Constraints on axionlike dark matter with masses down to $10^{-23}$
  eV/c$^2$
  We analyzed an 6.7-year span of data from a rotating torsion-pendulum
containing $\approx 10^{23}$ 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 most of this range we obtain a 95\% confidence
limit $F_{\rm a}/C_{\rm e} \geq 1 \times 10^{15}$ eV on the axionlike decay
constant.
