  We have investigated the polarization response of a dielectric to intense
few-cycle laser pulses with a focus on interband tunnelling. Once charge
carriers are created in an initially empty conduction band, they make a
significant contribution to the polarization response. In particular, the
coherent superposition of conduction- and valence-band states results in
quantum beats. This quantum-beat part of the polarization response is affected
by the excitation dynamics and attosecond-scale motion of charge carriers in an
intense laser field. Our analysis shows that, with the onset of Bloch
oscillations or tunnelling, the nonlinear polarization response becomes
sensitive to the carrier-envelope phase of the laser pulse.
