Browsing by Author "Killian, Thomas C."
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Item 3D optical lattice system for ultra-cold Lithium 6(2014-04-25) Yang, Tsung-Lin; Hulet, Randall G.; Killian, Thomas C.; Dai, PengchengOptical lattice experiments have proved to be a versatile tool for studying strongly correlated quantum systems. The motivation behind these experiments is to use the cold atoms to emulate a solid state system for which the Hamiltonian is analytically or numerically non-solvable. In our experiment, we construct a 3D simple cubic lattice system which realizes the Fermi-Hubbard model and provides us the opportunity to study the antiferromagnetic (AFM) insulator phase. In order to establish evaporative cooling in the optical lattice and to enlarge the size of the AFM phase, we implement a compensation potential additional to the standard lattice beam. In this thesis, I will present detailed steps to construct and calibrate the compensated 3D optical lattice system.Item 422 nm laser(2005) Simien, Clayton Earl; Killian, Thomas C.A 422 nm laser was constructed for the purpose of studying a strontium ultra-cold neutral plasma. Since strontium ions have atomic lines in the visible, we can optically image the plasma via the 88 Sr+ 2S1/2 → 2 P1/2 transition using 422 nm light. We produce light at this wavelength by converting infrared light at 844 nm from a commercial semiconductor infrared diode laser via second-harmonic generation in an semi-monolithic linear enhancement cavity. This thesis will cover the experimental details pertaining to nonlinear optics, optical resonator design, and locking electronics used to create a 422 nm laser.Item 461nm laser for studies in ultracold neutral strontium(2005) Saenz, Aaron D.; Killian, Thomas C.A 461 nm laser was constructed for the purposes of studying ultracold neutral strontium. The dipole-allowed 1 S0 → 1P1 transition at 460.862 nm can be used in laser cooling and trapping; optical imaging, Zeeman slowing, and photoassociative spectroscopy. We produce light at this wavelength by converting infrared light at 922nm from various IR sources, notably a Ti:Sapphire laser, via second harmonic generation in a frequency doubling cavity using a potassium niobate crystal. This thesis will discuss the motivation, optical resonator, locking electronics, and characterization of a 461 nm laser.Item A narrow linewidth diode laser system for strontium laser cooling applications(2004) Nagel, Sarah B.; Killian, Thomas C.The diode laser system for laser cooling on the 1S 0 → 3P1 intercombination line of strontium discussed in this thesis allows us to cool and trap an atomic strontium sample to 15 muK. Samples in this temperature range are useful for the development of the next generation of atomic frequency standards, cold collision studies, and as a step towards quantum degeneracy. This laser system consists of a Littrow configuration external-cavity diode laser, which is frequency locked to a high finesse cavity. The cavity is subsequently locked to an absorption feature to produce a few mW of tunable, stabilized, single mode power at the target wavelength. We present the design and characterization of this system, including a linewidth measurement of 70 kHz, as well as preliminary results from cooling and trapping.Item A New Optical Trap System for Ultracold Strontium(2013-12-04) Huang, Ying; Killian, Thomas C.; Hulet, Randall G.; Pu, HanAtoms can be trapped at the foci of intense laser beams, which can enable the study of interactions and dynamics of ultracold gases. In this thesis, we will describe our new trap designs. A large volume pancake-shaped optical dipole trap is initially used for loading large numbers of atoms from a Magneto-Optical Trap. A BEC with a large number of 84 Sr atoms has been achieved after evaporation in this trap. To form degenerate gas of 88 Sr we compress the mixture of 88 Sr and 87 Sr from the loading trap into a superimposed dimple trap. This combination improves the reproducibility of the experiment and shortens the time required to create quantum degenerate samples, while we are able to create 88 Sr BEC with high density. In order to generate BEC of 86 Sr, an isotope with large scattering length and extremely high three-body loss rate, we implement an optical sheet trap which has an aspect ratio of 1:10. The tight axis in the vertical direction provides strong potential to hold against gravity while the large horizontal dimension brings up the trap volume and keeps down the atomic density.Item Accessing Rydberg-dressed interactions using many-body Ramsey dynamics(American Physical Society, 2016) Mukherjee, Rick; Killian, Thomas C.; Hazzard, Kaden R.A.; Rice Center for Quantum MaterialsWe demonstrate that Ramsey spectroscopy can be used to observe Rydberg-dressed interactions in a many-body system well within experimentally measured lifetimes, in contrast to previous research, which either focused on interactions near Förster resonances or on few-atom systems. We build a spin-12 from one level that is Rydberg-dressed and another that is not. These levels may be hyperfine or long-lived electronic states. An Ising spin model governs the Ramsey dynamics, which we demonstrate can be used to characterize the Rydberg-dressed interactions. Furthermore, the dynamics can differ significantly from that observed in other spin systems. As one example, spin echo can increase the rate at which coherence decays. The results also apply to bare (undressed) Rydberg states as a special case, for which we quantitatively reproduce recent ultrafast experiments without fitting.Item An All Solid-State Laser System for Cooling and Trapping Lithium(2013-09-16) Revelle, Melissa; Hulet, Randall G.; Killian, Thomas C.; Morosan, EmiliaUltra-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.Item An Optical Lattice for Ultracold Strontium(2022-10-11) Wang, Chuanyu; Killian, Thomas C.; Pu, Han; Chen, SongtaoStrongly interacting many-body systems are of great interest in many areas of physics. Ultracold atoms in optical lattices are a powerful tool for creating and studying such systems. In this thesis, the construction and characterization of an 3D optical lattice for a ultra-cold Strontium apparatus is described. A 1064nm fiber amplified laser system is used to create three orthogonal pairs of standing waves that together form the 3D lattice. By delivering 4W of power to each arm of the lattice and focusing the beams to a beam radius of about 250 microns at the location of the atoms, we can create a 3D lattice with a maximum trap depth around 70 photon recoils.Item Assembly of a Three-Dimensional Multitype Bronchiole Coculture Model Using Magnetic Levitation(Liebert, 2013) Tseng, Hubert; Gage, Jacob A.; Raphael, Robert M.; Moore, Robert H.; Killian, Thomas C.; Grande-Allen, K. Jane; Souza, Glauco R.A longstanding goal in biomedical research has been to create organotypic cocultures that faithfully represent native tissue environments. There is presently great interest in representative culture models of the lung, which is a particularly challenging tissue to recreate in vitro. This study used magnetic levitation in conjunction with magnetic nanoparticles as a means of creating an organized three-dimensional (3D) coculture of the bronchiole that sequentially layers cells in a manner similar to native tissue architecture. The 3D coculture model was assembled from four human cell types in the bronchiole: endothelial cells, smooth muscle cells (SMCs), fibroblasts, and epithelial cells (EpiCs). This study represents the first effort to combine these particular cell types into an organized bronchiole coculture. These cell layers were first cultured in 3D by magnetic levitation, and then manipulated into contact with a custom-made magnetic pen, and again cultured for 48 h. Hematoxylin and eosin staining of the resulting coculture showed four distinct layers within the 3D coculture. Immunohistochemistry confirmed the phenotype of each of the four cell types and showed organized extracellular matrix formation, particularly, with collagen type I. Positive stains for CD31, von Willebrand factor, smooth muscle a-actin, vimentin, and fibronectin demonstrate the maintenance of the phenotype for endothelial cells, SMCs, and fibroblasts. Positive stains for mucin-5AC, cytokeratin, and E-cadherin after 7 days with and without 1% fetal bovine serum showed that EpiCs maintained the phenotype and function. This study validates magnetic levitation as a method for the rapid creation of organized 3D cocultures that maintain the phenotype and induce extracellular matrix formation.Item Bose-Einstein condensation of Strontium-84(2010) Martinez de Escolar, Yenny Natali; Killian, Thomas C.The achievement in 1995 of Bose-Einstein condensates (BEC) in dilute gases of alkali- metal atoms was one of the most important experimental results in recent times. Fifteen years later, the study of quantum fluids is a vibrant field exploring topics such as the effects of dimensionality and disorder on quantum fluids and the modeling of condensed-matter systems with BECs in optical lattices. This thesis describes the achievement of BEC in the alkaline-earth metal atom strontium (Sr). This new addition to the family of elements that have been Bose-condense opens new possibilities, such as the use of an optical Feshbach resonance to tune atom-atom interactions with relatively low atomic losses. Equally exciting theoretical proposals have been made for using quantum fluids made of alkaline-earth metal atoms, like creating exotic quantum magnetism states and demonstrating quantum computation in optical lattices. Previous efforts at achieving BEC with Sr focused on using the most abundant isotopes, 88Sr and 86Sr, without success. This thesis also describes our use of two-photon photoassociation spectroscopy (PAS) for accurate determination of the s-wave scattering length a (a measure of the interaction strength) for all the Sr isotopes and isotope mixtures. This result was essential for determining that bosonic 84Sr possesses the ideal collisional properties for efficient evaporative cooling to quantum degeneracy. 84Sr would not otherwise be the isotope of choice because its natural abundance is very low (0.6%). The PAS results also showed that 88Sr and 86Sr have unfavorable collision properties, which explains the difficulties encountered when attempting to form quantum degenerate 88Sr and 86Sr.Item Collective effects in ultracold neutral plasmas(2012) Castro Nieto, Jose Antonio; Killian, Thomas C.This thesis describes the measurements of collective effects in strongly coupled ultra-cold neutral plasmas (UNPs). It shows the implementation of experimental techniques that perturb either the density or velocity distribution of the plasma and it describes the subsequent excitation, observation and analysis of the aforementioned collective phenomena. UNPs are interesting in that they display physics of strongly coupled systems. For most plasma systems, collective effects are well described with classical hydrodynamic or kinetic descriptions. However, for strongly coupled systems, the Coulomb interaction energy between nearest neighbors exceeds the kinetic energy, and these descriptions must be modified as the plasma crosses over from a gas-like to liquid-like behavior. Strongly coupling can be found in exotic plasma systems found astrophysics, dusty plasmas, non-neutral trapped ion plasmas, intense-laser/matter interactions and inertial confinement fusion experiments. Compared to other strongly coupled plasmas, UNPs are ideal for studying collective effects in this regime since they have lower timescales, precisely controllable initial conditions and non-invasive diagnostics. Previous studies of UNPs concentrated on plasma expansion dynamics and some collective effects such as disorder induced heating, but little work had been done in relaxation or collision rates and collective modes in UNPs. This thesis presents a method for measuring collision rates by perturbing the velocity distribution of the plasma, observing plasma relaxation and measuring the relaxation rate. It also presents a new technique for observing collective modes in the plasma by perturbing the initial density of the plasma and how this results in the excitation of ion acoustic waves and a measurement of its dispersion relation. Finally, this thesis presents how this last technique can be used to create a gap in the center of the plasma and how this leads to hole propagation and plasma streaming and presents a characterization of both phenomena. The result of these experiments will be valuable for predicting the behavior of collective effects in other strongly coupled plasmas and for comparison with theories that describe them.Item Cool vibes(Nature Publishing Group, 2006-05-18) Killian, Thomas C.Item Creating Strontium Rydberg Atoms(2013-05-28) Zhang, Xinyue; Dunning, F. B.; Killian, Thomas C.; Natelson, DouglasDipole-dipole interactions, the strongest, longest-range interactions possible between two neutral atoms, cannot be better manifested anywhere else than in a Rydberg atomic system. Rydberg atoms, having high principal quantum numbers n>>1 and dipole moments that scale as n^2, provide a powerful tool to examine dipole-dipole interactions. Therefore, we have studied the production and production rates of strontium Rydberg atoms created using two-photon excitation and have explored their properties in two distinct experiments. In the first experiment, very-high-n (n~300) Rydberg atoms are produced in a tightly collimated atomic beam allowing spectroscopic studies of their energy levels and their Stark effects. Simulations using a two-active-electron model, developed by our theoretical collaborators, allow detailed analysis of the results and are in remarkable agreement with the experimental results. The high density of Rydberg atoms achieved ~ 5*10^5 cm^(-3), in this experiment will allow studies of strongly interacting Rydberg-Rydberg systems. The second experiment, in which a cold strontium Rydberg gas is excited in a magneto-optic trap, features an imaging technique offering both spatial and temporal resolution. We use this technique to observe and study the evolution of an ultra-cold strontium Rydberg gas which reveals the importance of Rydberg-Rydberg interactions in the early stages of this evolution. Strongly interacting Rydberg gas provides an opportunity to realize a very strongly-correlated ultra-cold plasma.Item Direct Water and Fat Determination in Two-Point Dixon Imaging(2013-09-16) Rambow, Olen; Clark, John W., Jr.; Ma, Jingfei; Killian, Thomas C.; Kelly, Kevin F.The Dixon technique is a well-established method in magnetic resonance imaging for obtaining separate images of water and fat. Here we present a generalized solution to the two-point Dixon problem with a geometric interpretation, allowing for flexible echo times and a multi-peak fat model. By simulation and experiment, we have analyzed the dependence on the echo times of the error in the water, fat, and relative background phasor values due to both signal noise and T2* decay. Furthermore, we have demonstrated that broken symmetry due to the multi-peak nature of fat enables direct water and fat determination without phase correction, and we have quantified the reliability of this technique as a function of the echo times. The results may provide valuable guidance for selecting scan parameters to balance the objectives of optimizing fat-water identification, minimizing error in the pixel values, and minimizing total scan time.Item Dynamics of Ion-Pair Formation in K(14p,20p)-SF6, CCl4 Collisions(2014-08-14) Kelley, Michael; Dunning, F. Barry; Killian, Thomas C.; Foster, MatthewCollisions between K(np) Rydberg atoms and electron attaching molecules can result in the creation of ion pairs through electron transfer. The mutual Coulomb attraction of these ions can lead to the formation of weakly-bound heavy-Rydberg ion-pair states orbiting at large radii. In this work, ion-pair states are created through collisions with SF6 and CCl4 in a small collision cell. These ion-pair states are allowed to drift into an analysis region where electric-field-induced dissociation allows for the velocity and binding energy distributions of these states to be determined. These distributions are analyzed through comparisons with the results of a Monte Carlo collision code. The data reveal that both CCl4 and SF6 form ion-pair states with long lifetimes and broad binding energy distributions, and their velocity distributions are strongly forward-peaked.Item Early time ion dynamics and progress towards laser cooling in an ultracold neutral plasma(2008) Simien, Clayton Earl; Killian, Thomas C.The progress toward laser cooling an ultracold plasma is presented in this thesis. Ultracold neutral plasmas are created by photo-ionizing laser cooled Strontium atoms. Initially this system is very strongly coupled, however the ions rapidly heat up leaving the plasma on the borderline of the strongly coupled regime. To counteract the effects of this heating an attempt to laser cool the ions in the system is undertaken. However, from these experiments we discovered that velocity changing collisions occurring in the system prevented laser cooling. In order to determine the collisions rate, a collision model was developed to simulate the spectra of the plasma from optical pumping experiments. These experiments and simulations in fact demonstrate that collisions are occurring at a fast enough rate to prevent ion cooling on the time scale of our experiment.Item Expansion and electron temperature evolution in an ultracold neutral plasma(2007) Gupta, Priya; Killian, Thomas C.This work describes the evolution of an ultracold neutral plasma as it expands freely in vacuum. It presents a comprehensive study of the electron temperature evolution under different initial conditions. Ultracold neutral plasmas are created by photoionizing laser-cooled neutral atoms in ultrahigh vacuum. The ions are typically at a temperature of ∼ 1K while the electron temperature can be set from 1--1000 K. After photoionization, some of the highly energetic electrons escape from the cloud, leaving a net positive charge in the cloud. This creates a Coulomb well which traps the rest of the electrons, and a plasma is formed. Since the electrons have a lot of kinetic energy, they tend to leave the cloud, however, the Coulomb force from the ion pulls the electrons back into the cloud. This exerts a recoil force on the ions, and the whole plasma starts expanding radially outwards. Since the expansion is caused by the thermal pressure of the electrons, a study of the plasma expansion unravels the complicated electron temperature evolution, under different initial conditions. Many collisional processes become significant as a plasma expands. These physical processes tend to heat or cool the ions and electrons, leading to very different kinds of evolution depending on the initial conditions of the plasma. This work demonstrates three different regions of parameter space where the degree of significance of these physical processes is different during the ultracold neutral plasma evolution. The experimental results are verified by theoretical simulations, performed by Thomas Pohl, which untangle the complicated electron temperature evolution.Item Experimental Study of Potassium and Strontium Rydberg Atoms - Chaotic Ionization, Quantum Optical Phenomena and Multiphoton Excitation(2014-04-24) Ye, Shuzhen; Dunning, F. Barry; Killian, Thomas C.; Brooks, Philip R.Very-high-n (n~300) Rydberg atoms serve as a powerful tool to study chaos and quantum optical phenomena. Measurements using a series of alternating impulsive kicks applied to potassium Rydberg atoms reveal that a phase space geometric structure called the turnstile governs the ionization process. Studies of the excitation spectra for potassium Rydberg atoms in a strong sinusoidal electric drive field in the radio frequency (100-300 MHz) regime, display quantum optical phenomena including electromagnetically induced transparency and Aulter-Townes splitting, and the data are well explained within the framework of Floquet theory. In order to study the strong dipole-dipole interactions between neutral atoms, new experimental techniques have been developed to create high densities of very-high-n (n~300-500) strontium Rydberg atoms using two- and three-photon excitation. The data demonstrate that high densities of strongly-polarized quasi-one-dimensional states can be produced and form the basis for further manipulation of the atomic wave functions. The strontium Rydberg states are modeled using a two-active-electron theory which produces results in good agreement with experimental observations.Item High Resolution Sculpting and Imaging of Ultracold Neutral Plasmas(2012-09-05) McQuillen, Patrick; Killian, Thomas C.; Si, Qimiao; Dunning, F. BarryThe sculpting of ultracold neutral plasmas represents a frontier in the experimental study of collective modes in strongly coupled plasmas. By extending the range of accessible length scales to less than tens of microns we gain access to a regime where The sculpting of ultracold neutral plasmas represents a frontier in the experimental study of collective modes in strongly coupled plasmas. By extending the range of accessible length scales to less than tens of microns we gain access to a regime where strong coupling's effects are predicted yet largely untested. To this effort, high resolution optical systems were designed, bench tested and implemented for sculpting and imaging ultracold neutral plasmas. Many complications and unexpected effects were documented to assist future experimental design considerations, including, those due to saturation and optical thickness, both of which limit the utility of 461 nm push beam modulations. It was concluded that sculpting should be performed on the 412 nm ionizing beam and real-time density space analysis is reliable for spatial frequencies up to 5 cyc/mm by using 4X magnified imaging. Higher spatial frequencies benefit from velocity space analysis due to extremely fast dynamics and low intensity levels.Item Interaction of Daptomycin with Lipid Bilayers Correlated to Its Action on Cell Membranes(2013-05-31) Chen, Yen-Fei; Huang, Huey W.; Toffoletto, Frank R.; Killian, Thomas C.Daptomycin is a lipopeptide antibiotic notably against multidrug-resistant, gram-positive pathogens. Evidence shows that the antibiotic acts neither on DNA nor on the proteins. It has been shown to insert and aggregate in the bacteria membrane; nevertheless, how the molecular interaction leads to cell death is unknown. In this work, the physical properties of interactions between daptomycin and model membranes are studied in order to understand the underlying mechanism of daptomycin. First, daptomycin’s binding affinity to membranes was found to be proportional to Ca++ concentration. The effect of Ca++ cannot be replaced by other divalent ions such as Mg++. After binding, daptomycin was found to form lipid-peptide aggregations on phosphatidylglycerol(PG)-containing vesicles. PG is required for the formation of lipid-peptide aggregates, which eventually lead to membrane ruptures. Cardiolipin, another main component in bacterial membrane, cannot substitute PG to induce the same membrane defect. In addition, with a fixed concentration of Ca++, it requires a minimum concentration of daptomycin to trigger the membrane defect process. The membrane defect results mainly from lipid-peptide aggregations rather than from pores forming in the membrane. Finally, x-ray data imply that daptomycin binds to the headgroup region of the bilayer, which causes membrane thinning. The elastic energy of membrane thinning elevates the energy level of the daptomycin binding state, which explains the transition to the aggregation state.