A continuous, low-velocity, nearly monochromatic atomic beam is created using laser cooling and two-dimensional magneto-optic trapping. Rubidium atoms from an effusive oven are slowed and cooled using Zeeman-tuned slowing. The scattering force from a counter-propagating, frequency-stabilized diode laser beam is used to decelerate the thermal beam of atoms to a velocity of ~ 20 m/s. A spatially varying magnetic field is used to Zeeman shift the resonance frequency of the atom to compensate for the changing Doppler shift, thereby keeping the slowing atoms resonant with the fixed frequency laser. This slowing process also cools the beam of atoms to a temperature of a few Kelvin. The slow beam of atoms is loaded into a two-dimensional magneto-optic trap or atomic funnel. The atoms are trapped along the axis of the funnel and experience a molassestype damping force in all three spatial dimensions. By frequency shifting the laser beams used to make the trap, the atoms are ejected at a controllable velocity. The continuous matter-wave source has a controllable beam velocity in the range of 2 to 15 m/s, longitudinal and transverse temperatures of approximately 500 ��K, and a flux of 3.4 x10��� atoms/s. At 10 m/s, the de Broglie wavelength of the beam is 0.5 nm. The spatial profile of the atomic beam was characterized 30 cm from the exit of the atomic funnel using a surface ionization detector. The low-velocity atomic beam is an ideal source for atom interferometry and a variety of applications in the field of atom optics. / Graduation date: 1997

Atoms in high-lying Rydberg states with large values of principal quantum number n, n ≥300, form a valuable laboratory in which to explore the control and manipulation of quantum states of mesoscopic size using carefully tailored sequences of short electric field pulses whose characteristic times (duration and/or rise/fall times) are less than the classical electron orbital period. Atoms react to such pulse sequences very differently than to short laser or microwave pulses providing the foundation for a number of new approaches to engineering atomic wavefunctions. The remarkable level of control that can be achieved is illustrated with reference to the generation of localized wavepackets in Bohr-like near-circular orbits, and the production of non-dispersive wavepackets under periodic driving and their transport to targeted regions of phase space. New protocols continue to be developed that will allow even tighter control with the promise of new insights into quantum-classical correspondence, information storage in mesoscopic systems, physics in the ultra-fast ultra-intense regime, and non-linear dynamics in driven systems.

The present work has explained a long-standing discrepency between theory and experiment: the broadening of the distances at which Rydberg atoms ionize over a metallic surface. The uneven surface potential distribution on a template-stripped gold surface evaporated on mica is measured with Kelvin probe force microscopy. The stray fields generated by the surface potential are calculated. Simulation with C++ and Matlab predicts how stray fields affect the ionization of Rydberg state atoms near a gold surface. The predicted survival probabilities for different n levels and different incident angles provided by the simulations are then compared with experiments, which shows surprisingly good agreement. Although metallic surfaces are approximately ideal equipotentials in the macroscopic world, Rydberg atoms demonstrate the important role stray fields play in the microscopic world.

Ultra-cold atoms have become an essential tool in studying unique phenomena in condensed matter systems such as superconductivity and quantum phase transitions. To accomplish these experiments we use an apparatus designed to trap and cool lithium atoms down to nano-Kelvin temperatures. Recently, significant upgrades to the laser system have been made to improve performance, increase stability, minimize maintenance and improve flexibility. We are working towards two exciting projects: proving the existence of an exotic superfluid state (FFLO) and probing the crossover between one and three-dimensions in a spin-1/2 Fermi gas with a spin-imbalance.

<p> In recent decades, research and development of organic based semiconductor devices have attracted intensive interests. One of the most essential elements is to understand the electronic structures at various interfaces involved in these devices since the interface properties control many of the critical electronic processes. It is thus necessary to study the electronic properties of the organic semiconductors with surface analytical tools to improve the understanding of the fundamental mechanisms involved in the interface formation. This thesis covers the experimental investigations on some of the most interesting topics raised in the recent development of organic electronic devices. The thesis intends to reveal the physical processes at the interface and their contribution to the device performance with photoemission and inverse photoemission investigations on the evolution of the occupied and unoccupied electronic structures. I will report a substantial difference in the electron affinity of CuPc on two substrates as the orientations of CuPc are different. I will also illustrate that the CuPc has standing up configuration on one monolayer of C60 on SiO2 while lying down on one monolayer of C60 on HOPG. Meanwhile, the CuPc on more than one monolayers of C60 on different substrates show that the substrate orientation effect vanished. Then I will propose a two-stage model to describe the bulk doping effect of C60 by molybdenum oxide. I will also demonstrate that the doping effect of C60 by ultra-thin layer molybdenum oxide is weaker than that by interface doping and bulk doping. I will demonstrate that for Au on CH3NH3PbI3, hole accumulation occurs at the vicinity of the interface, facilitating hole transfer from CH3NH3PbI3 to Au. I will show a strong initial shift of core levels to lower binding energy in C60 on CH3NH3PbI3 interface, which indicates that electrons transfer from the perovskite film to C60 molecules. I will further demonstrate that the molybdenum oxide surface can be passivated by approximately two monolayers of organic thin films against exposure to air. I will discuss the mechanism that how oxygen plasma treatment effectively recover the high work function drop of molybdenum oxide by air exposure. At the end, I will show that a small energy offset at Pentacen/C60 heterojunction makes it easy to transfer electrons from Pentacene to C60 even under a small applied bias, facilitating the occurrence of charge generation. Finally, I will summarize the thesis.</p>

Antihydrogen atoms \((\bar{H})\) are confined in a magnetic quadrupole trap for 15 to 1000 s - long enough to ensure that they reach their ground state. This milestone brings us closer to the long-term goal of precise spectroscopic comparisons of \(\bar{H}\) and H for tests of CPT and Lorentz invariance. Realizing trapped \(\bar{H}\) requires characterization and control of the number, geometry, and temperature of the antiproton \((\bar{p})\) and positron \((e^+)\) plasmas from which \(\bar{H}\) is formed. An improved apparatus and implementation of plasma measurement and control techniques make available \(10^7 \bar{p}\) and \(4 \times 10^9 e^+\) for \(\bar{H}\) experiments - an increase of over an order of magnitude. For the first time, \(\bar{p}\) are observed to be centrifugally separated from the electrons that cool them, indicating a low-temperature, high-density \(\bar{p}\) plasma. Determination of the \(\bar{p}\) temperature is achieved through measurement of the \(\bar{p}\) evaporation rate as their confining well is reduced, with corrections given by a particle-in-cell plasma simulation. New applications of electron and adiabatic cooling allow for the lossless reduction in \(\bar{p}\) temperature from thousands of Kelvin to 3.5 K or colder, the lowest ever reported. The sum of the 20 trials performed in 2011 in which \(\bar{p}\) and \(e^+\) mix to form \(\bar{H}\) in the presence of a magnetic quadrupole trap reveals a total of \(105 \pm 21\) trapped \(\bar{H}\), or \(5 \pm 1\) per trial on average. This result paves the way towards the large numbers of simultaneously trapped \(\bar{H}\) that will be necessary for laser spectroscopy. / Physics

This dissertation reports on the experimental study of coherent wavepacket dynamics of cesium atoms in the double-well potentials of a one-dimensional, far-off-resonance optical lattice. An optical lattice is the periodic potential produced by the light shift interaction of an atom with the light field of interfering laser beams. With the proper choice of laser parameters and external magnetic fields, an array of double-well potentials is created. Using the techniques of laser cooling, atoms are trapped in the lattice and are prepared in a pure state through a combination of enhanced laser cooling in a near-resonance lattice and state selection in an accelerated far-off-resonance lattice. The atoms are prepared on one side of the double-well potential, and the atomic wavepackets will then oscillate between the left and right localized states of the double-well potential. Entanglement between the internal and external degrees of freedom makes it possible to follow the center-of-mass motion of the atoms by measuring the ground state magnetic populations via Stern-Gerlach analysis. The coherent dynamics of these wavepackets was studied under various combinations of lattice parameters such as lattice depth, applied transverse and longitudinal magnetic fields. There is excellent agreement between the experimentally measured oscillation frequencies and those predicted from a numerical analysis of the bandstructure of the lattice. For certain lattice parameters the total energy of the atom is below the potential barrier and the coherent motion corresponds to tunneling through a classically forbidden barrier. At specific times during the oscillation the atomic wavepacket corresponds to a coherent superposition of the mesoscopically distinct left and right localized states.

No description available.

Abstract Not Available.

Abstract Not Available.