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Events on Tuesday, April 30th, 2024

Preliminary Exam
Modeling Solar Neutrino Flavor Evolution with Data Assimilation
Time: 11:00 am - 1:00 pm
Place: 5280 Chamberlin;
Speaker: Caroline Laber-Smith
Abstract: This talk will cover the application of statistical data assimilation (SDA) techniques to solar neutrinos in two cases. Statistical data assimilation is an inference method that incorporates system dynamics from theory to supplement sparse measurements. Solutions are found by minimizing deviation from both measurements and model dynamics and tested based on their predicted results outside of the measured region. We used this technique to model neutrino flavor evolution throughout the sun, starting from pure electron flavor at the center and undergoing Mikheyev-Smirnov-Wolfenstein (MSW) resonance as it travels outwards.

This is the first application of SDA to solar neutrinos using real data - measurements of Boron-8 solar neutrino flavor recorded by the Borexino and Sudbury Neutrino Observation (SNO) experiments were used to constrain neutrino flavor towards the edge of the sun. In the first case, we used this data as a test of the technique. We performed this optimization procedure with multiple energy bins matching the observations from the Borexino and SNO experiments separately. With both sets of measurements, we found that incorporating MSW resonance into the flavor evolution dynamics produces results consistent with the observations.

In the second case, we introduced parameter estimation by allowing the procedure to vary the matter potential inside the sun. As a test of adiabaticity, we used two different monotonically decreasing models of the matter potential as a function of radius. For each model, the potential was held fixed at the edge of our zone of inference to match the standard solar model, while the value at the core of the sun was used as a varying parameter. For both models, we found that a core potential between 0.025 and 0.030 per kilometer produces results most consistent with observed neutrino fluxes.
Host: Baha Balantekin
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Wisconsin Quantum Institute Seminar
Nano-Photonic Emitters for the “Quantum Age”: where imperfections lead to opportunities
Time: 3:30 pm - 5:00 pm
Place: Discovery Building, DeLuca Forum
Speaker: Evelyn Hu, Harvard University

Although we usually assume that a "perfect" material is required to produce the best emitters for nano-optical devices, defect states in wide bandgap semiconductors are defining a new frontier for quantum information technologies, offering correlated spin-photon information. Numerous materials platforms have been explored, including single crystal diamond, SiC and Si: ultimately these defect qubits will need to satisfy quantum systems-level requirements for coherence, brightness, and equivalence of states.

This talk will introduce some building-block devices for the evaluation of candidate defect qubits, with a focus on Silicon Vacancies in 4H-SiC. Nanobeam photonic crystal cavities serve as both exquisitely sensitive optical amplifiers [1], as well as "nanoscopes" that allow us to better understand the local environment of the silicon vacancies, interactions with proximal defects and pathways to better processing and control of the defects [2].

Forming defects directly into cavities by "Laser Writing" allows more rapid feedback of optimal defect formation conditions [3]. Embedding G-center defects in Si, within PN diodes allows a dynamic assessment of processing conditions and fine-tuning of defect properties [4]. In aggregate, these techniques help to build the foundational understanding to take defect qubits to the “next steps” in implementing new quantum information technologies.

[1] Bracher, David O., Xingyu Zhang, and Evelyn L. Hu. "Selective Purcell enhancement of two closely linked zero-phonon transitions of a silicon carbide color center." Proceedings of the National Academy of Sciences 114.16 (2017): 4060-4065.
[2] Gadalla, Mena N., Andrew S. Greenspon, Rodrick Kuate Defo, Xingyu Zhang, and Evelyn L. Hu. "Enhanced cavity coupling to silicon vacancies in 4H silicon carbide using laser irradiation and thermal annealing." Proceedings of the National Academy of Sciences 118, no. 12 (2021): e2021768118.
[3] Day, Aaron M., Jonathan R. Dietz, Madison Sutula, Matthew Yeh, and Evelyn L. Hu. "Laser writing of spin defects in nanophotonic cavities." Nature Materials (2023): 1-7.
[4] Day, Aaron M., Madison Sutula, Jonathan R. Dietz, Alexander Raun, Denis D. Sukachev, Mihir K. Bhaskar, and Evelyn L. Hu. "Electrical Manipulation of Telecom Color Centers in Silicon." arXiv preprint arXiv:2311.08276 (2023).

This event starts at 3:30pm with refreshments, followed at 3:45pm by a short presentation by Chengyu Fang (Mikhail Kats group), titled “Scalable passive optical masks that enable one- and two-species atom-trap arrays”. The invited presentation starts at 4pm.

Host: Mikhail Kats
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