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 Eötvös parameter with 95%-confidence to ${\eta }_{\text{Nb*-Cu}}\le 2.0\times {10}^{-9}$ and ${\eta }_{\text{CP-ee}}\le 9.2\times {10}^{-4}$ for superconducting niobium and Cooper pairs, respectively.