748 research outputs found
Strongly Enhanced Spin Squeezing via Quantum Control
We describe a new approach to spin squeezing based on a double-pass Faraday
interaction between an optical probe and an optically dense atomic sample. A
quantum eraser is used to remove residual spin-probe entanglement, thereby
realizing a single-axis twisting unitary map on the collective spin. This
interaction can be phase-matched, resulting in exponential enhancement of
squeezing. In practice the scaling and peak squeezing depends on decoherence,
technical loss, and noise. A simplified model indicates ~10 dB of squeezing
should be achievable with current laboratory parameters.Comment: 4 pages, 2 figures
Experimentally determined Si isotope fractionation between zircon and quartz
This work was supported by NSF grants EAR-1447404 and EAR-1650033, and NERC grant NE/R002134/1. PS would also like to cite the support of a Carnegie Trust Research Incentive Grant, which helped the setup of various isotope techniques in the St Andrews Isotope Geochemistry (STAiG) laboratories. FM thanks the ERC under the European Communityâs H2020 framework program/ERC grant agreement # 637503 (Pristine) and for the UnivEarthS Labex program (no. ANR-10-LABX-0023 and ANR-11-IDEX-0005-02). Parts of this work were supported by IPGP multidisciplinary program PARI, and by Region Ăźle-de-France SESAME Grant (no. 12015908).The silicon isotope composition of detrital quartz and zircon have the potential to inform us about secular changes to the silica cycle and weathering reactions on Earth. However, inferring source melt Si isotope composition from out-of-context minerals is hampered by the fact that, to-date, there is limited Si isotope equilibrium fractionation data for minerals. Here, we report experimental data to constrain Si isotope equilibrium fractionation between zircon and quartz, using two fundamentally different strategies, but with the same experimental design. First, zircon and quartz were hydrothermally synthesized from Zr(OH)4 and SiO2 at 1.5 GPa and temperatures of 725, 800, and 900 oC. The second experimental strategy utilized the three-isotope method; the starting materials consisted of natural zircon and isotopically-labelled SiO2. Three sets of hydrothermal time-series experiments were conducted at the same pressure and temperatures as the direct synthesis experiments. For all experiments, quartz and zircon were separated and 30Si/28Si and 29Si/28Si ratios were measured by solution multi-collector inductively coupled plasma mass spectrometry. The three-isotope method, which provides the best indicator of equilibrium fractionations, yields the following relationship: Î30Si(qtz-zrc) = (0.53±0.14) Ă 106 /T2 where Î30Si(qtz-zrc) is the relative difference in 30Si/28Si between quartz and zircon in permil, T is temperature in K, and the error is 2 s.e. This relationship can be used to calculate the fractionation between zircon and other phases, and to estimate the Si isotope composition of the melt from which a zircon crystallized. The results may be used to assess equilibrium-disequilibrium isotope fractionations between quartz and zircon and co-existing phases in igneous rocks. These data can also be applied to out-of-context zircon (and quartz) to estimate the isotope composition of the host rock. Zircons crystallizing from a melt derived from purely igneous sources â i.e., without the involvement of âweatheredâ material â are expected to display a ÎŽ30SiNBS-28 (permil deviation of the 30Si/28Si from the NBS-28 standard) range from -0.7 to -0.35â°. Deviations from this range indicate assimilation of non-igneous (i.e., sedimentary) material in the melt source.PostprintPeer reviewe
Accurate structure factors from pseudopotential methods
Highly accurate experimental structure factors of silicon are available in
the literature, and these provide the ideal test for any \emph{ab initio}
method for the construction of the all-electron charge density. In a recent
paper [J. R. Trail and D. M. Bird, Phys. Rev. B {\bf 60}, 7863 (1999)] a method
has been developed for obtaining an accurate all-electron charge density from a
first principles pseudopotential calculation by reconstructing the core region
of an atom of choice. Here this method is applied to bulk silicon, and
structure factors are derived and compared with experimental and Full-potential
Linear Augmented Plane Wave results (FLAPW). We also compare with the result of
assuming the core region is spherically symmetric, and with the result of
constructing a charge density from the pseudo-valence density + frozen core
electrons. Neither of these approximations provide accurate charge densities.
The aspherical reconstruction is found to be as accurate as FLAPW results, and
reproduces the residual error between the FLAPW and experimental results.Comment: 6 Pages, 3 figure
Calcareous nannofossil assemblage changes across the PaleoceneâEocene Thermal Maximum: Evidence from a shelf setting
Biotic response of calcareous nannoplankton to abrupt warming across the Paleocene/Eocene boundary reflects a primary response to climatically induced parameters including increased continental runoff of freshwater, global acidification of seawater, high sedimentation rates, and calcareous nannoplankton assemblage turnover. We identify ecophenotypic nannofossil species adapted to low pH conditions (Discoaster anartios, D. araneus, Rhomboaster spp.), excursion taxa adapted to the extremely warm climatic conditions (Bomolithus supremus and Coccolithus bownii), three species of the genus Toweius (T. serotinus, T. callosus, T. occultatus) adapted to warm, rather than cool, water conditions, opportunists adapted to high productivity conditions (Coronocyclus bramlettei, Neochiastozygus junctus), and species adapted to oligotropic and/or coolâwater conditions that went into refugium during the PETM (Zygrablithus bijugatus, Calcidiscus? parvicrucis and Chiasmolithus bidens). Discoaster anartios was adapted to meso- to eutrophic, rather than oligotrophic, conditions. Comparison of these data to previous work on sediments deposited on shelf settings suggests that local conditions such as high precipitation rates and possible increase in major storms such as hurricanes resulted in increased continental runoff and high sedimentation rates that affected assemblage response to the PETM
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Preliminary site report for the 2005 ICDP-USGS deep corehole in the Chesapeake Bay impact crater
First report for the ICDP-USGS 1.7-km-deep corehole drilled into the central part of the Chesapeake Bay impact crater during 2005
Enhanced squeezing of a collective spin via control of its qudit subsystems
Unitary control of qudits can improve the collective spin squeezing of an
atomic ensemble. Preparing the atoms in a state with large quantum fluctuations
in magnetization strengthens the entangling Faraday interaction. The resulting
increase in interatomic entanglement can be converted into metrologically
useful spin squeezing. Further control can squeeze the internal atomic spin
without compromising entanglement, providing an overall multiplicative factor
in the collective squeezing. We model the effects of optical pumping and study
the tradeoffs between enhanced entanglement and decoherence. For realistic
parameters we see improvements of ~10 dB.Comment: 5 pages, 2 figure
Density-functional embedding using a plane-wave basis
The constrained electron density method of embedding a Kohn-Sham system in a
substrate system (first described by P. Cortona, Phys. Rev. B {\bf 44}, 8454
(1991) and T.A. Wesolowski and A. Warshel, J. Phys. Chem {\bf 97}, 8050 (1993))
is applied with a plane-wave basis and both local and non-local
pseudopotentials. This method divides the electron density of the system into
substrate and embedded electron densities, the sum of which is the electron
density of the system of interest. Coupling between the substrate and embedded
systems is achieved via approximate kinetic energy functionals. Bulk aluminium
is examined as a test case for which there is a strong interaction between the
substrate and embedded systems. A number of approximations to the
kinetic-energy functional, both semi-local and non-local, are investigated. It
is found that Kohn-Sham results can be well reproduced using a non-local
kinetic energy functional, with the total energy accurate to better than 0.1 eV
per atom and good agreement between the electron densities.Comment: 11 pages, 4 figure
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