  When an atom or molecule absorbs a high-energy photon, an electron is emitted
with a well-defined energy and a highly-symmetric angular distribution, ruled
by energy quantization and parity conservation. These rules seemingly break
down when small quantum systems are exposed to short and intense light pulses,
which raise the question of their universality for the simplest case of the
photoelectric effect. Here we investigate the photoionization of helium by a
sequence of attosecond pulses in the presence of a weak infrared dressing
field. We continuously control the energy and introduce an asymmetry in the
emission direction of the photoelectrons, thus contradicting well established
quantum-mechanical predictions. This control is possible due to an extreme
temporal confinement of the light-matter interaction. Our work extends
time-domain coherent control schemes to one of the fastest processes in nature,
the photoelectric effect.
