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In this thesis, I report on experiments with cold 85Rb atoms in a far-detuned one-dimensional optical lattice. These experiments are focused on creating efficient coupling between the quantized vibrational states of atoms in the optical lattice, on controlling and maintaining coherence between the vibrational states, and on developing a spectroscopy method to characterize the decay of coherence. First, I present an experimental study of the application of simple and compound pulses consisting of time-dependent spatial translations to coupling vibrational states of ultracold 85Rb atoms in the optical lattice. Experimental results show that a square pulse consisting of lattice displacements and a delay is more efficient than single-step and Gaussian pulses. The square pulse can be seen as an example of coherent control. Numerical calculations are in strong agreement with the experimental results. In addition, it is shown numerically that the vibrational state coupling due to such lattice manipulations is more efficient in shallow lattices than in deep lattices, in which the coupling probability approaches the harmonic oscillator limit. Next, the effectiveness of these pulses in reviving oscillations of atoms in vibrational superposition states using a pulse-echo technique is examined. Experimental results show that the square and Gaussian pulses result in higher echo amplitudes than the single-step pulse. These echo amplitudes are an order of magnitude larger than the echo amplitudes observed previously for the motional states of atoms in optical lattices. With the aim of the optimized square echo pulse, echo amplitude is measured at much longer times, where a surprising coherence freeze (plateau) is observed. To investigate mechanisms responsible for the observed echo decay and the coherence freeze, we developed a new two-dimensional pump-probe spectroscopy technique to monitor the evolution of frequency-frequency correlations in the system, a necessary input for understanding the decay of coherence. Through this 2D technique, we have characterized the temporal decay of frequency memory and through our simulations we find that coherence freeze is related to the shape of this memory loss function. This technique is general in that it can be applied in a variety of quantum information candidate systems to probe the nature of their decoherence.

In this thesis, I report on experiments with cold 85Rb atoms in a far-detuned one-dimensional optical lattice. These experiments are focused on creating efficient coupling between the quantized vibrational states of atoms in the optical lattice, on controlling and maintaining coherence between the vibrational states, and on developing a spectroscopy method to characterize the decay of coherence. First, I present an experimental study of the application of simple and compound pulses consisting of time-dependent spatial translations to coupling vibrational states of ultracold 85Rb atoms in the optical lattice. Experimental results show that a square pulse consisting of lattice displacements and a delay is more efficient than single-step and Gaussian pulses. The square pulse can be seen as an example of coherent control. Numerical calculations are in strong agreement with the experimental results. In addition, it is shown numerically that the vibrational state coupling due to such lattice manipulations is more efficient in shallow lattices than in deep lattices, in which the coupling probability approaches the harmonic oscillator limit. Next, the effectiveness of these pulses in reviving oscillations of atoms in vibrational superposition states using a pulse-echo technique is examined. Experimental results show that the square and Gaussian pulses result in higher echo amplitudes than the single-step pulse. These echo amplitudes are an order of magnitude larger than the echo amplitudes observed previously for the motional states of atoms in optical lattices. With the aim of the optimized square echo pulse, echo amplitude is measured at much longer times, where a surprising coherence freeze (plateau) is observed. To investigate mechanisms responsible for the observed echo decay and the coherence freeze, we developed a new two-dimensional pump-probe spectroscopy technique to monitor the evolution of frequency-frequency correlations in the system, a necessary input for understanding the decay of coherence. Through this 2D technique, we have characterized the temporal decay of frequency memory and through our simulations we find that coherence freeze is related to the shape of this memory loss function. This technique is general in that it can be applied in a variety of quantum information candidate systems to probe the nature of their decoherence.

We use normal mode decomposition to obtain phonon properties from quasi-harmonic lattice dynamics calculations and classical molecular dynamics simulations in unstrained Lennard-Jones argon superlattices with perfect and mixed interfaces. Debye scaling of phonon lifetimes at low frequencies in both perfect and mixed superlattices and Rayleigh scaling for intermediate frequencies in mixed superlattices is observed. For short period mixed superlattices, lifetimes below the Ioffe-Regel limit are observed. The relaxation-time approximation of the Boltzmann transport equation is used to predict cross-plane and in-plane thermal conductivity. We find that using a dispersion relation which includes the secondary periodicity is required to predict thermal conductivity. The assumption of perturbative disorder, where Tamura elastic mass defect scattering theory can be applied, was found to be valid for predicting cross-plane thermal conductivities but not in-plane thermal conductivities in mixed superlattices.

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We study scalar-fermion models with Yukawa interaction on a space-time lat- tice. Such models can describe the Higgs sector of the Standard Model in the case when the Higgs particle is very heavy (few hundred GeV) and there are very heavy fermions whose masses are due to their Yukawa interactions with the Higgs field. We study a realistic model with four component scalar field as well as simplified models with one and two component scalar fields. We use a mean field approximation to calculate equations for critical lines in the large d (dimension of space-time) limit. These lines are in very good agreement with available Monte Carlo data for the models at d = 4. We calculate fermion correlation functions in the mean field and large d approximations to study properties of different phases in the lattice models. We find two distinct phases with vanishing expectation values of the scalar field. One (at small Yukawa coupling Y) contains massless fermions, while in the other (at large F) the fermions have masses larger than the scale given by the inverse lattice spacing. We find that in the latter phase fermions can form bosonic bound states. These states show up as poles in a four-fermion correlator. We discuss pos- sible continuum limits in the lattice scalar-fermion models. In particular, we show that a theory defined near the critical line separating the disordered phase from the phase with antiferromagnetic order is not unitary.

Hydrogen gas production occurs in permeable reactive iron barriers (PRBs) due to the anaerobic corrosion of granular iron. Once produced, this hydrogen gas can have detrimental physical effects on PRB performance. Corrosion-produced hydrogen may accumulate in pore spaces within the PRB, thereby reducing the porosity and permeability. It may also escape the PRB system, representing a lost electron resource that may otherwise be used in reductive remediation reactions. In addition to these physical effects of hydrogen on PRB performance, chemical interactions between hydrogen and iron also occur. Hydrogen may become absorbed by the iron and stored as an electron resource within lattice imperfections. It may also interact with iron surfaces to influence the corrosion rate of the iron. These chemical interactions between hydrogen and iron may impact the reactivity of the iron granules and therefore affect PRB performance. Currently, the chemical effects of hydrogen on PRB performance remain largely unexplored. In this study, the effect of hydrogen on iron reactivity was investigated by considering hydrogen absorption into iron and hydrogen induced changes to iron corrosion rates. Hydrogen absorption by iron creates a stored electron resource within the iron granules. Release of this stored hydrogen from trapping sites represents an additional electron resource that may be used in contaminant degradation reactions. Therefore, improved hydrogen absorption may contribute to increased iron reactivity. Hydrogen absorption by granular irons has been largely unexplored in PRB performance investigations and the effect of hydrogen absorption on contaminant remediation remains unknown. In this study, an investigation of the factors governing hydrogen absorption by three granular irons, H2Omet56, H2Omet58 and H2Omet86 was conducted. The results demonstrated that rapidly corroding H2Omet86 absorbed hydrogen at a higher rate than the other more slowly corroding irons. The presence of an oxide film on H2Omet56 appeared to improve the proportion of hydrogen absorption compared to the bare irons. Ultrasonic treatment was explored as potential method of release of trapped hydrogen for improved iron reactivity. Ultrasonic treatment appeared to be unsuccessful at releasing stored hydrogen from trapping sites, but further investigations into different ultrasound conditions as well as other methods of hydrogen release could prove useful. Hydrogen gas may also influence iron reactivity by interacting with iron surfaces to alter the corrosion rate of the iron. This may occur by processes such as hydrogen enhanced anodic dissolution, hydrogen induced cracking, enhanced pitting susceptibility and reduction of iron oxides by hydrogen gas. In this study, the effect of hydrogen on iron corrosion rates was assessed by treating two iron materials (H2Omet56 and Connelly) under high pressures of hydrogen for 14 d, then comparing the post-treatment corrosion rates of hydrogen treated irons to the post-treatment corrosion rates of corresponding irons treated under low hydrogen pressures for the same period. The results demonstrated that the post-treatment corrosion rate of high hydrogen treated H2Omet56 iron was lower than the post-treatment corrosion rate of low hydrogen treated H2Omet56 iron. Hydrogen treatment did not appear to affect the post-treatment corrosion rates of Connelly iron. The effect of hydrogen on the corrosion rate of H2Omet56 iron may be a result of hydrogen enhanced anodic dissolution. The presence of a continuous oxide film on Connelly iron appeared to inhibit the effect of hydrogen enhanced anodic dissolution on Connelly iron corrosion rates. The effects of iron oxide reduction by hydrogen and hydrogen induced pitting corrosion were also considered.

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