Optimal laser-control of double quantum dots

Coherent single-electron control in a realistic semiconductor double quantum dot is studied theoretically. Using optimal-control theory we show that the energy spectrum of a two-dimensional double quantum dot has a fully controllable transition line. We find that optimized picosecond laser pulses generate population transfer at significantly higher fidelities (>0.99) than conventional sinusoidal pulses. Finally we design a robust and fast charge switch driven by optimal pulses that are within reach of terahertz laser technology.Comment: 5 pages, 4 figure

Can optical spectroscopy directly elucidate the ground state of C20?

The optical response of the lowest energy members of the C20 family is calculated using time-dependent density functional theory within a real-space, real-time scheme. Significant differences are found among the spectra of the different isomers, and thus we propose optical spectroscopy as a tool for experimental investigation of the structure of these important clusters.Comment: 11 pages, 2 figures. To be published in J. Chem. Phy

Tailored pump-probe transient spectroscopy with time-dependent density-functional theory: controlling absorption spectra

Recent advances in laser technology allow us to follow electronic motion at its natural time-scale with ultra-fast time resolution, leading the way towards attosecond physics experiments of extreme precision. In this work, we assess the use of tailored pumps in order to enhance (or reduce) some given features of the probe absorption (for example, absorption in the visible range of otherwise transparent samples). This type of manipulation of the system response could be helpful for its full characterization, since it would allow us to visualize transitions that are dark when using unshaped pulses. In order to investigate these possibilities, we perform first a theoretical analysis of the non-equilibrium response function in this context, aided by one simple numerical model of the hydrogen atom. Then, we proceed to investigate the feasibility of using time-dependent density-functional theory as a means to implement, theoretically, this absorption-optimization idea, for more complex atoms or molecules. We conclude that the proposed idea could in principle be brought to the laboratory: tailored pump pulses can excite systems into light-absorbing states. However, we also highlight the severe numerical and theoretical difficulties posed by the problem: large-scale non-equilibrium quantum dynamics are cumbersome, even with TDDFT, and the shortcomings of state-of-the-art TDDFT functionals may still be serious for these out-of-equilibrium situations

A Hemispherical Contact Model for Simplifying 3D Occlusal Surfaces

Statement of problem Currently, dental articulators can recreate mandibular movements and occlusal contacts. However, whether virtual articulators can also provide information about occluding dental surfaces, functional movements, and the mandibular condyles is unclear. Purpose The purpose of this in vitro study was to evaluate the occluding surfaces on dental casts obtained from a patient and approximate them to a hemispherical contact model. Both models were tested by digitizing the Dentatus ARL dental articulator. Material and methods A combination of photogrammetry and structure from motion methods were used to scan a Dentatus ARL articulator and representative dental casts. Using computer-aided engineering and finite element analysis, contact points and action vectors to the forces on occluding surfaces and condyles were obtained for cast and hemispherical models. This experiment was performed using centric occlusion and 3 different condylar inclinations. The Kruskal-Wallis 1-way analysis of variance on ranks test was used to allow all pairwise comparisons between condylar inclination and mechanical action vector values in each location (α=.05). Results Action vectors from the cast model and each location of the hemispherical model were calculated to show the mechanical consequences and the similarity among models. Overall, no significant differences were observed for action vectors (A20 versus A40 versus A60) at each location (dental cast/hemisphere, right condylar, and left condylar) in the analysis of dental casts and the hemisphere model (.382≤P≤.999). Conclusions This study provided graphical information that may assist the dental professional in determining which occlusal contacts should be modified to attain condylar and balanced centric occlusion

Floquet engineering the band structure of materials with optimal control theory

We demonstrate that the electronic structure of a material can be deformed into Floquet pseudobands with arbitrarily tailored shapes. We achieve this goal with a combination of quantum optimal control theory and Floquet engineering. The power and versatility of this framework is demonstrated here by utilizing the independent-electron tight-binding description of the π electronic system of graphene. We show several prototype examples focusing on the region around the K (Dirac) point of the Brillouin zone: creation of a gap with opposing flat valence and conduction bands, creation of a gap with opposing concave symmetric valence and conduction bands (which would correspond to a material with an effective negative electron-hole mass), and closure of the gap when departing from a modified graphene model with a nonzero field-free gap. We employ time-periodic drives with several frequency components and polarizations, in contrast to the usual monochromatic fields, and use control theory to find the amplitudes of each component that optimize the shape of the bands as desired. In addition, we use quantum control methods to find realistic switch-on pulses that bring the material into the predefined stationary Floquet band structure, i.e., into a state in which the desired Floquet modes of the target bands are fully occupied, so that they should remain stroboscopically stationary, with long lifetimes, when the weak periodic drives are started. Finally, we note that although we have focused on solid state materials, the technique that we propose could be equally used for the Floquet engineering of ultracold atoms in optical lattices and for other nonequilibrium dynamical and correlated systems

Hß photometry for uvby standard stars

From 1984 to 1986, we made several observational campaigns at Calar Alto and La Palma Observator­ies using the uvby and ß photometric systems to monitor a selected sample of late-type variable stars. In this paper we present the ß values for 38 uvby standard stars to contribute to the uvby-ß calibration works on late-type stars. In the final discussion, the ß computed values are plotted against the Ström­gren b - y, m_1, and c_1 indices