Events at Physics |
Events on Friday, October 25th, 2024
- Thesis Defense
- Alloy disorder, valley splitting, and shuttling for spin qubits in Si/SiGe heterostructures
- Time: 1:00 pm - 3:00 pm
- Place: 5310 Chamberlin Hall;
- Speaker: Merritt Losert, Physics PhD Graduate Student
- Abstract: Spin qubits in Si/SiGe heterostructures have several advantages as scalable qubit platforms, including their small size, their long coherence times, and their reliance upon conventional semiconductor fabrication methods. However, microscopic disorder in the semiconductor structure impact these qubits in a variety of ways, reducing qubit yield. In particular, the valley energy splitting (the energy gap between the two low-lying conduction band valley states) is widely variable, and highly sensitive to microscopic disorder. In this dissertation, we study the effects of disorder on spin qubits formed from quantum dots in Si/SiGe heterostructures, focusing particularly on the valley energy splitting. We demonstrate that alloy disorder (disorder due to the random arrangement of Si and Ge atoms in the SiGe alloy) has a profound impact on these qubits. We develop a theory to explain the impact of alloy disorder on the valley splitting, and we compare the results of this theory to a variety of experiments, finding good quantitative agreement. We demonstrate that alloy disorder determines the valley splitting in most realistic devices, and we propose a high-Ge heterostructure that enhances alloy disorder in order to increase average valley splittings. We also examine the impact of alloy disorder on long-distance qubit connectivity via conveyor-mode electron shuttling. We demonstrate that alloy disorder leads to valley excitations, causing quantum information to leak out of the qubit subspace. We develop a variety of schemes to mitigate these excitations, by either avoiding valley excitations or mitigating their impact, providing recipes for high-fidelity spin shuttling in several device regimes.
- Host: Mark Friesen; Susan Coppersmith
- Physics Department Colloquium
- No nus is good news
- Time: 3:30 pm - 4:30 pm
- Place: 2241 Chamberlin Hall
- Speaker: Daniel Green, UC San Diego
- Abstract: Cosmic surveys offer a unique window into fundamental physics, particularly the physics of light particles such as neutrinos. The recent results from DESI have placed surprisingly stringent constraints on the sum of neutrino masses, nearly excluding the entire range of masses consistent with neutrino oscillation measurements. In this colloquium, I will review what we have learned about cosmic neutrinos from maps of the universe. I will the discuss this confusing situation, the status possible explanations for the current data, and the implications for Beyond the Standard Model physics.
- Host: Moritz Münchmeyer, Gary Shiu
- Black and Brown in Physics
- Gender Minorities and Women in Physics
- BBiP & GMaWiP LGBTQ+ Heritage Month Movie Night
- Time: 5:30 pm - 7:30 pm
- Place: Chamberlain 2241
- Abstract: The Black and Brown in Physics (BBiP), and Gender Minorities and Women in Physics (GMaWiP) student orgs would like to invite you to our combined LGBTQ+ Heritage Month movie night happening Friday Oct. 25 at 5:30 PM in Chamberlain 2241. In honor of it also being October, we plan on showing the movie “I Saw the TV Glow”, a psychological horror film. We will also be providing popcorn and drinks! We hope that you will be able to join us! Important Note: This movie has a trigger warning for suicide ideation / imagery. Official Trailer: Synopsis: A classmate introduces teenage Owen to a mysterious late-night TV show -- a vision of a supernatural world beneath their own. In the pale glow of the television, Owen's view of reality begins to crack.
- Host: Faizah Siddique