Cassidy's group performs precision optical and microwave spectroscopy of positronium -- a purely leptonic electron-positron atom -- to test bound-state QED to high order and search for new physics, most recently a precision microwave measurement of the 2^3S1 to 2^3P2 fine-structure interval. The group is also developing slow, focused positronium beams toward a laboratory measurement of antimatter's gravitational free-fall, continuing UCL's 50-year history of positron physics.

Walz works on precision spectroscopy of exotic atoms and antimatter. The group is known for continuous-wave Lyman-alpha (121.6 nm) laser sources -- the enabling technology for laser cooling of antihydrogen -- and for antihydrogen and positronium spectroscopy aimed at CPT tests and at antimatter gravity measurements, in collaboration with CERN antiproton-decelerator experiments. Complementary work at Mainz covers laser development, exotic-atom trapping and detection. Relative to the established NV-ensemble quantum-sensing playbook (DEER, nanoscale NMR, T1 relaxometry at pT/sqrt(Hz) ensemble sensitivity), this is a fundamental-symmetry pivot: the sensing content is in ultra-stable lasers, extreme-vacuum trapping and single-particle detection rather than solid-state spins, and it suits a postdoc looking to move from quantum sensors toward fundamental-physics tests.