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 Schrödinger cat-like fields with frequencies distinct from those of the applied lasers.Many scientific and technological advances during the last decades, across diverse areas of human knowledge, can be associated to the manipulation of light-matter interaction and the generation of light fields in particular. One such achievement is the laser [1]. Here a photon stimulates an atom to decay into the ground state at the expense of the emission of another photon. To amplify this process, the emitting medium (atoms) is placed inside an optical resonator where the repeated reflection of the light allows for a sufficiently strong coupling between the atoms and the field [2]. By decreasing the volume of the optical resonator it is possible to reach a regime where a single atom and a single photon interact strongly, forming an atom-photon molecule. This establishes the research field known as cavity quantum electrodynamics (cavity QED) [3][4][5][6][7][8][9] where the atom-light interaction is controlled at its most fundamental level. Integrating the phenomenon of electromagnetically induced transparency (EIT) [10-12] adds additional capabilities such as allowing an opaque cavity QED system to become transparent [13][14][15][16]. The origin of this effect lies in the destructive interference of different absorption paths, preventing light from being absorbed by the system. We exploit this situation with a three-level atom in a Λ-type level configuration (one excited and two ground states) where one branch is strongly coupled to a mode of an optical resonator and the other to an external laser. In the EIT regime, the system remains in a state known as a dark state, since the atom does not absorb light from the fields.Here we show that this scheme can be used to continuously generate light that is genuinely quantum in nature. To this end, we introduce a second laser field which couples the two ground states. As expected for several waves interacting with a nonlinear medium, this gives rise to a new radiation field via an optical wave mixing process [17][18][19][20][21]. Not expected, however, is that if the laser field coupling the atomic ground states is weak enough, the fragile dark states of the cavity EIT system are not destroyed, even when all fields are on resonance with the respective atomic transitions. We then find that the two lasers in combination with the cavity drive transitions between dark states that differ by one photon in the cavity. Thus, the atomic excitation is suppressed due to the destructive interference of the EI...