  The phase of the wave function of charged matter is sensitive to the value of
the electric potential, even when the matter never enters any region with
non-vanishing electromagnetic fields. Despite its fundamental character, this
archetypal electric Aharonov-Bohm effect has evidently never been observed. We
propose an experiment to detect the electric potential through its coupling to
the superconducting order parameter. A potential difference between two
superconductors will induce a relative phase shift that is observable via the
DC Josephson effect even when no electromagnetic fields ever act on the
superconductors, and even if the potential difference is later reduced to zero.
This is a type of electromagnetic memory effect, and would directly demonstrate
the physical significance of the electric potential.
