  Superconducting nanowires, a mature technology originally developed for
quantum sensing, can be used as a target and sensor with which to search for
dark matter interactions with electrons. Here we report on a 180-hour
measurement of a tungsten silicide superconducting nanowire device with a mass
of 4.3 nanograms. We use this to place new constraints on dark matter--electron
interactions, including the strongest terrestrial constraints to date on
sub-MeV (sub-eV) dark matter that interacts with electrons via scattering
(absorption) processes.
