Results 1 - 10 of 31748
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[en] It is identified that barely passing electrons are the drive of the e-fishbones, rather than the barely trapped electrons at low frequency. The frequency jump in e-fishbone experiments is reproduced and analyzed. It is found that the e-fishbone frequency increases with the hot electron energy, which is consistent with the experiments. The growth rate of the mode (m = 2, n = 2) is greater than that of the mode (m = 1, n = 1). (paper)
[en] An exact controlled-NOT gate with a single trapped cold ion is usually implemented by sequentially using three laser pulses. Here, we show that two-step laser driving is sufficient to realize such a gate, as long as the initial phases and durations of the applied laser pulses and the relevant Lamb-Dicke parameter are properly set.
[en] High-energy electrons have been trapped in an intense, single-beam, ponderomotive-optical trap. Thomson-scattered light from the center of a tightly focused pulsed laser beam is enhanced when a novel trapping focus is used. The observed spatial distribution and energy dependence of the scattered light agree with the results of computer simulations for ordinary and trapping beams. (c) 1999 The American Physical Society
[en] There has been great interest in recent years in quantum control landscapes. Given an objective J that depends on a control field ε the dynamical landscape is defined by the properties of the Hessian δ2J/δε2 at the critical points δJ/δε=0. We show that contrary to recent claims in the literature the dynamical control landscape can exhibit trapping behavior due to the existence of special critical points and illustrate this finding with an example of a 3-level Λ system. This observation can have profound implications for both theoretical and experimental quantum control studies.
[en] The two dimensional eigenvalue equation describing the dissipative trapped electron mode is solved exactly in the limit of the mode overlapping many rational surfaces using the Pogutse model for the magnetic field and the pitch angle collision operator. The trapped electron contribution to the growth rate decreases, with respect to the standard theory, by a factor of order Δ/chi sub(T) << 1 where chi sub(T) is the position of the turning point and Δ the distance between rational surfaces
[en] Fermionic atoms in two different hyperfine states confined in optical lattices show strong commensurability effects due to the interplay between the atomic density wave ordering and the lattice potential. We show that spatially separated regions of commensurable and incommensurable phases can coexist. The commensurability between the harmonic trap and the lattice sites can be used to control the amplitude of the atomic density waves in the central region of the trap
[en] A broadband VLF receiver on the DE-1 satellite measures signals injected into the magnetosphere by ground-based transmitters. VLF emissions triggered by these signals indicate that the waves interact strongly with trapped energetic particles in the magnetosphere. The propagation paths from the source to the satellite are deduced on the basis of the group time delay and Doppler shift. Although there are many different paths, emissions are triggered by the later-arriving pulses that have traversed the geomagnetic equator. First satellite-based observations of emission triggering by high-power communications transmitters and their possible inplications are discussed
[en] Penning traps have been used in recent years for a variety of experiments: measurement of electronic or nuclear g factors, high precision mass measurements, or plasma studies. Three dimensional confinement of charged particles is obtained by a static electric field applied between electrodes and superposition of a magnetic field. Storage times of many hours or even days can be obtained under well defined conditions and the stored particles are then subject to investigations. We have measured the storage instabilities of electrons in a Penning trap at low magnetic fields. These measurements are carried out. as a function of the trapping voltage, for different magnetic fields. It is seen that these instabilities occur at the same positions when the trapping voltage is expressed as a percentage of the maximum voltage, given by the stability limit. The characteristic frequencies at which these instabilities occur, obey a relation that is given by ηzωz + η+ω+ + η-ω- = 0, where ωz,ω+ and ω- are the axial, perturbed cyclotron and the magnetron frequencies of the trapped electrons respectively, and the n's are integers. The reason for these instabilities are attributed to higher order static perturbations in the trapping potential. (authors)
[en] The capabilities and specific features of the formation and dynamic control of so-called contour optical traps using a fourchannel liquid crystal modulator are studied theoretically and experimentally. Circular, elliptical and C-shaped traps are formed. Trapping and confinement of absorbing micro-objects by the formed traps are demonstrated. (optical traps)