Zeit, Ort:

11:15 Uhr, Otto Hahn lecture hall, library building

Redner:

Dr. Pei-Lun He, MPIK

Titel:

Photoelectron Polarization Vortexes in Strong-Field Ionization

Abstract: // The spin polarization of photoelectrons induced by an intense linearly polarized laser field is investigated using numerical solutions of the time-dependent Schrödinger equation in companion with our analytic treatment via the spin-resolved strong-field approximation and classical trajectory Monte Carlo simulations. We demonstrate that, even though the total polarization vanishes upon averaging over the photoelectron momentum, momentum-resolved spin polarization is significant, typically exhibiting a vortex structure relative to the laser polarization axis. The polarization arises from the transfer of spin-orbital coupling in the bound state to the spin-correlated quantum orbits in the continuum. The rescattering of photoelectrons at the atomic core plays an important role in forming the polarization vortex structure, while there is no significant effect of the spin-orbit coupling during the continuum dynamics. Furthermore, spin-polarized electron holography is demonstrated, feasible for extracting fine structural information about the atom.

Zeit, Ort:

11:15 Uhr, Grosser Hoersaal/Big Lecture Hall (library)

Redner:

Dr Christoph Wiesinger

Titel:

Probing the neutrino mass with KATRIN and ultra-low background X-ray detectors for IAXO

Our understanding of fundamental particles is incomplete. The absolute neutrino mass remains unknown and strong interactions appear suspiciously symmetric, hinting at the existence of axions. KATRIN performs precision spectroscopy of tritium beta-decay electrons, probing the effective electron anti-neutrino mass with unprecedented sensitivity. IAXO is a next-generation helioscope aiming to detect solar axions, as they are converted into X-rays along a strong magnet pointing towards the sun. In my presentation, I will discuss the challenging analysis of the first five KATRIN neutrino mass campaigns and the potential of ultra-low background semiconductor detectors, based on the TRISTAN upgrade of KATRIN, to boost the search for solar axions with IAXO.

Zeit, Ort:

11:15 Uhr, Otto Hahn lecture hall, library building

Redner:

Dr. Michael Quin, MPIK

Titel:

Electron-positron microbunches as a source of XUV attosecond light pulses

Zeit, Ort:

09:30 Uhr, Central Seminar Room, library building

Redner:

Nick Lackmann, Highly charged ion dynamics

Titel:

tba

Zeit, Ort:

11:15 Uhr, Central seminar room, library building

Redner:

Prof. Marcus Dahlström, Department of Physics, Lund University

Titel:

Playing with XUV-dressed atoms: Stabilization, entanglement, triplets, zero areas and other ideas from quantum optics

Free electron laser (FEL) sources can provide short-wavelength radiation with sufficient intensity to induce coherent nonperturbative electron dynamics in atoms. Rabi oscillations at extreme ultraviolet (XUV) wavelengths have been observed on ultrafast timescales for helium atoms using the seeded XUV-FEL at FERMI [1]. Interestingly, the nonlinear photoionization processes, from the ground state (1s2) and the resonant excited state (1s4p), resulted in a subtle quantum interference effect that caused strong asymmetries in the experimental signal. This effect opens up novel possibilities for quantum coherent control.Here, we propose that helium atoms, subjected to circularly polarized FEL pulses, can be used to study a previously unrealized effect: dressed-atom stabilization [2]. The signature of this effect is found in the photoelectron distribution of a Rabi cycling atom: as a single photoelectron peak, rather than the expected doublet peaks (Autler-Townes effect) that are usually associated with the two dressed states.Further, we present an analysis of the time-dependent von Neumann entropy of entanglement in a related process: One photon XUV ionization, followed by XUV dressing of the ion [3]. Comparison is made with recent XUV-FEL experiments performed at FERMI for the reaction: 1s2 > 1sEp <> 2pEp in helium atoms. We show how the emerging doublet structure in the photoelectron distribution is related to the generation of quantum entanglement between the free photoelectron and the XUV-dressed ion. References:[1] Nandi, S. et al. Observation of Rabi dynamics with a short-wavelength free-electron laser. Nature 608, 488-493 (2022). https://doi.org/10.1038/s41586-022-04948-y [2] Olofsson, E. & Dahlström, J. M. Photoelectron signature of dressed-atom stabilization in an intense XUV field. Phys. Rev. Research 5, 043017 (2023).https://doi-org.ludwig.lub.lu.se/10.1103/PhysRevResearch.5.043017 [3] Nandi, S. et al. Generation of entanglement using a short-wavelength seeded free-electron laser. Sci. Adv. 10, eado0668 (2024).https://doi.org/10.1126/sciadv.ado0668 [4] Stenquist, A. et al. Mollow-like triplets in ultra-fast resonant absorption (preprint 2024)https://doi.org/10.48550/arXiv.2403.18676

Zeit, Ort:

11:15 Uhr, Seminar room Lindner 339, Gentner lab, 2nd floor

Redner:

Dr. Junichiro Kawamura (Institute for Basic Science, Daejeon, South Korea)

Titel:

Pseudo NG bosons from finite modular symmetry and radiative stabilization

In this talk, I argue that the modulus field of the finite modular symmetry can be stabilizedby the Coleman-Weinberg (CW) potential due to a modulus coupling to a heavy mass term,such as the vector-like quark masses in the KSVZ axion modeland Majorana mass of the type-I seesaw mechanism for the light neutrinos.As a result of this stabilization, the modulus is stabilized at a pointwhere the residual ZN symmetry is approximately unbroken.Interestingly, this ZN symmetry has an accidental U(1) symmetry,and thus the axionic component of the modulus becomes a pseudo NG boson. I will show two simple scenarios which are mostly the KSVZ axion and type-I seesaw models.For the former, I will discuss its consequence to the strong CP problem,and the majoron contributions to dark matter and radiation in the latter scenario.The study for the axion model can be found in arXiv:2402.02071.