Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006. / Source: Dissertation Abstracts International, Volume: 67-07, Section: B, page: 3850. Adviser: Vijay Pandharipande. Includes bibliographical references (leaves 118-122) Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007. / Source: Dissertation Abstracts International, Volume: 69-02, Section: B, page: 1302. Adviser: George H. Miley. Includes bibliographical references (leaves 156-161) Available on microfilm from Pro Quest Information and Learning.

In this thesis, new acquisition and analysis methods are described for multinuclear magnetic resonance spectroscopy (MRS) for the quantification of brain metabolites at ultra high magnetic field strengths (7T). An analytical model was derived for the optimisation of the stimulated echo acquisition mode (STEAM) sequence timing parameters for lactate detection. The effects of the chemical shift displacement artefact on the J-modulated signal for a weakly-coupled spin system were considered in the three applied directions of field gradients and the product operator formalism was used to obtain expressions for the signal modulation in each compartment of the excited volume. The validity of this model was demonstrated experimentally in a phantom and acquisitions with optimised parameters were performed on a healthy volunteer. The spectra acquired with an echo time (TE) of 144 ms and with an optimised mixing time and TE of 288 ms showed easily detectable lactate peaks in the normal human brain. Additionally, the acquisition with the longer TE resulted in a spectrum with less lipid/macromolecular (MM) contamination. The simulations demonstrated that the proposed analytical model is suitable for correctly predicting the resulting lactate signal. With the optimised parameters, it was possible to use a simple sequence with sufficient signal-to-noise ratio (SNR) to reliably distinguish lactate from overlapping resonances in a healthy brain at ultra high-field. Estimation of metabolic changes during neuronal activation represents a challenge for in vivo MRS, especially for metabolites with low concentration and signal overlap, such as lactate. This thesis also includes work focused on the reliable quantification of lactate during a paradigm with 15 minutes of visual stimulation. The lipid and MM signals were significantly reduced by using a long TE (144 ms) sequence and the remaining MM signals in the vicinity of the lactate peak were individually fitted with simulated Lorentzian peaks, to ensure a good fit of the inverted lactate doublet. Statistically significant changes in lactate (~10%) and glutamate (~3%) levels during stimulation were detected in the visual cortex and agree with previous measurements. Furthermore, the use of a prolonged stimulation period unveiled a distinctive metabolic response pattern, which can provide further insight into brain activation mechanisms. 13C MRS combined with the infusion of labelled substrates is able to provide unique information on the relationship between neuroenergetics and brain function. However, the lack of sensitivity associated with the general complexity of 13C experiments has hampered its widespread use for research into human brain disease. In this study, a new methodology for acquisition and analysis of 13C signal is presented for the study of neuroenergetics and neurotransmission in a deep brain structure - anterior cingulate cortex - that is thought to play a major role in the processing of sensory information and can be impaired in patients with schizophrenia. In vitro testing was performed to evaluate the performance of the implemented sequence for signal localisation and polarisation transfer, both proving adequate for the intended purpose. In vivo data were acquired in four subjects, one diagnosed with early schizophrenia, with a protocol which involved 60 minutes of infusion of [1-13C]glucose. Turnover curves for the labelled products were generated from the dynamic 13C spectra with a temporal resolution of 10 minutes and were in agreement with the ones obtained from rodent experiments. Therefore, the feasibility of 13C experiments for the study of psychosis was here demonstrated, taking advantage of the increase in SNR at ultra high-field for determination of metabolic fluxes.

This thesis describes experimental work done with two of the smallest diatomic alkali molecules, 6Li2 and 23Na6Li, each formed out of its constituent atoms at ultracold temperatures. The 23Na6Li molecule was formed for the first time at ultracold temperatures, after previous attempts failed due to an incorrect assignment of Feshbach resonances in the 6Li+23Na system. The experiment represents successful molecule formation around the most difficult Feshbach resonance ever used, and opens up the possibility of transferring NaLi to its spin-triplet ground state, which has both magnetic and electric dipole moments and is expected to be long-lived. For 6Li2, the experimental efforts in this thesis have solved a long-standing puzzle of apparently long lifetimes of closed-channel fermion pairs around a narrow Feshbach resonance, finding that the lifetime is in fact short, as expected in the absence of Pauli suppression of collisions. Moreover, measurements of collisions of Li2 with free Li atoms demonstrates a striking first example of collisions involving molecules at ultracold temperatures described by physics beyond universal long-range van der Waals interactions.

Nitrogen-vacancy (NV) centers in diamond have recently emerged as a promising new system for quantum information and nanoscale sensing applications. They have long coherence times at room temperature and can be positioned in proximity to the diamond surface, enabling magnetometry with high spatial resolution and coherent coupling to other quantum systems. This thesis presents three experiments in which single NV centers were used to sense magnetic fields at the nanometer scale. In the first experiment, the coherent evolution of a single NV spin is coupled to the motion of a magnetized mechanical resonator tens of nanometers from the NV. Coherent manipulation of the spin is used to sense the driven and Brownian motion of the resonator under ambient conditions, with picometer-scale sensitivity to motion. Future applications of this technique include the detection of the zero-point fluctuations of a mechanical resonator, the realization of strong spin-phonon coupling at a single quantum level, and the implementation of quantum spin transducers. In the second experiment, a single NV electronic spin is used to measure the quantum dynamics of distant individual nuclear spins from within a surrounding spin bath. The demonstrated sensing technique dramatically increases the potential size of NV based quantum registers for quantum information applications, and provides a new method for nanoscale magnetic resonance imaging of single nuclear spins. In the third experiment, single NV electronic spins are used to probe magnetic Johnson noise in the vicinity of conductive silver films. Measurements of polycrystalline silver films over a range of distances (20-200 nanometers) and temperatures (10-300 Kelvin) are consistent with the classically expected behavior of the magnetic fluctuations. However, Johnson noise is found to be dramatically suppressed next to single-crystal films, indicative of a substantial deviation from Ohm's law arising from the ballistic motion of the electrons in the metal. These result demonstrate that our technique provides a general, non-invasive probe of local electron transport in samples of arbitrary size and dimensionality, which can be used to explore materials response to localized impurities and the interplay between transport, interactions and disorder at the nanoscale. / Physics

Experiments with ultracold atoms in optical lattices provide outstanding opportunities to realize exotic quantum states due to a high degree of tunability and control. In this thesis, I present experiments that extend this control from global parameters to the level of individual particles. Using a quantum gas microscope for 87Rb, we have developed a single-site addressing scheme based on digital amplitude holograms. The system self-corrects for aberrations in the imaging setup and creates arbitrary beam profiles. We are thus able to shape optical potentials on the scale of single lattice sites and control the dynamics of individual atoms. We study the role of quantum statistics and interactions in the Bose-Hubbard model on the fundamental level of two particles. Bosonic quantum statistics are apparent in the Hong-Ou-Mandel interference of massive particles, which we observe in tailored double-well potentials. These underlying statistics, in combination with tunable repulsive interactions, dominate the dynamics in single- and two-particle quantum walks. We observe highly coherent position-space Bloch oscillations, bosonic bunching in Hanbury Brown-Twiss interference and the fermionization of strongly interacting bosons. Many-body states of indistinguishable quantum particles are characterized by large-scale spatial entanglement, which is difficult to detect in itinerant systems. Here, we extend the concept of Hong-Ou-Mandel interference from individual particles to many-body states to directly quantify entanglement entropy. We perform collective measurements on two copies of a quantum state and detect entanglement entropy through many-body interference. We measure the second order Rényi entropy in small Bose-Hubbard systems and detect the buildup of spatial entanglement across the superfluid-insulator transition. Our experiments open new opportunities for the single-particle-resolved preparation and characterization of many-body quantum states. / Physics

Diatomic molecules are considered good candidates for the study of strongly correlated systems and precision measurement searches due to their combination of complex internal states and strong long-range interactions. Cooling molecules down to ultracold temperatures is often a necessary step for fully utilizing the power of the molecule. This requires a trap for molecules and the ability to cool molecules to the mK regime and below. A magneto-optical trap (MOT) is a good tool for achieving mK temperatures. However, extra care is needed for molecules to form the necessary quasi-closed cycling transitions due to molecule's complicated energy structure. In our work with CaF, we use two repump lasers to block vibrational leakage and selection rules for the rotational degree of freedom to achieve about 10^{5} photon cycles. The two-stage buffer gas beam source is a general method to generate a cold and slow beam of molecules with a forward velocity of about 50 m/s. The compatibility of the buffer-gas source with a MOT is studied and we confirm that such beams can be nicely compatible with MOTs using various atomic species. In order to load molecules into a MOT from even such a slow beam, additional slowing is required due to the low capture velocity of a molecular MOT (< 10 m/s). We apply a frequency-broadened “white-light” slowing on CaF from a two-stage source, demonstrating slowing of CaF below 10 m/s. An AC MOT, which provides active remixing of dark substates, is also developed and Li atoms are slowed and trapped. These are crucial ingredients for co-trapping CaF molecules and Li atoms and study their collisional properties, which would lead to sympathetic cooling of molecules down to ultracold temperatures. The achievement of slowing and development of this system allowed for the detailed study of the CaF laser cooling system, as well as physical processes involved with AC MOTs and the proposed MOT for CaF. Crucial knowledge of this archetypal system provides significant progress toward manipulation and control of molecules similar to what has been achieved with atoms and what is necessary for searches for new physics with ultracold molecules. / Physics

Significant sub-systems were created and others enhanced providing a platform for an order of magnitude precision increase of the small 4He interval - 23P1→23P2 laser spectroscopy measurement, as well as other helium transitions. These measurements serve as tests of helium theory and quantum electro-dynamics in general. Many improvements to the original experiment are discussed and characterized. In particular, counting speed increased 10x, the signal level was doubled, a novel Doppler shift minimization technique was implemented, a control node re-architecture was realized along with many useful features, and the development environment was updated. An initial 28% precision improvement was achieved also providing a foundation for additional gain via a created smaller and more heavily windowed vacuum cavity and picomotor controls.

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