Friday, 27. June 2025 5:00 pm  Melting of ice

Prof. Dr. Detlef Lohse , Max-Planck-Institut für Dynamik und Selbstorganisation, Göttingen und University of Twente

The quantitative understanding of glacial ice melting into the ocean is one of the most outstanding challenges in environmental fluid dynamics. The lack of understanding is on a fundamental level, due to the highly complex multi-scale, multi-physics nature of the problem. The process involves intricate multi- way coupling effects, including thermal convection, salinity, ocean current, and radiation, etc. As ice melts into the surrounding salty water, a decrease in local salt concentration leads to reduced water density, inducing upward buoyant forces and, consequently, upward flow. This flow dynamically interacts with the ice, resulting in a feedback loop of further melting (Stefan problem). Our investigation employs direct numerical simulations with the phase field method. To capture the intricacies of melting dynamics within turbulent flows, we implement a multiple-resolution strategy for salinity and phase field simulations [3]. The versatility of our method is demonstrated through successful applications to diverse melting scenarios, including the formation of melt ponds [2], melting in Rayleigh-Bénard convection [4], vertical convection with fresh water [1], and vertical convection with salty water [3]. In this presentation, we showcase results obtained across these various geometries. This work contributes to advancing our understanding of the complex dynamics involved in glacial ice melting within oceanic environments.

References

1. Rui Yang, Kai Leong Chong, Hao-Ran Liu, Roberto Verzicco, and Detlef Lohse. Abrupt transition from slow to fast melting of ice. Phys. Rev. Fluids, 7(8):083503, 2022.

2. Rui Yang, Christopher J. Howland, Hao-Ran Liu, Roberto Verzicco, and Detlef Lohse. Bistability in radiatively heated melt ponds. Phys. Rev. Lett., 131:234002, Dec 2023.

3. Rui Yang, Christopher J. Howland, Hao-Ran Liu, Roberto Verzicco, and Detlef Lohse. Ice melting in salty water: layering and non-monotonic dependence on the mean salinity. J. Fluid Mech., 969:R2, 2023.

4. Rui Yang, Christopher J Howland, Hao-Ran Liu, Roberto Verzicco, and Detlef Lohse. Morphology evolution of a melting solid layer above its melt heated from below. J. Fluid Mech., 956:A23, 2023.

The ALICE-3 upgrade plans

Dr. Kai Schweda, GSI GmbH, Darmstadt

Tuesday, 1. July 2025 4:30 pm  Unlocking the various evolutionary pathways of sun-like stars

Nicole Reindl , Heidelberg University (ZAH/LSW) There is no one way to live a life. How true this statement is also for stars is well reflected in the zoo of H-deficient stars, and strikingly beautiful and diverse planetary nebulae morphologies. In this talk, I will explore how late thermal pulses, stellar mergers, Type Ia supernovae, and magnetic fields can dramatically alter the observable characteristics of evolved stars. Understanding these processes helps us piece together the various evolutionary pathways that sun-like stars can follow.

Wednesday, 25. June 2025 4:30 pm  Coherent control of large nuclear spins in a degenerate Fermi gas of strontium

Dr. Martin Robert-de-Saint Vincent, Laboratoire de Physique des Lasers, Université Sorbonne Paris Nord Coherent control of large nuclear spins in a degenerate Fermi gas of strontium Martin Robert-de-Saint-Vincent Laboratoire de Physique des Lasers, Université Sorbonne Paris Nord Ultracold alkaline-earth atoms are used on a variety of platforms: quantum simulators, e.g. of generalised Fermi Hubbard models; neutral atom quantum computers; and high precision sensors such as optical atomic clocks. The spin degree of freedom of these atoms could be a powerful resource in the above applications. In this talk, I will discuss coherent manipulation schemes that enable harnessing it, i.e., provide the capability to prepare or measure any state. The spin of a ground-state strontium-87 atom has two key characteristics: it has a large quantum number F = 9/2, and it is entirely contained within the nucleus. This quantum number means that one atom could be in any of 10 states, or any quantum superposition of those. Consequently, one atom contains a lot of stored information, more than e.g. “qubits” that are in a superposition of two states. Furthermore, the nuclear nature of the spin gives these states strong robustness against environmental perturbations such that quantum superpositions can survive over many seconds. To manipulate or extract all that quantum information, one needs to be able to perform a set of several control operations. Spin precession around a magnetic field is one such operation, but is not sufficient. Here, we exploit a property of the atom called tensor polarisability to implement a sufficient set of distinct manipulations. We then realise proofof-principle experiments to illustrate opportunities offered by objects with large spin. Multiple fields can be measured in parallel, e.g. for noise cancellation in sensors; and a subset of states can serve as a primary resource (an effectively smaller spin), while the other states are used to perform seemingly incompatible quantum measurements in parallel. References: - P. Bataille et. al., Phys. Rev. A 102, 013317 (2020). - H. Ahmed et al, arxiv:2501.01731 (2025), to be published in PRX Quantum