  A model is discussed in which an electric field induces quantum nucleation of
soliton-antisoliton pairs in a pinned charge or spin density wave. Coulomb
blockade prevents pair creation until the electric field exceeds a sharp
threshold value, which can be much smaller than the classical depinning field.
We calculate the vacuum state energy and expectation value of the phase, which
is treated as a quantum scalar field. We find that the phase can also be much
smaller, below threshold, than predicted by classical ``sliding'' density wave
models.
