  In strong-field physics and attosecond science, intense light induces
ultrafast electron dynamics. Such ultrafast dynamics of electrons in matter is
at the core of phenomena such as high harmonic generation (HHG), where these
dynamics lead to emission of extreme UV bursts with attosecond duration. So
far, all ultrafast dynamics of matter were understood to originate purely from
the classical vector potential of the driving light, disregarding the influence
of the quantum nature of light. Here we show that dynamics of matter driven by
bright (intense) light significantly depend on the quantum state of the driving
light, which induces an effective photon-statistics force. To provide a unified
framework for the analysis & control over such a force, we extend the
strong-field approximation (SFA) theory to account for non-classical driving
light. Our quantum SFA (qSFA) theory shows that in HHG, experimentally feasible
squeezing of the driving light can shift & shape electronic trajectories and
attosecond pulses at the scale of hundreds of attoseconds. Our work presents a
new degree-of-freedom for attosecond spectroscopy, by relying on nonclassical
electromagnetic fields, and more generally, introduces a direct connection
between attosecond science and quantum optics.
