Constraints on Axionlike Dark Matter with Masses Down to 10^{-23}  eV/c^{2}.
We analyzed a 6.7-yr span of data from a rotating torsion-pendulum containing ≈10^{23} polarized electrons to search for the "wind" arising from ultralight, axionlike dark matter with masses between 10^{-23} and 10^{-18}  eV/c^{2}. Over much of this range we set a 95% confidence limit F_{a}/C_{e}>2×10^{15}  eV on the axionlike decay constant.