Events at Physics

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Events on Wednesday, December 21st, 2022

Academic Calendar
Final exams
Abstract: *Note: actual end time may vary.* URL:
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Preliminary Exam
Valley splitting and alloy disorder in Si/SiGe quantum dots
Time: 10:30 am - 12:30 pm
Place: Chamberlin 4274 or (passcode 630477)
Speaker: Merritt Losert, Physics Graduate Student
Abstract: Silicon/silicon-germanium heterostructures have many important advantages for hosting spin qubits. However, controlling the energy splitting between the two low-energy conduction-band valley states remains a critical challenge for scaling up to large numbers of reliable and reproducible qubits. Broad distributions of valley splittings are commonplace, even among quantum dots on the same device. Such behavior has previously been attributed to imperfections such as steps at the quantum well interface, which are known to strongly suppress the valley splitting. Many heterostructure designs have been proposed to boost the valley splitting, to overcome this problem. In this talk, we explore a simple, universal theory of valley splitting based on the reciprocal-space profile of the quantum-well confinement potential, which can explain the effects of steps, wide interfaces, alloy disorder, and custom heterostructure designs. We use this understanding to theoretically characterize the valley splitting in a variety of heterostructures, finding that alloy disorder causes substantial variations of the valley splitting, even in the absence of steps. Using this understanding, we lay out two approaches to engineer large valley splittings: one based on deterministically increasing the Fourier component of the quantum well potential that couples the valleys, and one that takes advantage of disorder to statistically increase the valley splitting.
Host: Mark Friesen
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Looking for new physics in rare and novel processes at the LHC
Time: 2:30 pm - 3:30 pm
Place: 4274 Chamberlin Hall & Zoom:
Speaker: Saptaparna Bhattacharya, Northwestern University
Abstract: The collection of a large dataset at the Large Hadron Collider (LHC) allows for the exploration of rare processes predicted by the Standard Model of Particle Physics. In this talk I will focus on the observation of triboson production with data collected by the CMS detector at a center of mass energy of 13 TeV using the complete Run II dataset. Triboson events are rare and feature novel topologies. I will provide a historical context for the first observation of tribosons at the LHC and discuss prospects for this analysis as we head toward Run III and the high luminosity-LHC. Given the absence of any significant sign of new physics at the LHC, an effective field theory (EFT) approach which posits that the source of new physics are heavy fields beyond our current reach, can be used to indirectly look for new physics. I will state how the newly observed triboson processes can be used as a probe for new physics using the EFT framework.
Host: Sridhara Dasu
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