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

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

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

Prensado, con métodos de la cerámica plana, de piezas cerámicas curvas con especificaciones geométricas de elevada precisión

In order to obtain high-precision three-dimensional pieces by dry pressing, two approaches were studied: modelling the material flow and strain during pressing; and evaluating the bulk density (Da) distribution in a pressed piece and using shrinkage models that allow the post-firing geometry to be predicted. It would thus become possible to act in the design phase (functional geometry and rear) and in the process. This paper describes the studies carried out to predict the final geometry of three-dimensional pieces of the sheet type obtained by conventional pressing techniques, from the Da distribution in each point of the piece. For this purpose, pieces were modelled using finite element method (FEM), applying simulation processes to obtain the strain at each point of the piece as a function of its Da. The experimental validation was performed using the X-ray absorption method for Da and a CMM (coordinate measuring machine) for the geometr

Measuring quantum optical Hamiltonians

We show how recent state-reconstruction techniques can be used to determine the Hamiltonian of an optical device that evolves the quantum state of radiation. A simple experimental setup is proposed for measuring the Liouvillian of phase-insensitive devices. The feasibility of the method with current technology is demonstrated on the basis of Monte Carlo simulated experiments.Comment: Accepted for publication on Phys. Rev. Lett. 8 eps figures, 4 two-column pages in REVTE

Observable geometric phase induced by a cyclically evolving dissipative process

In a prevous paper (Phys. Rev. Lett. 96, 150403 (2006)) we have proposed a new way to generate an observable geometric phase on a quantum system by means of a completely incoherent phenomenon. The basic idea was to force the ground state of the system to evolve ciclically by "adiabatically" manipulating the environment with which it interacts. The specific scheme we have previously analyzed, consisting of a multilevel atom interacting with a broad-band squeezed vacuum bosonic bath whose squeezing parameters are smoothly changed in time along a closed loop, is here solved in a more direct way. This new solution emphasizes how the geometric phase on the ground state of the system is indeed due to a purely incoherent dynamicsComment: 6 pages, 1 figur

Tomography of Quantum Operations

Quantum operations describe any state change allowed in quantum mechanics, including the evolution of an open system or the state change due to a measurement. In this letter we present a general method based on quantum tomography for measuring experimentally the matrix elements of an arbitrary quantum operation. As input the method needs only a single entangled state. The feasibility of the technique for the electromagnetic field is shown, and the experimental setup is illustrated based on homodyne tomography of a twin-beam.Comment: Submitted to Phys. Rev. Lett. 2 eps + 1 latex figure

Reactivity of 2-acetylhydrazonemethyl-l -arylimidazole with reducing agents

La hidrogenación catalítica de los compuestos 1 origina mayoritariamente el producto resultante de la hidrogenolisis del enlace C=N y sólo se obtienen bajos rendimientos de las hidracidas 2 al utilizar Pd(C) como catalizador. La reducción con AILiH4 de la rinde, para el estereoisómero Z, la hidracida 2a; mientras que el estereoisómero E conduce por hidrogenolisis a los compuestos 4a y 5a.Catalytic hydrogenation of compounds 1 led mainly to the products resulting of the hydrogenolysis of the bond C=N, while the hydrazides 2 were obtained in small yields using Pd(C) as catalyst. Reduction of la with AILiH. yielded the hydrazide 2a for the Z stereoisomer and the products 4a and 5a for the E stereoisomer by hydrogenolysis

A Stochastic Liouville Equation Approach for the Effect of Noise in Quantum Computations

We propose a model based on a generalized effective Hamiltonian for studying the effect of noise in quantum computations. The system-environment interactions are taken into account by including stochastic fluctuating terms in the system Hamiltonian. Treating these fluctuations as Gaussian Markov processes with zero mean and delta function correlation times, we derive an exact equation of motion describing the dissipative dynamics for a system of n qubits. We then apply this model to study the effect of noise on the quantum teleportation and a generic quantum controlled-NOT (CNOT) gate. For the quantum CNOT gate, we study the effect of noise on a set of one- and two-qubit quantum gates, and show that the results can be assembled together to investigate the quality of a quantum CNOT gate operation. We compute the averaged gate fidelity and gate purity for the quantum CNOT gate, and investigate phase, bit-flip, and flip-flop errors during the CNOT gate operation. The effects of direct inter-qubit coupling and fluctuations on the control fields are also studied. We discuss the limitations and possible extensions of this model. In sum, we demonstrate a simple model that enables us to investigate the effect of noise in arbitrary quantum circuits under realistic device conditions.Comment: 36 pages, 6 figures; to be submitted to Phys. Rev.

Reactividad de 2-acetilhidrazonometil-1-arilimidazol frente a agentes reductores

Catalytic hydrogenation of compounds 1 led mainly to the products resulting of the hydrogenolysis of the bond C=N, while the hydrazides 2 were obtained in small yields using Pd(C) as catalyst. Reduction of la with AlLiH4 yielded the hydrazide 2a for the Z stereoisomer and the products 4a and 5a for the E stereoisomer by hydrogenolysis.La hidrogenación catalítica de los compuestos 1 origina mayoritariamente el producto resultante de la hidrogenolisis del enlace C=N y sólo se obtienen bajos rendimientos de las hidracidas 2 al utilizar Pd(C) como catalizador. La reducción con AlLiH4 de la rinde, para el estereoisómero Z, la hidracida 2a; mientras que el estereoisómero E conduce por hidrogenolisis a los compuestos 4a y 5a