  Quantum breathers are studied numerically in several electron-phonon coupled
finite chain systems, in which the coupling results in intrinsic nonlinearity
but with varying degrees of nonadiabaticity. As for quantum nonlinear lattice
systems, we find that quantum breathers can exist as eigenstates of the system
Hamiltonians. Optical responses are calculated as signatures of these coherent
nonlinear excitations. We propose a new type of quantum nonlinear excitation,
breather-excitons, which are bound states of breathers and excitons, whose
properties are clarified with a minimal exciton-phonon model.
