  A novel search technique for ultralight dark matter has been developed and
carried out over a narrow range in L band, utilizing the recent Breakthrough
Listen public data release of three years of observation with the Green Bank
Telescope. The search concept depends only on the assumption of decay or
annihilation of virialized dark matter to a quasimonochromatic radio line, and
additionally that the frequency and intensity of the line be consistent with
most general properties expected of the phase space of our Milky Way halo.
Specifically, the search selects for a line that exhibits a Doppler shift with
position according to the solar motion through a static Galactic halo, and
similarly varies in intensity with the position with respect to the Galactic
center. Over the frequency range $1.73-1.83$ GHz, radiative annihilation of
dark matter is excluded above $\langle{\sigma}v\rangle$ = $1.2 \times 10^{-47}
\text{ cm}^3 \text{ s}^{-1}$, and for decay above ${\lambda}$ = $4.1 \times
10^{-35} \text{ s}^{-1}$. The analysis of the full Breakthrough Listen GBT
dataset by this method ($25,000$ spectra, $1.1-11.6$ GHz) is currently
underway.
