Jean-Philippe Karr's trapped-ions group at LKB performs precision spectroscopy of molecular ions (HD+, H2+) to test quantum electrodynamics and determine fundamental constants. Research: (1) laser spectroscopy of HD+ molecular ions in ion traps for proton-electron mass ratio determination; (2) tests of quantum electrodynamics in simple molecular systems; (3) search for physics beyond the standard model via precision measurement. Published in Physics (April 2026) on simplest molecules testing quantum theory.