Our concept for a quantum computational system is based on qubits encoded in vibrational normal modes of polyatomic molecules. The quantum gates are implemented by shaped femtosecond laser pulses. We adopt this concept to the new species manganese pentacarbonyl bromide [MnBr(CO)5] and show that it is a promising candidate in the mid-infrared (IR) frequency range to connect theory and experiment. As direct reference for the ab initio calculations we evaluated experimentally the absorption bands of MnBr(CO)5 in the mid-IR as well as the related transition dipole moments. The two-dimensional potential-energy surface spanned by the two strongest IR active modes and the dipole vector surfaces are calculated with density-functional theory. The vibrational eigenstates representing the qubit system are determined. Laser pulses are optimized by multitarget optimal control theory to form a set of global quantum gates: NOT, CNOT, Pi, and Hadamard. For all of them simply structured pulses with low pulse energies around 1 microJ could be obtained. Exemplarily for the CNOT gate we investigated the possible transfer to experimental shaping, based on the mask function for pulse shaping in the frequency regime as well as decomposition into a train of subpulses.

Vacancies on different sublattices in the stable and meta-stable Al 2 Cu phases Q and Q 0 have been studied by ab initio calculations. We calculate their formation energies and relaxation features. These phases exist in over-aged dilute AlCu alloys and have to grow under Al-rich conditions. Our calculations show that the preferred site for structural vacancies is on the Cu sublattice. Characteristic for early stages of aging dilute AlCu alloys are pre-Guinier-Preston (GP) zones. Here, we calculated the atomic arrangements of small clusters of Cu atoms in the aluminum matrix (Cu platelets on the {100}-planes of Al). Strong -energy lowering -relaxations of Al atoms toward the habit plane of Cu atoms possibly explain the stability of these planar configurations favored over three-dimensional agglomerations in real materials. The ab initio atomic positions for Q-and Q 0 -phases as well as for pre-GP zones have been finally used to calculate both X-ray absorption fine structure spectra and positron annihilation data -namely positron lifetimes and momentum distributions. Comparisons to the few existing experimental data are discussed and suggestions for further experiments are given.

[1] We present tools for rapid and quantitative detection of sediment lamination. The BMPix tool extracts color and gray scale curves from images at pixel resolution. The PEAK tool uses the gray scale curve and performs, for the first time, fully automated counting of laminae based on three methods. The maximum count algorithm counts every bright peak of a couplet of two laminae (annual resolution) in a smoothed curve. The zero-crossing algorithm counts every positive and negative halfway passage of the curve through a wide moving average, separating the record into bright and dark intervals (seasonal resolution). The same is true for the frequency truncation method, which uses Fourier transformation to decompose the curve into its frequency components before counting positive and negative passages. The algorithms are available at doi:10.1594/PANGAEA.729700. We applied the new methods successfully to tree rings, to well-dated and already manually counted marine varves from Saanich Inlet, and to marine laminae from the Antarctic continental margin. In combination with AMS 14 C dating, we found convincing evidence that laminations in Weddell Sea sites represent varves, deposited continuously over several millennia during the last glacial maximum. The new tools offer several advantages over previous methods. The counting procedures are based on a moving average generated from gray scale curves instead of manual counting.Copyright 2010 by the American Geophysical Union 1 of 18Hence, results are highly objective and rely on reproducible mathematical criteria. Also, the PEAK tool measures the thickness of each year or season. Since all information required is displayed graphically, interactive optimization of the counting algorithms can be achieved quickly and conveniently.

In this theoretical study vibrational ladder climbing in transition metal carbonyl complexes, as a possible means to initialize chemical ground state reactions, and the resulting vibrational population distribution using chirped mid-infrared femtosecond laser pulses is investigated. Our model system is MnBr(CO)(5), a strong IR-absorber within an experimentally easily accessible wavelength region. Special emphasis is put on the perturbation due to additional vibrational modes, especially on one, which allows dissociation at low energies. The related potential energy surface for the three representative modes is calculated, whereon quantum dynamics calculations, including the laser-molecule interaction, are performed. No significant coupling could be detected, neither in the bound, nor in the dissociative region. Contrarily, we found a dynamical barrier even for energies high above the dissociation limit. Different vibrational population distributions after the laser excitation of the CO stretching mode could be generated in dependence of the chirp parameters. Based on these findings we simulated the laser excitation corresponding to an experiment by M. Joffre et al., Proc. Natl. Acad. Ssi. U. S. A., 2004, 101(36), 13216-13220, where coherent vibrational ladder climbing in carboxyhemoglobin was demonstrated and we could offer an explanation for an open question, concerning the interpretation of the spectroscopic data.

We present dynamical transport calculations based on a tight-binding approximation to adiabatic time-dependent density functional theory (TD-DFTB). The reduced device density matrix is propagated through the Liouville-von Neumann equation. For the model system, 1,4-benzenediol coupled to aluminum leads, we are able to confirm the equality of the steady state current resulting from a time-dependent calculation to a static calculation in the conventional Landauer framework. We also investigate the response of the junction subjected to alternating bias voltages with frequencies up to the optical regime. Here we can clearly identify capacitive behaviour of the molecular device and a significant resonant enhancement of the conductance. The results are interpreted using an analytical single level model comparing the device transmission and admittance. In order to aid future calculations under alternating bias, we shortly review the use of Fourier transform techniques to obtain the full frequency response of the device from a single current trace.

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We have used positron annihilation spectroscopy to study the introduction of point defects in Zn-diffused semi-insulating GaAs. The diffusion was performed by annealing the samples for 2 h at 950 degrees C. The samples were etched in steps of 7 mu m. Both Doppler broadening using slow positron beam and lifetime spectroscopy studies were performed after each etching step. Both techniques showed the existence of vacancy-type defects in a layer of about 45 mu m. Secondary ion mass spectroscopy measurements illustrated the presence of Zn at high level in the sample almost up to the same depth. Vacancy-like defects as well as shallow positron traps were observed by lifetime measurements. We distinguish two kinds of defects: As vacancy belongs to defect complex, bound to most likely one Zn atom incorporated on Ga sublattice, and negative-ion-type positron traps. Zn acceptors explained the observation of shallow traps. The effect of Zn was evidenced by probing GaAs samples annealed under similar conditions but without Zn treatment. A defect-free bulk lifetime value is detected in this sample. Moreover, our positron annihilation spectroscopy measurements demonstrate that Zn diffusion in GaAs system is governed by kick-out mechanism

Positron lifetime measurements and Doppler-broadening spectroscopy were combined to investigate the defect properties during Cu diffusion in Te-doped GaAs. The diffusion of Cu was performed during an annealing step at 1100 • C under two different arsenic vapor pressures. The samples were quenched into room temperature water. During a subsequent isochronal annealing experiment, it was found that vacancy clusters were generated and grown, and finally they disappeared. The lifetime results show that, in addition to deep positron traps of vacancy type, positron trapping with a lifetime close to the bulk value of 228 ps occurs. The positron lifetime results give direct evidence of positron localization at shallow traps in GaAs:Te. Due to the Cu contamination during the annealing process, the shallow trap is believed to be the Cu 2− Ga double acceptor. The concentration of shallow traps is determined and found to be in good agreement with the concentration determined by Hall measurement. It decreases up to saturation with increasing annealing. The positron binding energy to these negative nonopen volume trap centers is determined to be 79 meV. It is found to be in agreement with the calculated value. Moreover, coincidence Doppler-broadening spectroscopy shows clearly that Cu atoms are bound in the direct vicinity of the observed vacancy-like defects. Theoretical calculations of momentum distribution predicted that one Cu atom incorporated into a Ga site surrounds the observed open-volume defects.