  We study novel types of contributions to the partition function of the
Maxwell system defined on a small compact manifold. These contributions, often
not addressed in the perturbative treatment with physical photons, emerge as a
result of tunneling transitions between topologically distinct but physically
identical vacuum winding states. These new terms give an extra contribution to
the Casimir pressure, yet to be measured. We argue that this effect is highly
sensitive to a small external electric field, which should be contrasted with
the conventional Casimir effect where the vacuum photons are essentially
unaffected by any external field. Furthermore, photons will be emitted from the
vacuum in response to a time-dependent electric field, similar to the dynamical
Casimir effect in which real particles are radiated from the vacuum due to the
time-dependent boundary conditions. We also propose an experimental setup using
a quantum LC circuit to detect this novel effect. We expect physical electric
charges to appear on the capacitor plates when the system dimension is such
that coherent Aharonov-Bohm phases can be maintained over macroscopically large
distances.
