  We investigate a singly-charged quantum dot under a strong optical driving
field by probing the system with a weak optical field. When the driving field
is detuned from the trion transition, the probe absorption spectrum is shifted
from the trion resonance as a consequence of the dynamic Stark effect.
Simultaneously, a gain sideband is created, resulting from the coherent energy
transfer between the optical fields through the quantum dot nonlinearity. As
the pump detuning is moved from red to blue, we map out the anticrossing of
these two spectral lines. The optical Bloch equations for a stationary
two-level atom can be used to describe the numerous spectral features seen in
this nano solid state system.
