<p> Presented in this thesis is the construction of an apparatus to produce optically trapped ⁶Li atoms in the two lowest hyperfine states, the observation of cooling the trapped atoms by parametric excitation, and a study on the searching for itinerant ferromagnetism in a two-dimensional Fermi gas.</p> <p> </p> <p> In the parametric cooling experiment, a technique is developed to cool a cold atomic Fermi gas by parametrically driving atomic motions in a crossed-beam optical dipole trap. This method employs the anharmonicity of the optical dipole trap, in which the hotter atoms at the edge of the trap feel the anharmonic components of the trapping potential, while the colder atoms in the center of the trap feel the harmonic one. By modulating the trap depth with frequencies that are resonant with the anharmonic components, hotter atoms are selectively excited out of the trap while keeping the</p> <p> colder atoms in the trap, generating a cooling effect.</p> <p> </p> <p> An analytical study of itinerant ferromagnetism in a two-dimensional atomic Fermi gas is presented, based on the past experiments done with three-dimensional Fermi gases. Here, the formation of repulsive polarons in a strongly-interacting Fermi gas is used as an initial condition.Then the observation of itinerant ferromagnetism is realized by detection of ferromagnetic domains in the two-dimensional gas.</p> <p> </p> <p> Additionally, an experiment and simulation is performed on the effect of velocity-changing collisions on the absolute absorption of ⁶Li vapor in an Ar buffer gas. The dependence of probe beam absorption is observed by variation of beam intensity and spatial evolution. The simulation of an effective three-level energy model with velocity-changing collisions determines a collision rate that agrees with transmission data collected.</p>

No description available.

No description available.

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

<p>When $N$ non-interacting atoms interact with a single frequency laser with no phase difference between the photons interacting with the atoms, their interaction can be described collectively \cite{dicke}. For instance, suppose that there is a two level atom with state $|\Psi_1\rangle=\alpha_1|a\rangle+\beta_1|b\rangle$, and another two level atom with state $|\Psi_2\rangle=\alpha_2|a\rangle+\beta_2|b\rangle$. We assume that the two internal states $|a\rangle$ and $|b\rangle$ are indistinguishable between the atoms. Since they are non-interacting atoms, the total state of the system with the two atoms is $|\Psi\rangle_C=\alpha_1\alpha_2|aa\rangle+\alpha_1\beta_2|ab\rangle+\beta_1\alpha_2|ba\rangle+\beta_1\beta_2|bb\rangle$. By rotating the states $|ab\rangle$ and $|ba\rangle$, we can redefine the system using two new basis states, $|+\rangle=(|ab\rangle+|ba\rangle)/\sqrt{2}$ and $|-\rangle=(|ab\rangle-|ba\rangle)/\sqrt{2}$. The state of the system with these states is $|\Psi\rangle_C=\alpha_1\alpha_2|aa\rangle+(\alpha_1\beta_2+\beta_1\alpha_2)/\sqrt{2}|+\rangle+(\alpha_1\beta_2-\beta_1\alpha_2)/\sqrt{2}|-\rangle+\beta_1\beta_2|bb\rangle$. If the two atoms interact with the same field, they evolve in the same way, so that $\alpha_1=\alpha_2\equiv\alpha$ and $\beta_1=\beta_2\equiv\beta$. Hence, the $|-\rangle$ state, which is the antisymmetric state, vanishes, and only the symmetric states remain in the system, so that the total state of the system can be described by $|\Psi\rangle_C=\alpha</p><p>2|aa\rangle+\sqrt{2}\alpha\beta|+\rangle+\beta</p><p>2|bb\rangle$. The remaining states are what are known as the symmetric Dicke states, symmetric collective states, or collective spin states. This two atom case can be generalized to $N$ atoms; for $N$ atoms, there are $N+1$ symmetric collective states. They have been studied since Dicke's seminal paper in the 1950s , especially with respect to superradiance \cite{bonifacio,rehler,skribanowitz,gross,kaluzny,l ambert} and squeezed states \cite{kitagawa,kuzmich01,hald,sorenson}. We first studied the symmetric collective states for the purpose of quantum computing. Using Rydberg atoms, we showed that with the proper choice of experimental parameters, the excitation of the collective states can be confined to just the ground state and the first excited state by way of differential light shifts. We called this the Rydberg assisted light shift imbalance induced blockade. Such a two level system is important in quantum computing because it can be used as a qubit, a building block of quantum computers. Although the collective state description of Rydberg atoms is quite complicated, since it requires more than just the two traditional hyperfine ground states of an alkali atom, we were able to successfully simplify the system and find the conditions necessary for the proper light shifts to occur to our advantage. The simulations supported our results and we published the results \cite{tu}. We then moved on to study whether the collective states could be used to make atomic clocks and interferometers. In the case of a collective state atomic clock (COSAC), we found that the Ramsey fringes narrowed by a factor of $\sqrt{N}$ compared to a conventional clock -- $N$ being the number of non-interacting atoms -- without violating the uncertainty relation. This narrowing is explained as being due to interferences among the collective states, representing an effective $\sqrt{N}$ fold increase in the clock frequency, without entanglement. We discuss the experimental inhomogeneities that affect the signal and show that experimental parameters can be adjusted to produce a near ideal signal. The detection process collects fluorescence through stimulated Raman scattering of Stokes photons, which emits photons predominantly in the direction of the probe beam for a high enough optical density. By using a null measurement scheme, in which detection of zero photons corresponds to the system being in a single collective state, we detect the population in a collective state of interest. The quantum and classical noise of the ideal COSAC is still limited by the standard quantum limit and performs only as well as the conventional clock. However, when detection efficiency and collection efficiency are taken into account, the detection scheme of the COSAC increases the quantum efficiency of detection significantly in comparison to a typical conventional clock employing fluorescence detection, yielding a net improvement in stability by as much as a factor of 10. For the off-resonant Raman excitation based COSAC, the theory and results from simulations were published together \cite{kim}; the experiment is underway, and we hope to publish the results in a few months. The COSAC can also be described in terms of the coherent population transfer (CPT) states. The theory behind it is being polished and will be published soon. The collective state atomic interferometer is also possible, with similar inhomogeneities being present in such system, as well \cite{shahriar03}. This dissertation is organized as follows: In Chapter \ref{chap1}, the fundamental atomic interactions with the electric field and magnetic field are used to derive the interaction Hamiltonian and the density matrix formulation. Chapter \ref{chap3} comprises of the theoretical work and simulation results regarding Rydberg assisted light shift imbalance induced blockade. This chapter introduces collective states. For a more thorough investigation into these states, recommended reading includes Dicke's seminal paper \cite{dicke}, and other references \cite{sargent,mandel}. Chapter \ref{chap4} discusses the off-resonant Raman-Rabi excitation based COSAC, and Chapter \ref{chap5} follows it up with the discussion on coherent population trapping based COSAC. In Chapter \ref{chap6}, I discuss the ongoing experimental progress and the preliminary results we have obtained thus far. I conclude in Chapter \ref{chap7} with future work. Finally, some of the key programs used for simulations are included in the appendices. In Appendix \ref{a1}, some of the MATLAB programs used in the evolution of the density matrix, and the steady state solution of the master equation, in Chapter \ref{chap3} are included. In Appendix \ref{a2}, the more sophisticated Python programs used for Chapter \ref{chap4} are included. Despite the rumors I have heard about no one actually reading anyone else's dissertations, I hope that someone will find the information in here useful in the future.

Indiana University-Purdue University Indianapolis (IUPUI) / Presented in this thesis is the construction of an apparatus to produce optically trapped lithium-6 atoms in the two lowest hyperfine states, the observation of cooling the trapped atoms by parametric excitation, and a study on the searching for itinerant ferromagnetism in a two-dimensional Fermi gas. In the parametric cooling experiment, a technique is developed to cool a cold atomic Fermi gas by parametrically driving atomic motions in a crossed-beam optical dipole trap. This method employs the anharmonicity of the optical dipole trap, in which the hotter atoms at the edge of the trap feel the anharmonic components of the trapping potential, while the colder atoms in the center of the trap feel the harmonic one. By modulating the trap depth with frequencies that are resonant with the anharmonic components, hotter atoms are selectively excited out of the trap while keeping the colder atoms in the trap, generating a cooling effect. An analytical study of itinerant ferromagnetism in a two-dimensional atomic Fermi gas is presented, based on the past experiments done with three-dimensional Fermi gases. Here, the formation of repulsive polarons in a strongly-interacting Fermi gas is used as an initial condition. Then the observation of itinerant ferromagnetism is realized by detection of ferromagnetic domains in the two-dimensional gas. Additionally, an experiment and simulation is performed on the effect of velocity-changing collisions on the absolute absorption of lithium-6 vapor in an argon buffer gas. The dependence of probe beam absorption is observed by variation of beam intensity and spatial evolution. The simulation of an effective three-level energy model with velocity-changing collisions determines a collision rate that agrees with transmission data collected.

The electric dipole moment (edm) of the ground state of cesium has been measured using optical pumping and precision polarization analyzing techniques. The measured value of $d\sb{Cs}$ = ($-$1.8 $\pm$ 6.7 $\pm$ 1.8) $\times$ 10$\sp{-24}e \ cm$ implies that the electron edm $d\sb{e}$ = ($-$1.5 $\pm$ 5.5 $\pm$ 1.5) $\times$ 10$\sp{-26}e \ cm$. This result represents more than an order of magnitude improvement over all previous limits. The basic principle of the experiment is to spin polarize cesium atoms in a cell by optical pumping (along $\vec x$) using a laser tuned to the 6$S\sb{1/2}F$ = 3 $\to$ 6$P\sb{1/2}$ transition (8944 A) in the presence of an electric field $\vec E$ along $\vec z$. The edms oriented along $\vec x$ experience a torque due to the electric field along $\vec z$ and this results in a precession of the initial polarization in the plane perpendicular to $\vec E$. The precessed polarization is detected along $\vec y$ using another laser tuned to the 6$S\sb{1/2}F$ = 4 $\to$ 6$P\sb{1/2}$(8944 A). When the electric field is reversed, the precession is in the opposite sense. The magnetic field is maintained at zero at all times except for calibration. For small angles of precession, the change in the component of the polarization along $\vec y$, denoted by $\Delta P\sb{y}$, when the electric field is reversed is given by$$\Delta P\sb{y} = 2P\sb{x}\omega\sb{E}\tau = 2P\sb{x}\left\lbrack{2d\sb{Cs}E\over (2I + 1)\hbar}\right\rbrack \tau$$ $P\sb{x}$ is the initial polarization along $\vec x$, $\omega\sb{E}$ is the precession frequency due to the electric field, $\tau$ is the characteristic decay time of the polarization and $I$ = $7\over2$ the nuclear spin of the cesium atom. A measurement of such a polarization is thus a measurement of the edm of the cesium atom and the electron edm is derived from $d\sb{Cs} = Rd\sb{e},$ where $R$ the enhancement factor is theoretically calculated to be 120.0 $\pm$ 10.0.

<p> Observing the non-equilibrium dynamics of the invisible ultrafast atomic and sub atomic world requires optical tools with ultrashort bursts of light and wavelengths. Such optical sources can provide us with the ultimate understanding of the quantum universe in the 4D space-time continuum at femto-zeptosecond time and nano-picometer spatial scale. Revealing at the same time, the 'extra dimensions' of the chemical nature of matter with elemental specificity, e.g., oxidation, charge/spin localization to specific elements, etc. To expand the frontiers of knowledge, there is a simple solution: coherent ultrafast X-ray or gamma&ndash;ray laser light. Amongst the numerous X-ray light sources that exist or have been developed to date, there are just two practical complementary alternatives: giant free electron X-ray laser facilities and compact high harmonic generation X-ray lasers. This thesis focuses on the latter. </p><p> High harmonics result from the extreme nonlinear response of matter to strong laser fields. However, due to inability to phase match, the available bright HHG sources were limited to the EUV spectral region ~0.15<i> keV.</i> We report on two routes for efficiently obtaini bright, coherent X-ray light. The first approach, takes advantage of the ultra-high emission per atom and ion species, the large refractive indices, and small phase mismatch, using high intensity UV lasers. Here the specifics of the phase matching and group velocity matching lead to bright soft X-ray emission from ions and atoms, even at ionization levels above 500%. Using UV light at 0.270<i>&micro;m, </i> the harmonics extend above 280<i>eV</i> while the expec phasematching cutoff was believed to be 23<i>eV</i>. Second, using IR lasers, where the process o phase matching favors the coherent buildup of X-rays from many atomic emitters at high gas density over long distances at extremely low ionization levels. The X-rays supercontinua driven by Mid-IR light at &lambda;_L = 3.9<i>&micro;m,</i> extends over ~12 octaves to > 1.6<i>keV,</i> and broadest spectrum generated to date from any small or large source. Calculations indicate that we can extend further the emission to the hard X-ray region and beyond using high laser intensity UV-EUV lasers or low intensities IR-Far IR lasers, without significantly sacrificing the X-ray flux. However, special highly transmissive fibers are required for phase matching in the Mid-IR region, where the propagation distances are longer than the self-guiding lengths. In addition, the flux from the Mid-IR driven HHG is expected to decrease substantially or cease due to a large <i>v</i> vector &times; <i>B</i> vector drift of the returning electrons caused by th magnetic field <i> B</i> vector and because of the large quantum diffusion of the electron wavepacket. We propose and design special photonic bandgap waveguides to resolve all the issues limiting the flux of IR and Mid-IR and UV driven hard X-rays. </p><p> The properties of the X-rays, driven by UV and IR lasers, are completely contrasting: supercontinuum versus isolated sharply peaked harmonics, we predict chirped isolated single pulses on sub or femtosecond scale as opposed to near transform limited train of attosecond pulses, respectively for IR and UV-driven harmonics. While pressure phase matching has been widely used we introduce the concept of pressure-temperature tuned phase matching for the process of HHG generation that additionally increases the flux. </p><p> Moreover, we report on harmonic generation with extremely high flux at near <i>mW</i> and <i>&micro;J</i> level, that allows us to perform experiments, which were previously only possible in large-scale facilities. While a magnetic scattering cross section is orders of magnitude smaller than the charge scattering cross section, we demonstrate resonant magnetic ptychography coherent diffraction imaging at the <i>Fe, M</i>-edge, using narrow bandwidth X-rays light, to lo at buried magnetic domain structure. Using broad 'water window' and keV coherent X-ray supercontinua, we extract atomic structure on picometer spatial resolution and chemical bonds' information, through x-ray absorption spectroscopy measurements at various absorption edges. </p><p> Such unique light tools will make it possible to answer even questions that have not yet been asked or may have never been imagined.</p><p>