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

The influence of stock plant fertilization on tissue concentrations of N, P and carbohydrates and the rooting of Prosopis alba cuttings.

Clonal propagation techniques are required for Prosopis due to great variability in biomass productivity, pod productivity, and nitrogen fixation from seed propagated stock. Previous studies identified a decline in the rooting percentage of cuttings taken from stock plants that were grown in the growth chamber and harvested every four weeks. To determine the influence of the mineral nutrient status of the stock plants on the rooting of cuttings, fertilized and nonfertilized Prosopis alba clone B2B50 stock plants were established under 1000 W metal halide lamps in the greenhouse. A complete macro- and micronutrient solution was used. The regrowth was harvested after 4, 8, 12, 16, and 20 weeks, and alternate nodes from each stem were taken for the rooting assay and for N, P, K. Ca, Mg, Fe, Zn an total available carbohydrate evaluation (N=79). The mean rooting percentage for the five harvest cycles was 58% for the fertilized stock plants, and 44% for the nonfertilized stock plants (P=0.087). There was no significant correlation between rooting percentage and leaf carbohydrate (P=0.964), stem carbohydrate (P=0.876) and leaf plus stem phosphorus (P=0.319). The monsignificant correlation between percent rooting and carbohydrates was negative (r=-0.018). However, there was a significant correlation with stem nitrogen and percent rooting (P=0.009) and inverse correlation between sten nitrogen and leaf carbohydrate content (r=-0.353, P=0.001). This suggests that unbalanced fertilizers, rich in nitrogen (...)

High resolution Raman spectroscopy of complexes and clusters in molecular beams

The DOE-sponsored project in this laboratory has two facets. The first is the development of methods of nonlinear Raman spectroscopy for application in studies of sparse samples. The second is the application of such methods to structural and dynamical studies of species in supersonic molecular beams. The progress we have made in both of these areas is described in this paper. The report is divided into five remaining sections. The first pertains to theoretical and experimental developments in Fourier transform stimulated emission spectroscopy and Fourier transform hole-burning spectroscopy. The second deals with progress in the development of ionization-detected stimulated Raman spectroscopies (IDSRS). The third describes results from the application of IDSRS methods to studies of jet-cooled benzene clusters. The fourth describes IDSRS results from studies of hydrogen-bonded complexes containing phenols. The fifth relates to studies of carbazole-(Ar){sub n} clusters

Analyzing intramolecular vibrational energy redistribution via the overlap intensity-level velocity correlator

Numerous experimental and theoretical studies have established that intramolecular vibrational energy redistribution (IVR) in isolated molecules has a heirarchical tier structure. The tier structure implies strong correlations between the energy level motions of a quantum system and its intensity-weighted spectrum. A measure, which explicitly accounts for this correaltion, was first introduced by one of us as a sensitive probe of phase space localization. It correlates eigenlevel velocities with the overlap intensities between the eigenstates and some localized state of interest. A semiclassical theory for the correlation is developed for systems that are classically integrable and complements earlier work focusing exclusively on the chaotic case. Application to a model two dimensional effective spectroscopic Hamiltonian shows that the correlation measure can provide information about the terms in the molecular Hamiltonian which play an important role in an energy range of interest and the character of the dynamics. Moreover, the correlation function is capable of highlighting relevant phase space structures including the local resonance features associated with a specific bright state. In addition to being ideally suited for multidimensional systems with a large density of states, the measure can also be used to gain insights into the phase space transport and localization. It is argued that the overlap intensity-level velocity correlation function provides a novel way of studying vibrational energy redistribution in isolated molecules. The correlation function is ideally suited to analyzing the parametric spectra of molecules in external fields.Comment: 16 pages, 13 figures (low resolution

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 excitation and selective intramolecular rates in supersonic molecular beams. II. Intramolecular quantum beats and IVR

An account of observations pertinent to quantum beat-modulated fluorescence decays of jet-cooled anthracene excited to S1+1380 cm^−1 is given. Based on both spectral and temporal characteristics of the beats, combined with theoretical expectations of such characteristics, it is shown that the interference phenomenon arises from the coupling of zero-order vibrational levels within the S1 manifold. (Consistent with this interpretation is the observed absence of a magnetic field effect on the beats.) As such, it is shown to be a manifestation of restricted IVR. The results of measurements of rotational band contours and the effect of carrier gas on beat parameters are used to assess the role of rotations in the coupling between vibrational levels. Specific vibration–vibration coupling schemes are briefly discussed within the context of the observations

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

Dynamics of intramolecular vibrational-energy redistribution (IVR). IV. Excess energy dependence, t-stilbene

The results of picosecond time-resolved measurements of intramolecular vibrational-energy redistribution (IVR) in jet-cooled t-stilbene are presented. The results show that the changes in the nature of IVR that were found to occur with increasing energy in anthracene also occur in t-stilbene. In particular, at intermediate energies a number of different excitations give rise to phase-shifted quantum beats in fluorescence decays, indicating restricted IVR in the molecule. At higher energies decay behavior characteristic of dissipative IVR is observed. These results are compared with those of anthracene and are discussed in terms of molecular symmetry and vibrational density of states. The results suggest the generality of the conclusions about large molecule IVR that have been stated in the other papers of this series