  Photon is a concept that does not apply at the instantaneous level when light
is described by classical electromagnetic fields. Exploiting the dynamical
rotational symmetry of circularly or elliptically polarized classical light
pulses, however, we demonstrate the existence of instantaneous quasiphotons
down to the subcycle level. We illustrate the concept of quasiphotons in
strong-field ionization through the correlated spectrum of angular momentum and
energy of photoelectrons, both at the tunnel exit and in the asymptotic region.
Moreover, we propose a protocol based on electron vortices to directly
visualize the existence of quasiphotons. Our work paves the pathway towards a
deeper understanding of fundamental light-matter interactions with photonic
characteristics on the subcycle scale.
