37 research outputs found
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