  By developing a quantum virial expansion theory, we quantitatively calculate
the dynamic density response function of a trapped strongly interacting Fermi
gas at high temperatures near unitarity. A clear transition from atomic to
molecular responses is identified in the spectra when crossing from the BCS to
BEC regimes, in qualitative agreement with recent Bragg spectroscopy
observations. Our virial expansion method provides a promising way to solve the
challenging strong-coupling problems and is applicable to other dynamical
properties of strongly correlated Fermi gases.
