Physics Department Colloquia |
Events During the Week of March 10th through March 17th, 2024
Monday, March 11th, 2024
- No events scheduled
Tuesday, March 12th, 2024
- Theory of g factors in semiconductors -- some history, and new insights
- Time: 3:30 pm - 5:00 pm
- Place: Discovery Building, DeLuca Forum
- Speaker: David DiVincenzo, Forschungszentrum Jülich GmbH
- Abstract:
The g factor of electrons and holes in crystals and heterostructures of silicon, germanium, galium arsenide, etc., is a key parameter in designing spin qubits. I will begin by discussing two different but interrelated definitions of the g factor. Authors have disagreed from the beginning about whether or not g is a symmetric second-rank tensor. I will discuss that g, which is specific to each eigenstate, whether extended or localized, is best discussed in terms of three singular values associated with eigendirections, with a separate discussion about its sign. Luttinger gave a correct formula for the g factors of band electrons, including the orbital contributions arising from the spin-orbit interaction. But it was not until fifty years later, with the advent of Berry-curvature concepts, that his formula could be given a clear physical interpretation. I will show results of a survey we have done of band g factors in silicon and germanium, emphasizing new topological aspects. It is interesting that even silicon, with its very weak spin-orbit interaction, can, because of a combination of topology and symmetry, exhibit g factors very far from 2.
This event starts at 3:30pm with refreshments, followed at 3:45pm by a short presentation by Merritt Losert (PhD student Mark Friesen group), titled "Valley Splitting and Spin Shuttling in Si/SiGe Heterostructures". The invited presentation starts at 4pm.
Join Zoom Meeting Meeting ID: 979 1417 7653 Passcode: 874970
- Host: Mark Friesen
Wednesday, March 13th, 2024
- No events scheduled
Thursday, March 14th, 2024
- No events scheduled
Friday, March 15th, 2024
- Using Dissipation to Preserve Superconducting Qubit Coherence
- Time: 3:30 pm - 6:00 pm
- Place: 2241 Chamberlin Hall
- Speaker: Eli Levinson-Falk, USC
- Abstract: Superconducting qubits are a leading quantum information technology, combining high coherence, strong addressability, and flexible engineering. However, they are still prone to decoherence due to dissipative couplings to an uncontrolled environment. However, we can use dissipative coupling to a controlled environment to counteract decoherence and preserve the desired behavior. I will discuss some of our results using this approach, and focus on our recent development of a "dissipator" device that creates on-demand loss. By targeting this dissipation at a cavity, we can rapidly remove photons that might cause dephasing in a qubit coupled to the cavity. This dissipation both damps and refrigerates the target cavity, allowing for long-lived qubit coherence even when the bath temperature is high. I will discuss how to use this approach in a variety of applications, including both operating large-scale quantum processors and studies of foundational quantum mechanics.
- Host: Maxim Vavilov