Relevant Degree Programs
Graduate Student Supervision
Doctoral Student Supervision (Jan 2008 - Nov 2020)
This dissertation presents work in the hyperpolarization of ¹²⁹Xe and in precision Xe spectroscopy using two-photon absorption. Both projects contribute to the development of optical magnetometry using ¹²⁹Xe. Motivating this work is the proposal for a new ¹²⁹Xe-based comagnetometer at TRIUMF for experiments searching for a permanent electric dipole moment of the neutron. In these proposed experiments ¹²⁹Xe will occupy the same experimental volume as ultracold neutrons and be used to measure drifts in an applied magnetic field. A scheme is described for optical magnetometry which involves the production of polarized ¹²⁹Xe followed by measurements using two-photon laser induced fluorescence as a probe. Spin exchange optical pumping is used to produce polarized ¹²⁹Xe, which is a necessary precursor for optical magnetometry. The first part of this dissertation presents the implementation and operation of a polarizer using a diode laser and a Xe-Rb-N₂-He mixture. We have achieved hyperpolarization of ¹²⁹Xe up to PXe ~ 5%, which is many times greater than the thermal equilibrium polarization. We measure the nuclear magnetic resonance signal from polarized ¹²⁹Xe using a low-field detection apparatus, and compare the signal with predictions based on a rate equation model. Efforts to optimize the degree of polarization in the present apparatus are described, as well as purification of Xe gas through freezeout.The second part of this dissertation presents precision spectroscopy on natural abundance Xe using a narrow linewidth laser. The two-photon transition studied here ( 5p⁵(²P₃/₂)6p²[3/2]₂ ← 5p⁶ (¹S₀)) is suitable to probe the ground state ¹²⁹Xe polarization for optical magnetometry. We present the implementation of a CW laser source with narrow linewidth followed by the excitation of Xe two-photon absorption in a resonant cavity. We measure and report hyperfine constants and isotope shifts from the observed laser induced fluorescence spectra. From the observed signal to noise ratio we estimate a magnetometric sensitivity based on this detection scheme over a range of Xe pressures. Results from this two-photon absorption measurement are essential in the determination of parameters for final implementation in the nEDM experiment.
Although many quantum mechanics problems of a point particle have been well understood, the realistic physical model is often a composite object consisting of particles bound together, and its quantum mechanics is an important problem with applications in many areas of physics. Unlike a point particle, a composite object possesses internal structure described by some degrees of freedom which are often entangled with each other. We call the entanglement among these degrees of freedom ``internal entanglement'', to distinguish it from any other entanglement they may share with an external object. Examples of internal entanglement include the entanglement between a vibrational and a rotational mode of a molecule, and that between its position and its internal clock-state etc.In this thesis, we study quantum mechanics of composite objects by focusing on the effects of internal entanglement. We first look at the tunnelling of a diatomic molecule type composite object through a half-silvered mirror in continuum space and observe that its spatial superposition state made by the mirror can decohere by emission of radiation due to the fact that its internal degrees of freedom are entangled with radiation fields, and that there exists entanglement between its position and its internal (i.e., relative position) degrees of freedom. Secondly, we study its lattice analog in molecular crystals, namely we replace the diatomic molecule by a biexicton, and the mirror by an impurity. We find that discreteness of a lattice makes the wave vector of a biexicton and the relative distance between two excitons of it entangled with each other. We investigate how this inseparability affects the creation of the biexciton-impurity bound states and the entanglement dynamics. Finally we propose a possible application of our study of internal entanglement to the Anderson model of a composite quasiparticle.
No abstract available.
Conventional Zeeman decelerator, consisting of 80 stages, was constructed and tested. The experimental setup was characterized using O₂ as the reference molecule. Known results of deceleration of O₂ were reproduced. As an extension, detailed REMPI analysis of deceleration of O₂ was carried out, this REMPI analysis was conducted in parallel with ref . Numerical simulation was successful in reproducing the TOF and REMPI spectra of deceleration of O₂.The extension of using Zeeman decelerator to decelerate a polyatomic radical, CH₃, was successful: from initial velocity of 480m/s to a final velocity of 368m/s, corresponding to a removal of 41.2% of the initial translational energy. The decelerator’s efficiency at final velocity of 368m/s is around ~10%. The limiting factor of further deceleration is the signal to noise ratio. Hence, optimization of DC discharge conditions of CH₃ were attempted, but the attempt was with limited success.
Master's Student Supervision (2010 - 2018)
The existence of amino acids in interstellar space has been a hot topic among researchers in astronomical science because of the biological molecules relevance to the origin of life. One of the most popular tools employed for the study of amino acids in relation to interstellar chemistry is matrix-isolation spectroscopy, as the cold and isolated environment provided by the matrix crystal mimics various astrophysical media such as interstellar ice. In the presented work, we reported the conformational and UV photochemistry studies of β-alanine and α-alanine via matrix-isolation Fourier transform infrared (MI-FTIR) spectroscopy in solid parahydrogen. This is the first time β-alanine and α-alanine have been registered in parahydrogen matrices, and the crystal has proven to be a more beneficial host over argon matrices for conformational analysis and in-situ UV irradiation experiment. Our claim on the superiority of solid parahydrogen is supported by the detection of high energy amino acids conformers in solid parahydrogen, which are unobserved in noble gas matrices. These conformers are conformer III for β-alanine, and conformer VI and V for α-alanine. As for UV irradiation experiment in solid parahydrogen, we obtained predominantly conformational change for β-alanine. However, α-alanine underwent complete photodestruction to give CO₂ and other unknown photoproducts we are still attempting to identify. Finally, we observed the possibility of β-alanine zwitterion formation in parahydrogen matrices, and are currently in the process of performing high accuracy quantum calculations on several β-alanine zwitterion conformers to assist us in spectral assignment.
The population dynamics of a Magneto-Optical Trap (MOT) make it a potential candidate for flux measurements of an atomic beam. This is achieved by determining the collisional cross section of the trapped atom and the beam particle which would result in ejection of a trapped atom. Due to the properties of a MOT it is possible to make spatial and time-of-flight profiles of the beam using this technique. The work of this thesis explores the collisional cross sections and flux profiles of several gaseous beams with a MOT of ⁸⁵Rb or ⁸⁷Rb. Each of the beams, generated through supersonic expansion, produced a loss cross section on the order of the combined van-der-Waals radii of the two particles. The flux and time-of-flight information of the beam was verified with a Residual Gas Analyser (RGA) and high beam rep rate pressure measurements. The MOT was characterized through a combination of fluorescence detection for population and a catalysis process for the trap's depth. A custom built translation mechanism for the MOT's optics and Helmholtz coils was constructed to perform the profiling measurements.
The main contribution of this project to the field of cold and ultracold molecules is we firstly demonstrated successful manipulation of the motion of polyatomic molecular beam in the rotational ground state, which has the lowest temperature of all possible states. Chapter 1 gives a summary of this field, including the application of cold and ultracold molecules, the methods to obtain them, and each method’s advantages and disadvantages. Once we decelerate molecular ensembles, we would like to trap the cold and ultracold molecules in electric trap, megnetic trap and megneto-optical trap. Chapter 2 starts with an introduction of the concept of supersonic beam and the basic knowledge of it, such as the specific features. The experimental setup will also be presented and explained in this chapter. The main highlight of this project is that we are manipulating molecules in the real ground state. Our molecular source is a Counter Rotating Nozzle(CRN), which can precool (or slow in alternate terminology) molecules in all states including the rotational ground state. The principle and performance of CRN will be presented and explained in Chapter 3. After obtaining a well precooled molecular beam, the microwave lens effect on various species is presented in Chapter 4. Meanwhile, the principle of AC Stark shift, AC dipole force and the microwave standing wave modes, such as TE modes and TM modes, will be explained in this chapter as well. Finally, I’ll summarize, draw conclusion of this work and describe the future expectation of this project in Chapter 5.
The ultimate goal of this research project is to develop an experiment to probe for superfluityin large clusters of molecular hydrogen in ultra-cold helium-4 nanodroplets. Superfluidityhas now been observed in a wide variety of systems and hydrogen is a good candidate toexhibit this macroscopic quantum phenomenon in a molecular system. In this thesis, twomajor advances were made enroute to the eventual search for superfluidity in bulk clustersof molecular hydrogen.1. In the first advance, the fluidity of supercooled molecular H₂ was investigated inhelium-4 nanodroples (~ 10⁵ atoms) at 0.38 K. To clearly demonstrate that the H₂clusters are fluxional, or fluid-like, separate studies of argon and neon clusters werealso made for comparison. To probe the behavior of the clusters, a single tetraceneprobe molecule was also inserted into the droplet and the laser induced fluorescence(LIF) from the tetracene was studied as a function of the cluster size and the pickupmethod. In the prior pickup method, the cluster species is added to the ⁴He dropletbefore to the probe molecule and in the post pickup method, the tetracene is addedand then the cluster species is added. Due to the difference in the pickup order, theconfiguration of the probe molecule and the cluster species can differ. The observedspectral shift of tetracene LIF in the presence of the cluster species was studied forboth pickup methods. For Ar and Ne clusters, the spectral shifts from the prior andpost pickup methods show clear differences. This observation suggests that for priorpickup, the tetracene molecule attaches to the surface of the cluster and does notpenetrate into the centre of the cluster and we conclude that the Ar and Ne clustersare not fluid-like in the helium droplets. For para-hydrogen and normal-hydrogen theLIF spectra of tetracene are independent of pickup order and we conclude that thesupercooled H₂ clusters remain fluid-like at 0.38 K.2. The second advance made in this thesis was to configure the droplet apparatus tostudy the rotational states of probe molecules in ⁴He droplets doped with H₂ clusters.The rotational states are studied by a combination of infrared and mass spectroscopy.Methane is the probe molecule used and when introduced into the ⁴He droplet it issurrounded by the H₂ cluster. If the surrounding H₂ liquid is superfluid, the methanerotates freely with a low moment of inertia. Conversely, if the H₂ remains a normalfluid, the dopant molecule drags hydrogen molecules along as it rotates and has a muchlarger moment of inertia. Rotationally resolved infrared spectroscopy of the methanegives clear information about the state of the surrounding supercooled liquid H₂. Asa first step, the v3 vibrational mode of bare methane in ⁴He droplets was studied. TheR(0) transition of the v3 stretching mode of methane was partially observed and foundto be consistent with the R(0) peak for CH⁴-doped ⁴He droplet systems previouslymeasured by the Miller group .