  Chip-based cavity quantum electrodynamics (QED) devices consisting of a
self-assembled InAs quantum dot (QD) coupled to a high quality factor GaAs
microdisk cavity are coherently probed through their optical channel using a
fiber taper waveguide. We highlight one particularly important aspect of this
all-fiber measurement setup, which is the accuracy to which the optical
coupling level and optical losses are known relative to typical free-space
excitation techniques. This allows for precise knowledge of the intracavity
photon number and measurement of absolute transmitted and reflected signals.
Resonant optical spectroscopy of the system under both weak and strong driving
conditions are presented, which when compared with a quantum master equation
model of the system allows for determination of the coherent coupling rate
between QD exciton and optical cavity mode, the different levels of elastic and
inelastic dephasing of the exciton state, and the position and orientation of
the QD within the cavity. Pump-probe measurements are also performed in which a
far off-resonant red-detuned control laser beam is introduced into the cavity.
Rather than producing a measurable ac-Stark shift in the exciton line of the
QD, we find that this control beam induces a saturation of the resonant system
response. The broad photoluminescence spectrum resulting from the presence of
the control beam in the cavity points to sub-bandgap absorption in the
semiconductor, and the resulting free-carrier generation, as the likely source
of system saturation.
