  Adiabatic frequency shifting is demonstrated by tuning an ultrahigh-Q
photonic crystal nanocavity dynamically. By resolving the output temporally and
spectrally, we showed that the frequency of the light in the cavity follows the
cavity resonance shift and remains in a single mode throughout the process.
This confirmed unambiguously that the frequency shift results from the
adiabatic tuning. We have employed this process to achieve the dynamic release
of a trapped light from an ultrahigh-Q cavity and thus generate a short pulse.
This approach provides a simple way of tuning Q dynamically.
