Test of the Equivalence Principle for Superconductors

Abstract

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 $\eta_{\text{Nb*-Cu}}~\leq~2.0\times10^{-9}$ and $\eta_{\text{CP-ee}}\leq9.2\times10^{-4}$ for superconducting niobium and Cooper pairs, respectively.