  We present a proposal for a tunable source of single photons operating in the
terahertz (THz) regime. This scheme transforms incident visible photons into
quantum THz radiation by driving a single polar quantum emitter with an optical
laser, with its permanent dipole enabling dressed THz transitions enhanced by
the resonant coupling to a cavity. This mechanism offers optical tunability of
properties such as the frequency of the emission or its quantum statistics
(ranging from antibunching to entangled multi-photon states) by modifying the
intensity and frequency of the drive. We show that the implementation of this
proposal is feasible with state-of-the-art photonics technology.
