Test of the equivalence principle for superconductors

We searched for violations of the weak equivalence principle using a cryogenic torsion balance with a pendulum comprised of superconducting niobium and copper. We constrain the E\"otv\"os parameter with 95% confidence to ${\ensuremath{\eta}}_{{\mathrm{Nb}}^{*}\text{\ensuremath{-}}\mathrm{Cu}}\ensuremath{\le}2.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$ and ${\ensuremath{\eta}}_{\mathrm{CP}\text{\ensuremath{-}}\mathrm{ee}}\ensuremath{\le}9.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ for superconducting niobium and Cooper pairs, respectively.