Preliminary Exam

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Events on Wednesday, December 13th, 2023

A Search for Vector-Like Leptons (VLLs)
Time: 2:30 pm - 4:30 pm
Place: 4272 Chamberlin
Speaker: Elise Chavez, Physics PhD Graduate Student
Abstract: The Standard Model is the current theoretical description of fundamental particles and their interactions. While it is able to describe the majority of phenomena that we observe, there are many that it cannot accommodate for. Such phenomena are dark matter, dark energy, and lepton non-universality. New theories have been proposed that extend the Standard Model in order to answer these long standing questions. One such extension is the 4321 model that predicts several new particles, one of which is the vector-like lepton (VLL). A search for pair produced vector-like leptons (VLLs) is proposed using the Run II data that was produced by proton-proton collisions at sqrt(s) = 13 TeV and collected by the Compact Muon Solenoid (CMS) at the Large Hadron Collider (LHC). In this search, the modes where the decays of the VLLs result in two Standard Model leptons are examined. This search employs a set of optimized kinematic selection criteria to enhance the signal, with respect to the Standard Model background, and a data based approach to determine the dominant ttbar background process. The goal of this search is to determine whether we see an excess of events in our data and set limits on the cross section of the VLL pair production.
Host: Tulika Bose
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Investigation of oxide defects and heterostructure modifications for use in quantum computing
Time: 3:30 pm - 5:30 pm
Place: B343 Sterling
Speaker: Emily Joseph, Physics PhD Graduate Student
Abstract: Si/SiGe quantum dots are attractive candidates for quantum computation yet there are significant challenges to overcome in an effort to improve the scalability of the system. These devices are susceptible to charge noise, some of which may arise from two-level systems (TLS) in the oxide. In this work we use resonator measurement and STEM images to investigate ALD oxide quality to improve semiconducting qubits. Another challenge inherent to Si/SiGe quantum dots is the energy splitting of the conduction band valley states. The valley splitting in Si devices is largely variable and unpredictable and it would be advantageous to be able to predictably rely on a designed-in valley splitting. A modification to the heterostructure has been produced with oscillating concentration of Ge through the quantum well, called the Wiggle Well. Theory predicts that this structure will show strong spin-orbit coupling and with shear strain can have a deterministically large valley splitting. Here we describe methods for mechanically introducing shear strain into the quantum well and a proposed experiment measuring the spin-orbit coupling of the Wiggle Well and making a Loss-DiVincenzo qubit without a micromagnet.
Host: Mark Eriksson
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