  We investigate the liberation of an atomic electron by a linearly polarized
single-cycle near-infrared laser pulse having a peak intensity that ensures
tunneling. Based on phase space analysis and energy distribution in the
instantaneous potential, we reveal the importance of quantum interference
between tunneling and over-the-barrier pathways of escape. Tunneling is blurred
both in space and time, and the contribution of tunneling at the mean energy is
almost negligible. We suggest and justify improved initial conditions for a
classical particle approximation of strong-field ionization, based on the
quantum momentum function, and we show how to reconstruct them from the
detected momentum of an escaped electron.
