Giessen works on ultrafast nano-optics and plasmonics, plasmonic and metasurface sensors, femtosecond two-photon 3D-printed micro-optics (on fiber tips and detectors), widely tunable ultrafast/mid-IR sources for molecular sensing, and Rydberg-exciton quantum optics in cuprous oxide. In the broader landscape of NV-centre ensemble quantum sensing (DEER, nano-NMR, T1 relaxometry) operating near pT/sqrt(Hz) sensitivity, this work sits adjacent as a nanophotonic sensing and light-source enabler.

Main works on nonlinear dynamics, semiclassics and quantum chaos, and is the principal theorist behind Stuttgart's Rydberg-exciton programme: high-n excitons in cuprous oxide, where the giant excitonic Rydberg states show magnetoexciton spectra, level statistics and symmetry breaking that his group models quantitatively. This is the theoretical partner to Giessen's (existing PI) experimental Rydberg-exciton work. Relative to the established NV-ensemble quantum-sensing playbook (DEER, nanoscale NMR, T1 relaxometry at pT/sqrt(Hz) ensemble sensitivity), a borderline theory inclusion, kept because Rydberg excitons are a genuinely promising solid-state electrometry platform -- giant polarizability in a semiconductor rather than a vapour cell -- and this is the group that understands their spectra.