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.

Chantler's group is built around the idea that X-ray measurements can be made accurate, not just precise: the X-ray Extended Range Technique (XERT) delivers absolute absorption coefficients at the 0.02 per cent level, which in turn allows XAFS to be used for quantitative structure determination and allows high-accuracy tests of atomic theory. The second thread is precision X-ray spectroscopy of highly charged ions and exotic atoms as a test of bound-state QED, where discrepancies between theory and experiment remain unresolved. Positioned against the established body of NV-ensemble quantum sensing work — DEER, nanoscale NMR and T1 relaxometry protocols operating at pT/sqrt(Hz) field sensitivity — this is precision measurement at the other end of the electromagnetic spectrum: the methodological common ground with pT/sqrt(Hz) NV ensemble sensing is the obsessive treatment of systematics and absolute calibration that separates a sensitive measurement from an accurate one. Borderline inclusion, kept because the group's core competency is metrology rather than X-ray applications.

Pohl is the central figure in muonic-atom precision spectroscopy -- the measurements that produced the proton-radius puzzle. Replacing the electron with a muon shrinks the Bohr radius ~200x and amplifies sensitivity to nuclear structure by ~10^7, so laser and microwave spectroscopy of muonic hydrogen/deuterium/helium yields charge and magnetization radii at otherwise unreachable precision. Current pushes: the CREMA/HyperMu measurement of the proton's magnetic (Zemach) structure via the muonic-hydrogen hyperfine splitting, and QUARTET, targeting ~10x better charge radii for light nuclei from Li to Ne. Work is done at PSI with cryogenic targets, ultrafast trigger lasers and X-ray detector arrays. Relative to the established NV-ensemble quantum-sensing playbook (DEER, nanoscale NMR, T1 relaxometry at pT/sqrt(Hz) ensemble sensitivity), this is a different sensing regime entirely -- the 'sensor' is the atom and the challenge is systematics at the 10^-5 level -- but it is a strong pivot for a postdoc who wants extreme metrology and detector work rather than condensed-matter spin 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.