Laser phase modulation approaches towards ensemble quantum computing

Selective control of decoherence is demonstrated for a multilevel system by generalizing the instantaneous phase of any chirped pulse as individual terms of a Taylor series expansion. In the case of a simple two-level system, all odd terms in the series lead to population inversion while the even terms lead to self-induced transparency. These results also hold for multiphoton transitions that do not have any lower-order photon resonance or any intermediate virtual state dynamics within the laser pulse-width. Such results form the basis of a robustly implementable CNOT gate.Comment: 10 pages, 4 figures, PRL (accepted

Picosecond excitation of jet-cooled hydrogen-bonded systems: Dispersed fluorescence and time-resolved studies of methyl salicylatea

Long progressions involving frequency intervals of 180 cm^(−1) are observed in the fluoresence of MS for 3327.5 Å excitation. (AIP

Observation of intracavity absorption of molecules in supersonic beams

Intracavity absorption studies of DMT and I2 are reported at rotational and vibrational temperatures of <0.1 K and 16 K, respectively

Spanwise loading distribution and wake velocity surveys of a semi-span wing

The spanwise distribution of bound circulation on a semi-span wing and the flow velocities in its wake were measured in a wind tunnel. Particular attention was given to documenting the flow velocities in and around the development tip vortex. A two-component laser velocimeter was used to make the velocity measurements. The spanwise distribution of bound circulation, three components of the time-averaged velocities throughout the near wake their standard deviations, and the integrated forces and moments on a metric tip as measured by an internal strain gage balance are presented without discussion

Performance and loads data from a hover test of a 0.658-scale V-22 rotor and wing

A hover test of a 0.658-scale model of a V-22 rotor and wing was conducted at the Outdoor Aerodynamic Research Facility at Ames Research Center. The primary objectives of the test were to obtain accurate measurements of the hover performance of the rotor system, and to measure the aerodynamic interactions between the rotor and wing. Data were acquired for rotor tip Mach numbers ranging from 0.1 to 0.73. This report presents data on rotor performance, rotor-wake downwash velocities, rotor system loads, wing forces and moments, and wing surface pressures

Picosecond dynamics and photoisomerization of stilbene in supersonic beams. I. Spectra and mode assignments

In this and the following paper, we present a full account of our earlier report [Syage et al., Chem. Phys. Lett. 88, 268 (1982)] on the spectra and picosecond dynamics of stilbene isomerization in supersonic jets. The jet-cooled excitation and dispersed fluorescence spectra of t-stilbene-h12 and -d12 are reported and assigned for the Bu 00 wavelengths for h12 and d12 (in excitation) are 3101.4 and 3092.5 Å, respectively. Previously unidentified low frequency modes (as low as 20 cm^−1 in S0 for -h12) have been observed and tentatively assigned as out-of-plane modes of au symmetry in C2h. This indicates that t-stilbene has a propeller-like geometry involving phenyl rotation (i.e., C2 symmetry). A Franck–Condon analysis of the low frequency modes and particularly the ag, nu25 in-plane symmetric bend mode indicates that a large geometry change takes place upon electronic excitation possibly due to a delocalization of double bond character from the Ce–Ce bond to Ce–[cursive phi] bond. The geometry change of the in-plane Ce–Ce–[cursive phi] between S1 and S0 was determined from the Franck–Condon and a normal mode analysis to be 1.3°±0.3°. The rms amplitude of this bend motion for the symmetric nu25 bend mode (for one quanta in S0) is |^2|^1/2=1.0±0.2°. Most ag modes involving benzene-type vibrations (other than C–H stretch modes) have been assigned. Dispersed fluorescence spectra exhibited a broad background indicative of IVR which increased rapidly with S1 vibrational energy. The spectra were completely diffuse above 1200 cm^−1 which is consistent with the barrier for isomerization being at about 1100–1200 cm^−1. The excitation spectra show a rapid decline in intensity at higher energies due to the process of isomerization which competes with radiative decay. However, sharp (albeit weak) structure could still be discerned at energies well in excess of 2000 cm^−1. In the accompanying paper, we present results on the dynamics of isomerization and its dependence on mode mixing and the nature of the reactive surface (adiabatic vs diabatic)

Picosecond dynamics and photoisomerization of stilbene in supersonic beams. II. Reaction rates and potential energy surface

Using picosecond excitation in a supersonic jet, we present a full account of our earlier report on the dynamics of state-selective photoisomerization of t-stilbene. Collisionless isomerization in this case indicates the twisting of the molecule about the ethylene bond away from the trans configuration Central to this reaction is the question of vibrational energy redistribution or IVR. From direct (single vibronic level) time-resolved measurements, relative fluorescence quantum yields from relaxed and unrelaxed states, and a thorough vibrational analysis from excitation and dispersed fluorescence spectra (previous paper), the following conclusions are reached: (i) The IVR yield is state selective being more extensive from combination modes than from fundamental modes of similar energy. The IVR yield becomes very significant above [approximately-equal-to]900–1000 cm^−1. The rate is much faster than the reaction at all energies studies. (ii) The barrier to isomerization is observed at 3.3±0.2 kcal/mol (1100–1200 cm^−1). The radiative lifetimes, measured from the 0° level fluorescence decays, are 2.7±0.1 ns (h12) and 2.5±0.1 ns (d12). (iii) The observed isomerization rates in the isolated molecule are approximately an order of magnitude less than the calculated RRKM rates and observed solution phase rates. (iv) The apparent non-RRKM behavior in the isolated behavior is explained by considering the nature of IVR and by adopting a diabatic representation of the reactive surface (i.e., an allowed surface) using a Landau–Zener–Stueckelberg model. (v) Finally, we compare t-stilbene with other related isolated molecules and to solution phase t-stilbene results in order to assess the role of mode mixing and the nature of the reactive surface

Picosecond excitation and selective intramolecular rates in supersonic molecular beams. III. Photochemistry and rates of a charge transfer reaction

The picosecond state-selective dynamics and photochemistry of the molecule A–(CH2)3–[cursive phi], where A and [cursive phi] are aromatic chromophores, was studied under collision-free conditions in a supersonic beam. Time-resolved fluorescence measurements of the reactant and the charge transfer (exciplex) product were undertaken as a function of specific vibrational energy above the zero point level of S1. From these studies along with an analysis of the excitation spectra, dispersed flourescence, and quantum yields, the following results and conclusions were reached: (i) IVR is much faster than reaction at all excess energies studied. (ii) The energy threshold for product formation is E0[approximately-equal-to]900 cm^−1 (2.6 kcal/mol). The analysis of the rates using an effective temperature model gives a frequency factor of A0[approximately-equal-to]1.2×10^10 s^−1. Four torsions were identified as critical to the reaction dynamics which were modeled according to a multidimensional reaction coordinate using an RRKM scheme. (iii) The thermodynamics of the isolated charge transfer product indicates strong stabilization DeltaH=−9.2 kcal/mol and extensive charge transfer, the static dipole moment is 13 D, and the charge transfer contribution to the total electronic wave function |c2|^2 is 0.86. (iv) A comparison of the present work to solution phase studies of A–(CH2)3–[cursive phi] indicates similar static properties but different dynamics. The calculated thermal (room temperature) reaction time for exciplex formation in the vapor (540 ps) was compared to the shortest observed value in solution (1.4 ns) to assess the role of the solvent on the chain motions which lead to product formation

Localization of Two-dimensional Electron Gas in LaAlO3/SrTiO3 Heterostructures

We report strong localization of 2D electron gas in LaAlO3 / SrTiO3 epitaxial thin-film heterostructures grown on (LaAlO3)0.3-(Sr2AlTaO3)0.7 substrates by using pulsed laser deposition with in-situ reflection high-energy electron diffraction. Using longitudinal and transverse magnetotransport measurements, we have determined that disorder at the interface influences the conduction behavior, and that increasing the carrier concentration by growing at lower oxygen partial pressure changes the conduction from strongly localized at low carrier concentration to metallic at higher carrier concentration, with indications of weak localization. We interpret this behavior in terms of a changing occupation of Ti 3d bands near the interface, each with a different spatial extent and susceptibility to localization by disorder, and differences in carrier confinement due to misfit strain and point defects.Comment: 12 pages, 4 figure