  We show an optical wave-mixing scheme that generates quantum light by means
of a single three-level atom. The atom couples to an optical cavity and two
laser fields that together drive a cycling current within the atom. Weak
driving in combination with strong atom-cavity coupling induces transitions
between the dark states of the system, accompanied by single-photon emission
and suppression of atomic excitation by quantum interference. For strong
driving, the system can generate coherent or Schr\"odinger cat-like fields with
frequencies distinct from those of the applied lasers.
