries to satisfy new environmental regulations and laws

Low cost silicon solar array project large area silicon sheet task: Silicon web process development

Growth configurations were developed which produced crystals having low residual stress levels. The properties of a 106 mm diameter round crucible were evaluated and it was found that this design had greatly enhanced temperature fluctuations arising from convection in the melt. Thermal modeling efforts were directed to developing finite element models of the 106 mm round crucible and an elongated susceptor/crucible configuration. Also, the thermal model for the heat loss modes from the dendritic web was examined for guidance in reducing the thermal stress in the web. An economic analysis was prepared to evaluate the silicon web process in relation to price goals

Silicon web process development

Thirty-five (35) furnace runs were carried out during this quarter, of which 25 produced a total of 120 web crystals. The two main thermal models for the dendritic growth process were completed and are being used to assist the design of the thermal geometry of the web growth apparatus. The first model, a finite element representation of the susceptor and crucible, was refined to give greater precision and resolution in the critical central region of the melt. The second thermal model, which describes the dissipation of the latent heat to generate thickness-velocity data, was completed. Dendritic web samples were fabricated into solar cells using a standard configuration and a standard process for a N(+) -P-P(+) configuration. The detailed engineering design was completed for a new dendritic web growth facility of greater width capability than previous facilities

Measurement-induced qubit state mixing in circuit QED from up-converted dephasing noise

We observe measurement-induced qubit state mixing in a transmon qubit dispersively coupled to a planar readout cavity. Our results indicate that dephasing noise at the qubit-readout detuning frequency is up-converted by readout photons to cause spurious qubit state transitions, thus limiting the nondemolition character of the readout. Furthermore, we use the qubit transition rate as a tool to extract an equivalent flux noise spectral density at f ~ 1 GHz and find agreement with values extrapolated from a $1/f^\alpha$ fit to the measured flux noise spectral density below 1 Hz.Comment: 5 pages, 4 figures. Final journal versio

Thermal Excitation of Multi-Photon Dressed States in Circuit Quantum Electrodynamics

The exceptionally strong coupling realizable between superconducting qubits and photons stored in an on-chip microwave resonator allows for the detailed study of matter-light interactions in the realm of circuit quantum electrodynamics (QED). Here we investigate the resonant interaction between a single transmon-type multilevel artificial atom and weak thermal and coherent fields. We explore up to three photon dressed states of the coupled system in a linear response heterodyne transmission measurement. The results are in good quantitative agreement with a generalized Jaynes-Cummings model. Our data indicates that the role of thermal fields in resonant cavity QED can be studied in detail using superconducting circuits.Comment: ArXiv version of manuscript to be published in the Physica Scripta topical issue on the Nobel Symposium 141: Qubits for Future Quantum Computers(2009), 13 pages, 6 figures, hi-res version at http://qudev.ethz.ch/content/science/PubsPapers.htm

Approaching Unit Visibility for Control of a Superconducting Qubit with Dispersive Readout

In a Rabi oscillation experiment with a superconducting qubit we show that a visibility in the qubit excited state population of more than 90 % can be attained. We perform a dispersive measurement of the qubit state by coupling the qubit non-resonantly to a transmission line resonator and probing the resonator transmission spectrum. The measurement process is well characterized and quantitatively understood. The qubit coherence time is determined to be larger than 500 ns in a measurement of Ramsey fringes.Comment: 4 pages, 5 figures, version with high resolution figures available at http://www.eng.yale.edu/rslab/Andreas/content/science/PubsPapers.htm