The feasibility of generating correlated photon pairs at variable frequencies is investigated. For this purpose we consider the interaction of an off-resonant laser field with a two-level system possessing broken inversion symmetry. We show that the system generates nonclassical photon pairs exhibiting strong intensity-intensity correlations. The intensity of the applied laser tunes the degree of correlation while the detuning controls the frequency of one of the photons, which can be in the terahertz domain. Furthermore, we observe the violation of a Cauchy-Schwarz inequality characterizing these photons.

• Received 4 November 2011

DOI:https://doi.org/10.1103/PhysRevA.85.063814