151Eu Mössbauer studies on Eu1+x Ba2−x Cu3O7+δ oxide systems

Mössbauer parameters of¹⁵¹Eu in Eu_1+x Ba_2?x Cu₃O_7+δ have been studied as a function of temperature, forx=0.15 andx=0.25. The areas of the absorption spectra for the two samples are almost equal. This could mean that thef-Mössbauer factor for¹⁵¹Eu at the barium sites is much smaller than that for¹⁵¹Eu at the rare earth sites, i.e. we only observe the spectra of the latter sites. According to this, the fits of the spectra with a single quadrupolar pattern and with two quadrupolar patterns have given equivalent χ² values.     

Quantum size effects and band structure in InSb

Quantum Size Effects (Q.S.E.) in InSb films have been detected by different experimental procedures.The work function dependence on thickness obtained from photoelectric emission threshold measurements is compared with prior results obtained with the retarding potential method. With both methods, the measured work function values are comparable. They are less than the corresponding bulk values, conforming to current theoretical predictions.The interband energy gap has been determined from photoelectric absorption band edge data: its value differs with respect to the bulk one, by the location of the first allowed energy subband in the conduction band due to the presence of Q.S.E.Some evidence is given for absence of a band structure dependence on Q.S.E.     

Superconductors in parallel field: Electromagnetic properties at the surface

Summary In the framework of the boson transformation method, a general approach to the study of finite-dimensionality superconductors is applied to the investigation of the electromagnetic properties of a semiinfinite superconductor and of a film of arbitrary thickness in the presence of a parallel external magnetic field. The magnetic-field and current density distributions near the surfaces are computed and numerical results are given for some typical cases. As an application, an estimation of the superheating field for type-II superconductor is obtained and compared with previous results.

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Riassunto Nell'àmbito del metodo della trasformazione bosonica, una tecnica generale per lo studio di superconduttori a dimensione finita è applicata allo studio delle proprietà elettromagnetiche di un superconduttore semi-infinito e di un film di spessore arbitrario. Sono calcolate le distribuzioni del campo magnetico e della densità di corrente, e sono riportati risultati numerici per qualche caso tipico. Infine, si ottiene, e si confronta con precedenti risultati, una stima del campo di surriscaldamento per superconduttori del II tipo.

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Резюме В рамках метода бозонного преобразования общий подход для исследования конечно-мерных сверхпроводников применяется к изучению электромагнитных свойств полубесконечного сверхпроводника и пленки произвольной толщины в присутствии параллельного внешнего магнитного поля. Вычисляются распределения магнитного поля и плотности тока вблизи поверхностей. Приводятся численные результаты для некоторых типичных случаев. Оценивается поле супернагревания для сверхпроводника второго рода. Оценка сравнивается с имеющимися результатами.

     

Quantum teleportation with continuous variables: A survey

Very recently, we took part in a new development of quantum information, the so-called continuous variable (CV) quantum information theory. Such a further development is mainly due to the experimental and theoretical advantages offered by CV systems, i.e., quantum systems described by a set of observables, like position and momentum, which have a continuous spectrum of eigenvalues. According to this novel trend, quantum information protocols like quantum teleportation have been suitably extended to the CV framework. Here, we briefly review some mathematical tools relative to CV systems, and we consequently develop the concepts of quantum entanglement and teleportation in the CV framework by analogy with the qubit-based approach. Some connections between teleportation fidelity and entanglement properties of the underlying quantum channel are inspected. Next, we address the study of CV quantum teleportation networks where more users share a multipartite state and an arbitrary pair of them performs quantum teleportation. In this context, we show alternative protocols, and we investigate the optimal strategy that maximizes the performance of the network.     

A solid-phase approach towards the development of 3-aza-6,8-dioxabicyclo[3.2.1]octane scaffolds

The development of new strategies for solid-phase synthesis of 3-aza-6,8-dioxabicyclo[3.2.1]octane scaffolds, named BTKa, is described. The preparation was made possible by the combination of three components: amines, alpha-halo-acetophenones, and sugar or tartaric acid derivatives. By anchoring each of the three components it was possible to synthesize BTKa compounds either as amino alcohols or amido esters. The compatibility of the protocols with different classes of amines and substituted alpha-halo-acetophenones was demonstrated.     

Mössbauer spectra of “stannite group” minerals

Stannite group minerals were studied by means of Mössbauer spectroscopy. In particular we examined the problem of stannite-kesterite miscibility. From the behaviour of the Mössbauer linewidth as a function of the mineral composition it follows that all the samples have a single phase structure, in disagreement with the existence of a miscibility gap.     

Dielectric properties of high-kappa oxides: theory and experiment for Lu2O3

We present a combined experimental and theoretical analysis of the dielectric and vibrational properties of crystalline lutetium oxide in its ground-state bixbyite structure. The vibrational dielectric function of Lu2O3 thin films grown by atomic-layer deposition was studied by infrared transmission and reflection-absorption spectroscopies, selectively accessing transverse and longitudinal optical frequencies. The static dielectric constant is extracted analyzing the infrared response. We also present first-principles density-functional linear-response calculations, which are in close agreement with experiment, and provide insight into the microscopic nature of vibrational spectra and dielectric properties.     

Stationary entanglement between macroscopic mechanical oscillators

We show that the optomechanical coupling between an optical cavity mode and two movable cavity mirrors is able to entangle two different macroscopic oscillation modes of the mirrors. This continuous variable entanglement is maintained by the light bouncing between the mirrors and is robust against thermal noise. In fact, it could be experimentally demonstrated using present technology. Received 2 September 2002 / Received in final form 10 October 2002 Published online 7 January 2003     

Vertical link solutions for multilayer optical-networks-on-chip topologies

This paper presents two different approaches that may allow the optical interconnection between superposed levels of multilayer photonic circuits as, for example, in optical-networks-on-chip. The first configuration is based on multi-mode interference devices, while the second one exploits multiple stacked directional couplers. The issues concerning the analytical and numerical design of such devices are discussed, together with a performance analysis in terms of efficiency and footprint.