  We investigate ionization of neon atoms by an isolated attosecond pump pulse
in the presence of two coherent extreme ultraviolet or x-ray probe fields. The
probe fields are tuned to a core-valence transition in the residual ion and
induce spectral shearing of the photoelectron distributions. We show that the
photoelectron-ion coincidence signal contains an interference pattern that
depends on the temporal structure of the attosecond pump pulse and the
stimulated core-valence transition. Many-body perturbation theory is used to
compute "atomic response times" for the processes and we find strikingly
different behavior for stimulation to the outer-core hole (2p - 2s) and
stimulation to the inner-core hole (2p - 1s). The response time of the
inner-core transition is found to be comparable to that of state-of-the-art
laser-based characterization techniques for attosecond pulses.
