Parallel ion strings in linear multipole traps

Additional radio-frequency (rf) potentials applied to linear multipole traps create extra field nodes in the radial plane which allow one to confine single ions, or strings of ions, in totally rf field-free regions. The number of nodes depends on the order of the applied multipole potentials and their relative distance can be easily tuned by the amplitude variation of the applied voltages. Simulations using molecular dynamics show that strings of ions can be laser cooled down to the Doppler limit in all directions of space. Once cooled, organized systems can be moved with very limited heating, even if the cooling process is turned off

Structural phase transitions in multipole traps

A small number of laser-cooled ions trapped in a linear radiofrequency multipole trap forms a hollow tube structure. We have studied, by means of molecular dynamics simulations, the structural transition from a double ring to a single ring of ions. We show that the single-ring configuration has the advantage to inhibit the thermal transfer from the rf-excited radial components of the motion to the axial component, allowing to reach the Doppler limit temperature along the direction of the trap axis. Once cooled in this particular configuration, the ions experience an angular dependency of the confinement if the local adiabaticity parameter exceeds the empirical limit. Bunching of the ion structures can then be observed and an analytic expression is proposed to take into account for this behaviour

An ion ring in a linear multipole trap for optical frequency metrology

A ring crystal of ions trapped in a linear multipole trap is studied as a basis for an optical frequency standard. The equilibrium conditions and cooling possibilities are discussed through an analytical model and molecular dynamics simulations. A configuration which reduces the frequency sensitivity to the fluctuations of the number of trapped ions is proposed. The systematic shifts for the electric quadrupole transition of calcium ions are evaluated for this ring configuration. This study shows that a ring of 10 or 20 ions allows to reach a short term stability better than for a single ion without introducing limiting long term fluctuations

Ion dynamics in a linear radio-frequency trap with a single cooling laser

We analyse the possibility of cooling ions with a single laser beam, due to the coupling between the three components of their motion induced by the Coulomb interaction. For this purpose, we numerically study the dynamics of ion clouds of up to 140 particles, trapped in a linear quadrupole potential and cooled with a laser beam propagating in the radial plane. We use Molecular Dynamics simulations and model the laser cooling by a stochastic process. For each component of the motion, we systematically study the dependence of the temperature with the anisotropy of the trapping potential. Results obtained using the full radio-frequency (rf) potential are compared to those of the corresponding pseudo-potential. In the rf case, the rotation symmetry of the potential has to be broken to keep ions inside the trap. Then, as for the pseudo-potential case, we show that the efficiency of the Coulomb coupling to thermalize the components of motion depends on the geometrical configuration of the cloud. Coulomb coupling appears to be not efficient when the ions organise as a line or a pancake and the three components of motion reach the same temperature only if the cloud extends in three dimensions

Efectos de la nutrición mineral sobre la eficiencia en el uso del agua de verdeos de invierno

La nutrición mineral tiene una influencia positiva sobre la eficiencia en el uso del agua de verdeos de invierno, en relación a la producción de materia seca y la calidad de la misma. El desplazamiento de la ganadería por la agricultura hacia suelos con menor potencial estaría condicionando una menor eficiencia en el uso del agua para la producción de forraje y carne en los sistemas mixtos. Se planteó como objetivo de trabajo evaluar el efecto de la nutrición mineral (N,P) sobre la producción de forraje y eficiencia en el uso del agua en centeno establecido en un Haplustol Éntico con contenidos medios a bajos de MO y P disponible. Para llevar a cabo la experiencia se hizo un diseño de tres bloques, cada uno contó con nueve tratamientos de fertilización (N-P), utilizando parcelas de 150 m^ (10 X 15m). Se establecieron tres tratamientos de fertilización nitrogenada (N0= Okg/ha; N40= 40kg/ha y N80= 80l<gN/ha) utilizando urea granulada, aplicada "al voleo" (29/03/06) y tres tratamientos con fertilización fosforada (P0= Okg/ha; P100= 100kg/ha; P200= 200kg/ha) realizada a la siembra, con superfosfato triple de calcio como fuente de fósforo. El suelo de textura franco arenosa, con 41% de arcilla + timo, presentó contenidos de 1,7% de MO y 9 ppm de P en los primeros 20cm del perfil. La profundidad media de la tosca resultó de 80cm, dando lugar a una capacidad de retención de agua de 187mm. El uso consuntivo del verdeo resultó de 227 y 230mm de agua para los tratamientos extremos de fertilización, NO y N80 respectivamente. Se comprobó interacción significativa N-P. No existió efecto de fósforo si no hay aplicación de nitrógeno. Las dos dosis de fósforo (100 y 200) difirieron de la dosis PO cuando se aplicó N 40, mientras que cuando se aplicó N 80, todas las comparaciones entre dosis de fósforo difirieron entre si (p < 0,001). Similar comportamiento se registró con N, resultando la respuesta dependiente de la fertilización fosforada. La eficiencia en el uso del agua se incrementó significativamente desde 10,6 kg/ha.mm de materia seca para el testigo hasta 21,8 kg/ha.mm para el tratamiento de máxima fertilización. Los resultados permiten inferir la pérdida de eficiencia de la producción de forraje, en la medida que los suelos comparativamente de mayor fertilidad son asignados a la agricultura, y la necesidad de incrementar los costos por uso de fertilizantes para mantener niveles de eficiencia en la producción.Director: Dr. Alberto Quirog

Ideal Multipole Ion Traps from Planar Ring Electrodes

We present designs for multipole ion traps based on a set of planar, annular, concentric electrodes which require only rf potentials to confine ions. We illustrate the desirable properties of the traps by considering a few simple cases of confined ions. We predict that mm-scale surface traps may have trap depths as high as tens of electron volts, or micromotion amplitudes in a 2-D ion crystal as low as tens of nanometers, when parameters of a magnitude common in the field are chosen. Several example traps are studied, and the scaling of those properties with voltage, frequency, and trap scale, for small numbers of ions, is derived. In addition, ions with very high charge-to-mass ratios may be confined in the trap, and species of very different charge-to-mass ratios may be simultaneously confined. Applications of these traps include quantum information science, frequency metrology, and cold ion-atom collisions.Comment: Section on trapping of a single ion added, two figures added, one formula corrected, otherwise minor change

Physics and Applications of Laser Diode Chaos

An overview of chaos in laser diodes is provided which surveys experimental achievements in the area and explains the theory behind the phenomenon. The fundamental physics underpinning this behaviour and also the opportunities for harnessing laser diode chaos for potential applications are discussed. The availability and ease of operation of laser diodes, in a wide range of configurations, make them a convenient test-bed for exploring basic aspects of nonlinear and chaotic dynamics. It also makes them attractive for practical tasks, such as chaos-based secure communications and random number generation. Avenues for future research and development of chaotic laser diodes are also identified.Comment: Published in Nature Photonic