Physics and Astronomy
http://hdl.handle.net/10315/28582
2020-08-10T08:42:36ZThe Strong Isospin-Breaking Correction to the Leading-Order Hadronic Vacuum Polarisation Contribution to the Anomalous Magnetic Moment of the Muon
http://hdl.handle.net/10315/37481
The Strong Isospin-Breaking Correction to the Leading-Order Hadronic Vacuum Polarisation Contribution to the Anomalous Magnetic Moment of the Muon
James, Christopher Lewis
The contribution of strong isospin-breaking (SIB) effects to the value of the anomalous magnetic moment of the muon is studied using the leading-order SIB component of the photon vacuum polarisation function, calculated in Chiral Perturbation Theory (ChPT) in the low Euclidean momentum-squared regime. At two-loop order in ChPT the result is found to be aSIB= 0.82(12)1010, approximately 1 order of magnitude less than recent determinations using Lattice Quantum Chromodynamics (QCD) and also phenomenology. It is shown that the inclusion of a tree-level term from next-to-next-to-next-to leading order (NNNLO) raises the ChPT prediction to aSIB= 3.61(98)1010. This result is consistent with the most precise result from Lattice QCD. The dominant NNNLO contribution is interpreted as parameterising the SIB physics of the lightest resonances which are predicted to be the most significant processes at low momentum.
2020-05-11T00:00:00ZExact Gate Decompositions for Photonic Quantum Computers
http://hdl.handle.net/10315/37435
Exact Gate Decompositions for Photonic Quantum Computers
Kalajdzievski,Timjan Zorboski
The purpose of this work is to examine the use of decompositions on a continuous-variable quantum computer by both implementing and examining known methods, as well as to expand on them by developing my own. I detail the usage of known and new techniques for gate decompositions in some useful quantum algorithms such as simulating bosonic particles in a optical lattice, and solving differential equations with broad applications in other scientific fields. The new methods detailed in this work provide decompositions for continuous variable quantum computers which no longer require approximations. These methods rely on strategically using unitary conjugation and a lemma to the Baker-Campbell-Hausdorff formula to derive new exact decompositions from previously known ones, leading to exact decompositions for a large class of gates. I also demonstrate how exact decompositions can be employed in a wide range of algorithms, while requiring much fewer gates (sometimes as many as order-of-magnitude less) than equivalent decompositions with other methods. This work can potentially further bridge the gap between what is required to perform algorithms on a quantum computer and what can be done experimentally.
2020-05-11T00:00:00ZDevelopment and Characterization of Auto-Locked Laser Systems and Applications to Photon Echo Lifetime Measurements
http://hdl.handle.net/10315/37390
Development and Characterization of Auto-Locked Laser Systems and Applications to Photon Echo Lifetime Measurements
Beica, Hermina
We have developed and characterized a new class of vacuum-sealed, auto-locking diode laser systems with an auto-locking controller that allows these instruments to be operated with greater ease and control at desired wavelengths in the visible and near-infrared spectral range. These laser systems can be tuned and frequency stabilized with respect to atomic, molecular, and solid-state resonances without human intervention using a variety of control algorithms programmed into the same controller. We show that these lasers have exceptional long-term stability, with an Allan deviation (ADEV) floor of 210^{-12}, and a short-term linewidth of 200 kHz. These performance characteristics are related to reducing current noise and ensuring vacuum sealing. We demonstrate accurate measurements of gravitational acceleration at the level of a few parts-per-billion by incorporating the laser into an industrial gravimeter. We also realize
the basis of a LIDAR transmitter that can potentially operate in a spectral range in which frequency references are not readily available. We have also developed a technique for precise measurements of atomic lifetimes using optical photon echoes. We report a measurement of 26.10(3) ns for the 5^2P_{3/2} excited-state in ^{85}Rb vapour that has a statistical uncertainty of 0.11% in 4 hours of data acquisition. We show that the best statistical uncertainty that can be obtained with the current configuration is 0.013%, which has been exceeded by only one other lifetime measurement. An analysis of the technical limitations based on a simple model shows that these limitations can be overcome using a feedback loop with a reference
interferometer. Our studies indicate that it should be possible to investigate systematic effects at the level of 0.03% in 10 minutes of data acquisition. Such an outcome could potentially result in the most accurate measurement of any atomic lifetime.
2020-05-11T00:00:00ZEffects of Ultrathin Interlayers on Thermal Boundary Conductance at Metal-Dielectric Interfaces
http://hdl.handle.net/10315/36683
Effects of Ultrathin Interlayers on Thermal Boundary Conductance at Metal-Dielectric Interfaces
Oommen, Shany Mary
Heat transport in micro- and nano-scale materials have an increasingly important role in thermal management of numerous technologies such as thermoelectric energy conversion, microelectronics, and plasmonic devices. Understanding the heat transport contributions from the interface is crucial when interfacial resistance forms a significant fraction of the total thermal resistance of the device.
In this thesis, we analyze the modification of thermal conductance at metal-dielectric interfaces by inserting few-nanometer thick metal interlayers. A thickness-dependent interlayer study suggests that interfacial conductance alters significantly at ultrathin thicknesses before reaching a plateau. Our results reveal that the electron-phonon coupling strength of an interlayer plays a significant role in determining the overall thermal boundary conductance. Analysing heat transport mechanisms across a variety of metal-dielectric interfaces by means of an interlayer indicated that thermal boundary conductance depends on an interplay between the phonon vibrational properties and metal electron-phonon coupling strength overlap.
2019-11-22T00:00:00Z