ERIK MCLEAN / UNSPLASH

Physikalisches Kolloquium

Freitag, 25. April 2025 17:00 Uhr  Embracing uncertainty: a photonic approach to probabilistic computing

Prof. Dr. Wolfram Pernice, Kirchhoff-Institut für Physik, Universität Heidelberg

Unlike artificial neural networks (ANNs), which focus on maximizing accuracy, biological systems excel at handling uncertainty. This ability is believed to be essential for adaptability and efficiency, yet traditional ANNs, implemented on deterministic hardware, struggle with capturing the full probabilistic nature of inference. To address this limitation, Bayesian neural networks (BNNs) replace deterministic parameters with probability distributions, allowing us to distinguish between epistemic uncertainty (due to limited data) and aleatoric uncertainty (arising from noise). By incorporating Bayesian inference, BNNs enable uncertainty quantification and allow for out-of-distribution detection in cases of incomplete data. However, processing probabilistic models remains a challenge for conventional digital hardware, which relies on deterministic von Neumann architectures that separate memory from computation. In electronic crossbar arrays, memristors exhibit inherent stochasticity, making them suitable for probabilistic inference. Yet, sequential sampling and variability in memristive materials present obstacles.

To address these challenges, I will outline recent progress in photonic computing architectures that harness hardware noise as a computational resource rather than a constraint. Using nanoscale phase-change materials enables encoding and processing probabilistic information in an in-memory computing fashion. By transitioning to photonic crossbar arrays, we can achieve parallel probabilistic operations using chaotic light as a physical entropy source for random number generation. This approach paves the way for energy-efficient, high-speed probabilistic machine learning beyond the limitations of conventional hardware.

Teilchenkolloquium

A light approach to Dark Matter: the DELight experiment

Dr. Francesco Toschi, KIT, Karlsruhe

Astronomisches Kolloquium

Dienstag, 29. April 2025 16:30 Uhr  The build-up of galactic nuclei: how do black holes get there?

Nadine Neumayer, MPIA The centers of massive galaxies are special in many ways, not least because apparently all of them host supermassive black holes. Since the discovery of a number of relations linking the mass of this central black hole to the large scale properties of the surrounding galaxy bulge it has been suspected that the growth of the central black hole is intimately connected to the evolution of its host galaxy. However, at lower masses, and especially for bulgeless galaxies, the situation is much less clear. Interestingly, these galaxies often host massive star clusters at their centers, and unlike black holes, these nuclear star clusters provide a visible record of the accretion of stars and gas into the nucleus. I will present our ongoing observing programmes of the nearest nuclear star clusters, including the Milky Way Center, and the stripped galaxy nuclei Omega Centauri and M54 (still at the center of the Sagittarius dwarf galaxy). These observations provide important information on the formation mechanisms of nuclear star clusters, allow us to measure potential black hole masses and give clues on how black holes get to the centers of galaxies.

Zentrum für Quantendynamik Kolloquium

Donnerstag, 24. April 2025 11:15 Uhr  Magnetic soliton molecules in binary condensates

Rene Röhrs, BSc, Ultracold Quantum Matter Theory, University of Innsbruck