Control of bulk superconductivity in a BCS superconductor by surface charge doping via electrochemical gating

The electrochemical gating technique is a powerful tool to tune the surface conduction properties of various materials by means of pure charge doping, but its efficiency is thought to be hampered in materials with a good electronic screening. We show that, if applied to a metallic superconductor (NbN thin films), this approach allows observing reversible enhancements or suppressions of the bulk superconducting transition temperature, which vary with the thickness of the films. These results are interpreted in terms of proximity effect, and indicate that the effective screening length depends on the induced charge density, becoming much larger than that predicted by standard screening theory at very high electric fields

Quantum computations with atoms in optical lattices: marker qubits and molecular interactions

We develop a scheme for quantum computation with neutral atoms, based on the concept of "marker" atoms, i.e., auxiliary atoms that can be efficiently transported in state-independent periodic external traps to operate quantum gates between physically distant qubits. This allows for relaxing a number of experimental constraints for quantum computation with neutral atoms in microscopic potential, including single-atom laser addressability. We discuss the advantages of this approach in a concrete physical scenario involving molecular interactions.Comment: 15 pages, 14 figure

Site-selective laser spectroscopy of Nd 3+ ions in 0.8CaSiO 3-0.2Ca 3(PO 4) 2 biocompatible eutectic glass-ceramics

In this work we report the influence of the crystallization stage of the host matrix on the spectroscopic properties of Nd3+ ions in biocompatible glass-ceramic eutectic rods of composition 0.8CaSiO3-0.2Ca3(PO4)2 doped with 1 and 2 wt% of Nd2O3. The samples were obtained by the laser floating zone technique at different growth rates between 50 and 500 mm/h. The microstructural analysis shows that a growth rate increase or a rod diameter decrease leads the system to a structural arrangement from three (two crystalline and one amorphous) to two phases (one crystalline and one amorphous). Electron backscattering diffraction analysis shows the presence of Ca2SiO4 and apatite-like crystalline phases. Site-selective laser spectroscopy in the 4I9/2¿4F3/2/4F5/2 transitions confirms that Nd3+ ions are incorporated in crystalline and amorphous phases in these glass-ceramic samples. In particular, the presence of Ca2SiO4 crystalline phase in the samples grown at low rates, which has an excellent in vitro bioactivity, can be unambiguously identified from the excitation spectra and lifetime measurements of the 4F3/2 state of Nd3+ ions

Tailoring laser pulses with spectral and fluence constraints using optimal control theory

Within the framework of optimal control theory we develop a simple iterative scheme to determine optimal laser pulses with spectral and fluence constraints. The algorithm is applied to a one-dimensional asymmetric double well where the control target is to transfer a particle from the ground state, located in the left well, to the first excited state, located in the right well. Extremely high occupations of the first excited state are obtained for a variety of spectral and/or energetic constraints. Even for the extreme case where no resonance frequency is allowed in the pulse the algorithm achieves an occupation of almost 100%

A ‘threat’ is a ‘Threat’: Incentive effects of firing threats with varying degrees of performance information

We study the incentive effect of firing threats when bosses have limited information about workers. We show that a minimal amount of individual information about workers’ effort such as the time spent at their work station is sufficient to ensure strong incentive effects. This supports the use of firing threats based on rudimentary yet uncontroversial measures of work performance such as absenteeism, in organizational settings in which only limited information about workers is available. Our results help understand the limited link between pay and performance observed in compensation contracts calling for an extension of the principal-agent model to take into account how workers (mis-)perceive the intensity of incentives

Equation of state description of the dark energy transition between quintessence and phantom regimes

The dark energy crossing of the cosmological constant boundary (the transition between the quintessence and phantom regimes) is described in terms of the implicitly defined dark energy equation of state. The generalizations of the models explicitly constructed to exhibit the crossing provide the insight into the cancellation mechanism which makes the transition possible.Comment: 3 pages, talk given at TAUP200

On the Running of the Cosmological Constant in Quantum General Relativity

We present arguments that show what the running of the cosmological constant means when quantum general relativity is formulated following the prescription developed by Feynman.Comment: 5 page

Time-resolved fluorescence line-narrowing of Eu3+ in biocompatible eutectic glass-ceramics

The spectroscopic properties of Eu3+ in biocompatible glass and glass-ceramic eutectic rods of composition 0.8CaSiO3-0.2Ca3(PO4)2 doped with 0.5 wt% of Eu2O3 are investigated to explore their potential applications as optical probes. The samples were obtained by the laser floating zone technique. Depending on the growth rate, they exhibit three (two crystalline and one amorphous) or two (one crystalline and one amorphous) phases. The crystalline phases correspond to Ca2SiO4 and apatite-like structures. At high growth rates the system presents an amorphous arrangement which gives a glass phase. The results of time-resolved fluorescence line narrowing spectroscopy obtained under excitation within the inhomogeneous broadened 7F0¿5D0 absorption band allow to isolate the emission from Eu3+ ions in the crystalline and amorphous environments and to accurately correlate the spectroscopic properties with the microstructure of these eutectics

On the control of optical transmission of aluminosilicate glasses manufactured by the laser floating zone process

In this work, a detailed study of the properties of aluminosilicate glass rods manufactured by means of the laser floating zone (LFZ) technique is presented. Samples fabrication was carried out in controlled atmosphere using air, nitrogen, and oxygen. Transmission spectra showed that glasses manufactured in oxygen presented high optical transmission in the visible spectral range compared to those manufactured in other environments, thus allowing us to tune their optical behavior between transparent and nearly opaque through the control of the surrounding atmosphere. Microstructure and thermo- mechanical properties were also assessed, showing similar hardness, toughness, flexural strength and glass transition temperature values, and in the same range as other aluminosilicate glasses. Compositional and structural characterization in terms of energy dispersive X-ray spectroscopy (EDX) and electron paramagnetic resonance (EPR) allowed us to determine the origin of optical transmission dependence on the fabrication atmosphere