666 research outputs found
Motion Tomography of a single trapped ion
A method for the experimental reconstruction of the quantum state of motion
for a single trapped ion is proposed. It is based on the measurement of the
ground state population of the trap after a sudden change of the trapping
potential. In particular, we show how the Q function and the quadrature
distribution can be measured directly. In an example we demonstrate the
principle and analyze the sensibility of the reconstruction process to
experimental uncertainties as well as to finite grid limitations. Our method is
not restricted to the Lamb-Dicke Limit and works in one or more dimensions.Comment: 4 pages, Revtex format, 4 postscript figures, changed typographical
error
Quantum gates with "hot" trapped ions
We propose a scheme to perform a fundamental two-qubit gate between two
trapped ions using ideas from atom interferometry. As opposed to the scheme
considered by J. I. Cirac and P. Zoller, Phys. Rev. Lett. 74, 4091 (1995), it
does not require laser cooling to the motional ground state.Comment: 4 pages, 2 eps figure
Reconstruction of Liouvillian Superoperators
We show how to determine (reconstruct) a master equation governing the time
evolution of an open quantum system.
We present a general algorithm for the reconstruction of the corresponding
Liouvillian superoperators. Dynamics of a two-level atom in various
environments is discussed in detail.Comment: 4 pages, revtex, 1 eps figure, accepted for publication in Phys. Rev.
Complete Characterization of a Quantum Process: the Two-Bit Quantum Gate
We show how to fully characterize a quantum process in an open quantum
system. We particularize the procedure to the case of a universal two-qubit
gate in a quantum computer. We illustrate the method with a numerical
simulation of a quantum gate in the ion trap quantum computer.Comment: Accepted for publication in Physical Review Letters 08Nov96
(submitted 15Jly96
Seasonal controls on net branch CO2 assimilation in sub-Arctic Mountain Birch (Betula pubescens ssp. czerepanovii (Orlova) Hamet-Ahti)
Forests at northern high latitudes are experiencing climate-induced changes in growth and productivity, but our knowledge on the underlying mechanisms driving seasonal CO2 fluxes in northern boreal trees comes almost exclusively from ecosystem-level studies on evergreen conifers. In this study, we measured growing season whole-branch CO2 exchange in a deciduous tree species of the tundra-taiga ecotone, Mountain Birch (Betula pubescens ssp. czerepanovii (Orlova) Hamet-Ahti), at two locations in northern Fennoscandia: Abisko (Sweden) and Kevo (Finland). We identified strong seasonal and environmental controls on both photosynthesis and respiration by analysing the parameters of light response curves. Branch-level photosynthetic parameters showed a delayed response to temperature, and, at Kevo, they were well described by sigmoid functions of the state of acclimation (S). Temperature acclimation was slower (time constant, τ = 7 days) for maximum photosynthesis (βbr) than for quantum efficiency (αbr) (τ = 5 days). High temperature-independent values of the respiration parameter (γbr) during leaf and shoot expansion were consistent with associated higher growth respiration rates. The ratio γbr/βbr was positively related to temperature, a result consistent with substrate-induced variations in leaf respiration rates at the branch level. Differences in stand structure and within-site variation in the active period of C uptake determined the spatiotemporal patterns in net assimilation amongst branches. Growing season CO2 uptake of individual branches on a leaf area basis did not show a significant relationship with total incident photosynthetically active radiation, and did not differ across sites, averaging ca. 640 g CO2 m−2
A quantum phase gate implementation for trapped ions in thermal motion
We propose a novel scheme to implement a quantum controlled phase gate for
trapped ions in thermal motion with one standing wave laser pulse. Instead of
applying the rotating wave approximation this scheme makes use of the
counter-rotating terms of operators. We also demonstrate that the same scheme
can be used to generate maximally entangled states of trapped ions by a
single laser pulse
Distinguishing n Hamiltonians on C^n by a single measurement
If an experimentalist wants to decide which one of n possible Hamiltonians
acting on an n dimensional Hilbert space is present, he can conjugate the time
evolution by an appropriate sequence of known unitary transformations in such a
way that the different Hamiltonians result in mutual orthogonal final states.
We present a general scheme providing such a sequence.Comment: 4 pages, Revte
Avulsión del tubérculo tibial asociada a epifisiólisis proximal de tibia
Las lesiones de la tuberosidad tibial anterior son fracturas poco frecuentes que se
presentan generalmente en adolescentes. Su extensión fisaria hacia la cortical posterior constituye
un hecho infrecuente. Algunos autores consideran necesaria la modificación de la clasifícacion
de Watson-Jones añadiéndole un tipo IV. Se presenta un caso de epifisiólisis proximal de tibia asociada
a avulsión del tubérculo tibial, se discute dicha clasificación, el mecanismo de producción
y revisión de la literaturaFractures of the anterior tibial tubercle are uncommon lesions, adolescents being
more frequently affected. Physeal extension through the posterior tibial cortical bone is rare. Some
authors have suggested that a new type IV can be added to the Watson-Jones classiflcation. In
this paper, we report a case with epiphysiolisis of the proximal tibia associated to an avulsion fracture
of the anterior tibial tubercle. The Watson-Jones classiflcation, the mechanism of injury are
discussed together a review of the literature
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