Incorporation of H_2 in vitreous silica, qualitative and quantitative determination from Raman and infrared spectroscopy

Incorporation mechanisms of H_2 in silica glass were studied with Raman and infrared (IR) microspectroscopy. Hydrogenated samples were prepared at temperatures between 800 deg C and 955 deg C at 2 kbar total pressure. Hydrogen fugacities (f_{H_2}) were controlled using the double capsule technique with the iron-w\"ustite (IW) buffer assemblage generating f_{H_2} of 1290-1370 bars corresponding to H_2 partial pressures (P_{H_2}) of 960-975 bars. We found that silica glass hydrogenated under such conditions contains molecular hydrogen (H_2) in addition to SiH and SiOH groups. H_2 molecules dissolved in the quenched glasses introduce a band at 4136 cm^{-1} in the Raman spectra which in comparison to that of gaseous H_2 is wider and is shifted to lower frequency. IR spectra of hydrogenated samples contain a band at 4138 cm^{-1} which we assign to the stretching vibration of H_2 molecules located in non-centrosymmetric sites. The Raman and IR spectra indicate that the dissolved H_2 molecules interact with the silicate network. We suggest that the H_2 band is the envelope of at least three components due to the occupation of at least three different interstitial sites by H_2 molecules. Both, Raman and IR spectra of hydrogenated glasses contain bands at ~2255 cm^{-1} which may be due to the vibration of SiH groups

Quantum Information Encoding, Protection, and Correction from Trace-Norm Isometries

We introduce the notion of trace-norm isometric encoding and explore its implications for passive and active methods to protect quantum information against errors. Beside providing an operational foundations to the "subsystems principle" [E. Knill, Phys. Rev. A 74, 042301 (2006)] for faithfully realizing quantum information in physical systems, our approach allows additional explicit connections between noiseless, protectable, and correctable quantum codes to be identified. Robustness properties of isometric encodings against imperfect initialization and/or deviations from the intended error models are also analyzed.Comment: 10 pages, 1 figur

Causal structure of the entanglement renormalization ansatz

We show that the multiscale entanglement renormalization ansatz (MERA) can be reformulated in terms of a causality constraint on discrete quantum dynamics. This causal structure is that of de Sitter space with a flat spacelike boundary, where the volume of a spacetime region corresponds to the number of variational parameters it contains. This result clarifies the nature of the ansatz, and suggests a generalization to quantum field theory. It also constitutes an independent justification of the connection between MERA and hyperbolic geometry which was proposed as a concrete implementation of the AdS-CFT correspondence

Geochemical Study of Natural CO2 Emissions in the French Massif Central: How to Predict Origin, Processes and Evolution of CO2 Leakage

International audienceThis study presents an overview of some results obtained within the French ANR (National Agency of Research) supported Géocarbone-Monitoring research program. The measurements were performed in Sainte-Marguerite, located in the French Massif Central. This site represents a natural laboratory for CO2/fluid/rock interactions studies, as well as CO2 migration mechanisms towards the surface. The CO2 leaking character of the studied area also allows to test and validate measurements methods and verifications for the future CO2 geological storage sites. During these surveys, we analyzed soil CO2 fluxes and concentrations. We sampled and analyzed soil gases, and gas from carbo-gaseous bubbling springs. A one-month continuous monitoring was also tested, to record the concentration of CO2 both in atmosphere and in the soil at a single point. We also developed a new methodology to collect soil gas samples for noble gas abundances and isotopic analyses, as well as carbon isotopic ratios. Our geochemical results, combined with structural geology, show that the leaking CO2 has a very deep origin, partially mantle derived. The gas rises rapidly along normal and strike-slip active faults. CO2 soil concentrations (also showing a mantle derived component) and CO2 fluxes are spatially variable, and reach high values. The recorded atmospheric CO2 is not very high, despite the important CO2 degassing throughout the whole area

Approximate simulation of quantum channels

10.1103/PhysRevA.84.022333Physical Review A - Atomic, Molecular, and Optical Physics842-PLRA