  In a ring of s-wave superconducting material the magnetic flux is quantized
in units of $\Phi_0 = \frac{h}{2e}$. It is well known from the theory of
Josephson junctions that if the ring is interrupted with a piece of d-wave
material, then the flux is quantized in one-half of those units due to a
additional phase shift of $\pi$. We reinterpret this phenomenon in terms of
geometric phase.
  We consider an idealized hetero-junction superconductor with pure s-wave and
pure d-wave electron pairs. We find, for this idealized configuration, that the
phase shift of $\pi$ follows from the discontinuity in the geometric phase and
is thus a fundamental consequence of quantum mechanics.
