Sub-attonewton force detection in three dimensions with a single atom sensor

Ultra-sensitive force measurements are a crucial tool for investigating fundamental physical limits. Here we demonstrate a sub-attonewton force sensor based on a single trapped ion that can resolve all three dimensions components of an applied force through super-resolution imaging. The force is detected by measuring the ion displacement with nanometer precision with a sensitivity of 372$+$/-9 zN/$\surd $Hz in one direction, and (335, 359) $+$/-14 zN/$\surd $Hz and (779, 836)$+$/-42 zN/$\surd $Hz for the other two axes. After characterizing our system in all three dimensions, we demonstrated its accuracy by measuring a light pressure force on the ion of 95 zN.