  Semiconductor quantum dots (QDs) in photonic nanocavities provide monolithic,
robust platforms for both quantum information processing and cavity quantum
electrodynamics (QED). An inherent feature of such solid-state cavity QED
systems is the presence of electron-phonon interactions, which distinguishes
these systems from conventional atomic cavity QED. Understanding the effects of
electron-phonon interactions on these systems is indispensable for controlling
and exploiting the rich physics that they exhibit. Here we investigate the
effects of electron-phonon interactions on a QD-based cavity QED system. When
the QD and the cavity are off-resonance, we observe phonon-assisted cavity mode
emission that strongly depends on the temperature and cavity-detuning. When
they are on-resonance, we observe an asymmetric vacuum Rabi doublet, the
splitting of which narrows with increasing temperature. These experimental
observations can be well reproduced using a cavity QED model that includes
electron-acoustic-phonon interactions. Our work provides significant insight
into the important but hitherto poorly understood mechanism of non-resonant
QD-cavity coupling and into the physics of various cavity QED systems utilizing
emitters coupled to phonons, such as nitrogen-vacancy centres in diamond and
colloidal nanocrystals.
