Event Time: Friday, July 19, 2019 | 10:00 am - 12:00 pm
Event Location:
Room 309, Hennings Bldg
Add to Calendar 2019-07-19T10:00:00 2019-07-19T12:00:00 Departmental Oral Examination (Thesis Title: "High Resolution Two-Photon Spectroscopy of 129Xe for Precision Optical Magnetometry") Event Information: Abstract: This dissertation presents high precision two-photon xenon spectroscopy of the 5p5(2P3/2)6p 2[3/2]2 -> 5p6 (1S0) transition. Experimental results of the spectroscopic signal over pressures of 15 980 mTorr, combined with a theoretical discussion, led to the determination of the natural linewidth of the excited state. Specific attention is payed to the (F = 3/2) hyperfine level of 129Xe, motivated by the new experiment at TRIUMF to measure the electric dipole moment of the neutron (nEDM), where 129Xe will be used as an optical comagnetometer. A non-zero value of the nEDM would partially confirm the existence of the baryon asymmetry in the universe as predicted by the standard model. The experiment at TRIUMF aims increase the sensitivity of the current nEDM limit by increasing the number of ultra-cold neutrons and employing a cohabiting 199Hg/129Xe dual species comagnetometer. The first experimental success was the technological development of the continuous wave 252 nm ultra-violet (UV) laser system, with the power and precision to selectively probe the hyperfine levels of 129Xe. Using this laser system the first high resolution spectrum of the two-photon transition was measured. Ten transition peaks are observed for the six most abundant isotopes in xenon gas, along with the hyperfine levels of the 129Xe and 131Xe isotopes. Analysis of this spectrum led to direct determinations of the hyperfine constants of the 5p5(2P3/2)6p2[3/2]2 excited state and constants relating to the isotope shift. The final part of the dissertation focused on the parameterization of the 129Xe (F = 3/2) spectral line. In the nEDM experiment the pressure of 129Xe is limited to 3 mTorr, making it essential to characterize the signal at this level in order to maximize the sensitivity of the comagnetometer. This work presents a pressure dependence study of the spectral lineshape from 980-15 mTorr. These results illustrate the expected signal size and relative transition frequency to the (F = 3/2) level for precision laser tuning. In addition to the contributions of this work to optical magnetometry, the results present a complimentary experimental technique to determine the natural linewidth of the 5p5(2P3/2)6p2[3/2]2 excited state. The high precision of the results permit extrapolation of the lineshape to zero pressure yielding a natural linewidth of 4.3(1.6) MHz/Torr. Overall, the work presented is significantly important to optical magnetometry in nEDM experiments, as well as to precision spectroscopy and theories of atom-atom interactions. Event Location: Room 309, Hennings Bldg
Event Time: Thursday, July 25, 2019 | 1:00 pm - 3:00 pm
Event Location:
Room 203, Graduate Student Centre (6371 Crescent Road)
Add to Calendar 2019-07-25T13:00:00 2019-07-25T15:00:00 Final PhD Oral Examination (Thesis Title: “Aspects of Quantum Information in Quantum Field Theory and Quantum Gravity”) Event Information: Abstract: We discuss applications of quantum information theoretic concepts to quantum gravity and the low-energy regime of quantum field theories. The first part of this thesis is concerned with how quantum information spreads in four-dimensional scattering experiments for theories coupled to quantum electro- dynamics or perturbative quantum gravity. In these cases, every scattering process is accompanied by the emission of an infinite number of soft photons or gravi-tons, which cause infrared divergences in the calculation of scattering probabilities. There are two methods to deal with IR divergences: the inclusive and dressed formalisms. We demonstrate that in the late-time limit, independent of the method, the hard outgoing particles are entangled with soft particles in such a way that the reduced density matrix of the hard particles is essentially completely decohered. Furthermore, we show that the inclusive formalism is ill-suited to describe scattering of wavepackets, requiring the use of the dressed formalism. We construct the Hilbert space for QED in the dressed formalism as a representation of the canonical commutation relations of the photon creation/annihilation algebra, and argue that it splits into superselection sectors which correspond to eigenspaces of the generators of large gauge transformations. In the second part of this thesis, we turn to applications of quantum information theoretic concepts in the AdS/CFT correspondence. In pure AdS, we find an explicit formula for the Ryu-Takayanagi (RT) surface for special subregions in the dual conformal field theory, whose entangling surface lie on a light cone. The explicit form of the RT surface is used to give a holographic proof of Markovicity of the CFT vacuum on a light cone. Relative entropy of a state on such special subregions is dual to a novel measure of energy associated with a timelike vector iiiflow between the causal and entanglement wedge. Positivity and monotonicity of relative entropy imply positivity and monotonicity of this energy, which yields a consistency conditions for solutions to quantum gravity. Event Location: Room 203, Graduate Student Centre (6371 Crescent Road)
Event Time: Monday, July 29, 2019 | 8:00 am - 10:00 am
Event Location:
ISAC-II Room 223 (TRIUMF)
Add to Calendar 2019-07-29T08:00:00 2019-07-29T10:00:00 Departmental Oral Examination (Thesis Title: "Dawning of Nuclear Magicity in N=32 Seen Through Precision Mass Spectrometry") Event Information: Abstract: In the early days of nuclear science, physicists were astounded that specific "magic" combinations of neutrons or protons within nuclei seemed to bind together more tightly than other combinations. This phenomenon was related to the formation of shell structures in nuclei. More recently, nuclear shells were observed to emerge or vanish as we inspect nuclei further from stability. The structural evolution of these changing shells has been the object of intense experimental investigation, and their behavior has become a standard ruler to benchmark theoretical predictions. In this work, we investigated the emergence of shell effects in systems with 32 neutrons (N=32) using mass spectrometry techniques. Evidence for "magicity" was observed in potassium (with 19 protons, or Z=19), calcium (Z=20) and scandium (Z=21), but not in vanadium (Z=23) and heavier elements. In between, the picture at titanium (Z=22) was unclear. We produced neutron-rich isotopes of titanium and vanadium through nuclear reactions at the ISAC facility and measured their atomic masses at the TITAN facility, in the TRIUMF Laboratory in Vancouver.  These measurements were performed with the newly commissioned Multiple-Reflection Time-of-Flight Mass Spectrometer at TITAN facility and were substantiated by independent measurements from the Penning trap mass spectrometer. The atomic masses of 52Ti to 55Ti and 52V to 55V isotopes were measured with high precision, right at the expected emergence of N=32 shell effects.  Our results conclusively establish the existence of weak shell effects in titanium and confirm their absence in vanadium, narrowing down the precise onset of this shell closure. Calculations of the N=32 nuclear shell are within reach of the so-called "ab initio" theories. In these, complex atomic nuclei are described theoretically from fundamental principles, by applying principles of Quantum Chromodynamics to many-body quantum methods. Our data were compared with a few state-of-the-art ab initio calculations which, despite very successfully describing the N=32 shell effects in Ca and Sc isotopes, overpredict its strength in Ti and erroneously assign V as its point of appearance. We hope the deficiencies revealed by our work will guide the development of the next generation of ab initio theories. Event Location: ISAC-II Room 223 (TRIUMF)
Event Time: Monday, July 29, 2019 | 1:00 pm - 3:00 pm
Event Location:
Room 301, Hennings Bldg
Add to Calendar 2019-07-29T13:00:00 2019-07-29T15:00:00 Departmental Oral Examination (Thesis Title: "Exploring the tumour microenvironment with non-invasive magnetic resonance imaging (MRI) techniques") Event Information: Abstract: This thesis comprises development and application of several MRI techniques to improve our understanding of tumour growth, drug distribution, and drug effect using pre-clinical tumour models in mice. In the first part of the thesis, a novel high molecular weight contrast agent, HPG-GdF is introduced. This molecule is a hyperbranched polyglycerol labeled with an MRI contrast agent (Gd-DOTA) as well as a fluorescent tag. After injecting the agent into mice within an MRI scanner, contrast-agent kinetics were quantified using a two-parameter linear model and validated with quantitative immunohistochemistry via direct fluorescence imaging of HPG-GdF. HPG-GdF was used to assess whether vascular function plays a role in how a chemotherapy (Herceptin) distributes within a tumour. Tumour vessel permeability and fractional plasma volume were quantified using the HPG-GdF and no relationship was found between vascular function and presence of drug. HPG-GdF was then applied to show that Avastin (an antiangiogenic agent) decreased vessel permeability in tumours. Using histological methods, a dramatic reduction in hypoxia (oxygen deficiency in tissues) was observed in treated tumours. Unfortunately, existing MRI methods to evaluate oxygenation were time-intensive and lacked sensitivity. In the second part of this thesis, we introduce, develop, validate, and apply a new method to assess tumour oxygenation using MRI. Oxygen (O2) is a paramagnetic molecule that shortens the longitudinal relaxation time (T1) of protons in MRI. This subtle effect has been widely reported in the literature but its applications in cancer have been limited. Our technique - dynamic oxygen-enhanced MRI (dOE-MRI) - uses T1 weighted signal intensity images acquired during a cycling gas challenge (air or oxygen) and independent component analysis (ICA). Hypoxia staining with pimonidazole correlated strongly with dOE-MRI values in a murine tumour model (SCCVII) and only weakly in a colorectal xenograft model (HCT-116). Finally, we provide compelling evidence that treatment with Avastin improves tumour oxygenation in subcutaneous tumours. With dOE-MRI the sensitivity and speed of existing techniques was greatly improved. Since our technique requires no injectable contrast agent, special sequences or hardware, we anticipate that this technique can be quickly translated into the clinic. Event Location: Room 301, Hennings Bldg