Winter semester 2024/2025
Organiser: Uwe Bandelow
Research seminar "Mathematical Models of Photonics"
Enrollment to the seminar: Students who want to attend this seminar for the modules P27, P28 and P35.3 should write an email to uwe.bandelow@hu-berlin.de. Please write as subject MathPho, your name, enrollment number, course of study.
I will save the email address and use it to send information regarding the seminar if this is not explicitly objected. You can cancel your enrollment to the seminar via email as well.
Proposed seminars
Thursday 21.11.2024, 14:00 (WIAS R405-406)Yusuke Kato. University of TokyoThursday 21.11.2024, 15:00 (WIAS R405-406)
Introduction of two studies: (1) analysis of oscillation quenching by periodic perturbation and (2) parameter estimation of Kuramoto model
I will talk about the two different projects that I am working on in Japan. (1) In the first part, I will present the oscillation quenching (annihilation of oscillation) in a bistable oscillator model [1]. We find that multiplicative periodic forces combined with feedback induce quenching and perform the bifurcation analysis using an averaging approximation. (2) The second part would be about the parameter estimation of the Kuramoto model, which is a mathematical model that describes synchronization phenomena. We use the time series of the order parameter (a macroscopic quantity that characterizes how the whole population is synchronized) as given data and estimate the model parameters. The estimation is performed by the Bayesian approach, using the exchange Monte Carlo method for computation.
[1] Y. Kato and H. Kori. Periodic forces combined with feedback induce quenching in a bistable oscillator. Chaos 34, 103125 (2024).
Hidemasa Ishii . University of TokyoWednesday 05.03.2025, 13:00 (HVP11a Videoconference room)
Employing dynamical modeling to understand complex phenomena: from interacting bistable systems to football ball possession
In this seminar, I would like to introduce two projects I have worked on. The first is a study on diffusively coupled stochastic bistable elements [1], where we analysed the influence of coupling strength over the mean escape time. Direct numerical simulations suggested, while strong coupling impedes escape, weak coupling facilitates escape on average. We argue, although diffusive coupling both facilitates and impedes escape, the facilitating effect is dominant under weak coupling. The second topic concerns dynamical modelling for three-versus-one ball possession in football. In our model, motion of the players and ball is governed by a system of ODEs during a single pass. The model is nevertheless stochastic, because the initial condition and parameters of the ODEs depend probabilistically on the final state of the previous pass. We aim to utilize this approach to quantify the difference between high- and lower-level football teams.
[1] H. Ishii and H. Kori, Diffusive coupling facilitates and impedes noise-induced escape in interacting bistable elements, Sci Rep 14, 11019 (2024).
Abel Thayil, WIAS BerlinWednesday 05.03.2025, 13:30 (HVP11a Videoconference room)
Optimization of valley splitting in Si/SiGe spin-qubits
Silicon-germanium (SiGe) heterostructures are a major candidate for realizing fully scalable quantum computers due to their inherently long spin coherence times and compatibility with existing semiconductor fabrication techniques. A critical challenge in strained Si/SiGe quantum wells is the existence of two nearly degenerate conduction band minima that can lead to leakage of quantum information. In the literature, several strategies have been proposed to enhance the energy splitting between the two valleys such as sharp interfaces [1], oscillating Ge-concentrations (wiggle well) [2] and shear strain engineering [3]. In this work, we formulate the design of the epitaxial profile in the quantum well as a constrained optimization problem and seek an optimized alloy composition profile that maximizes the valley splitting while respecting several manufacturing limitations. Our approach is based on coupled envelope equations combined with empirical pseudopotential theory to incorporate effects of disorder and strain in SiGe alloys. We demonstrate that our approach reproduces existing heuristics such as the wiggle well and the Germanium spike as limiting cases but also finds enhanced epitaxial profiles. Our work thus represents a valuable design tool for Si/SiGe heterostructures to further improve the valley splitting beyond the current state of the art.
[1] Losert et al. Phys. Rev. B 108.12 (2023)
[2] McJunkin et al. Nat. Commun 13, 7777 (2022)
[3] Woods et al. Npj Quantum Inf. 10, 54 (2024)
Lasse Ermoneit, WIAS Berlin
Optimal control for coherent electron shuttling of a SiGe-quantum bus in the presence of charged defects