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Events on Monday, December 12th, 2022

Preliminary Exam
Superconductor-semiconductor hybrid systems for quantum computing applications
Time: 10:00 am
Place: B343 Sterling
Speaker: Ben Harpt, Physics Graduate Student
Abstract: In the global pursuit to develop quantum computers with unprecedented problem-solving capabilities, success hinges upon engineering platforms that are both controllable and scalable. Superconductors and semiconductors are, individually, among the most promising materials platforms for building a solid-state quantum processor. However, combing the advantages of both materials to build hybrid quantum devices unlocks yet further potential. In this talk, I overview the physics of ‘super-semi’ hybrid systems and discuss how it forms a basis for new technologies in quantum computing. I focus in detail on two diverse applications which are the primary focus of my doctoral research: (1) superconducting resonators used for readout of quantum dot qubits; and (2) qubits formed from Josephson junctions in proximitized germanium heterostructures. In the former example, I show completed work identifying and utilizing a little-known coupling mechanism between the qubit and the resonator. In the latter, I demonstrate early progress toward developing devices and outline a pathway for future research. Studying these and other super-semi hybrid systems offers fruitful new physics and technologies for scaling up quantum computers.
Host: Mark Eriksson
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Plasma Physics (Physics/ECE/NE 922) Seminar
"Heat and particle transport in the JET DT2 campaign"
Time: 12:00 pm
Place: 1610 Engineering Hall
Speaker: Philip Schneider, IPP Garching
Abstract: Heat and particle transport in tokamak plasmas changes with isotope mass (H, D, T) in such a way that a satisfying theoretical description eludes us to this day.

However, now we at least better understand why we are not able to formulate such a theory. The main ion mass is connected to a large variety of physical mechanisms which will vary in importance for different plasma regimes. The resulting system is determined by the non-linear coupling between transport channels particles and heat, electrons and ions as well as regions within the plasma like the core and the edge (pedestal). In experiments a change of the isotope mass often results in a shift of plasma regime and the isotope mass dependence that you want to measure consequently competes with the impact of variations in other parameters.

The JET tokamak recently dedicated a considerable amount of time to address this issue from multiple angles. A series of dedicated experiments got prepared to ensure that the isotope mass dependencies can be accurately determined. In the edge of H-mode plasmas we find the confinement to scale with mass where H is worst and T best. However, this changes in the core, here H and D are found with matching confinement while T and DT plasmas consistently have better core confinement. Flux-driven simulations with ASTRA using the quasilinear TGLF-SAT2 model and local linear and non-linear gyrokinetic simulations can capture certain aspects of the observation, but also highlight gaps in the models - in particular, with the electromagnetic stabilisation.

Dr. Philip A. Schneider studied physics at the LMU in Munich did his PhD on tokamak edge transport barriers at the Max-Planck-Institute for Plasma Physics in Germany. He worked the last 14 years on data from ASDEX Upgrade, DIII-D, JET and TCV with a focus on heat transport, confinement and fast ions in tokamak plasmas. Currently, he is coordinator of the task "isotope effects on confinement and transport" in the JET DT2 campaign.
Host: ECE/NE/PHYSICS 922 Seminar in Plasma Physics
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