  We develop a quasi-classical theory of high harmonic generation in
semiconductors based on an interband current that has been transformed from
Bloch to Wannier basis. The Wannier quasi-classical approach reveals a complete
picture of the mechanisms shaping high harmonic generation, such that
quantitative agreement with full quantum calculations is obtained. The
intuitive picture revealed by quasi-classical wavepacket propagation will be
helpful in the interpretation and design of high harmonic and attosecond
experiments. Beyond that, the capacity to quantitatively model quantum dynamics
with classical trajectories should prove useful for a wider spectrum of
condensed matter research, including coherent control, transport theory, and
strong field physics.
