  We demonstrate the existence of a novel breather mode in the self-consistent
electron dynamics of a semiconductor quantum well. A non-perturbative
variational method based on quantum hydrodynamics is used to determine the
salient features of the electron breather mode. Numerical simulations of the
time-dependent Wigner-Poisson or Hartree equations are shown to be in excellent
agreement with our analytical results. For asymmetric quantum wells, a
signature of the breather mode is observed in the dipole response, which can be
detected by standard optical means.
