GoKawiilLu+ ion clock demonstrates frequency accuracy to 19th decimal place
Researchers reported an optical frequency reference using trapped lutetium ions (Lu+) whose accuracy was experimentally verified to the 19th digit. The system uses paired ion interrogation with Doppler cooling, a Ramsey-based HA–HR sequence, and active magnetic-field feedback via shim coils to suppress Zeeman shift drift, alongside auxiliary spectroscopy checks to keep the clock laser and field measurements calibrated.