Two tunneling-coupled two-level systems with broken inversion symmetry: tuning the terahertz emission

Exposed to a strong electromagnetic field, a two-level system with broken inversion symmetry radiates at the Rabi frequency Omega(R). This can be used to generate terahertz waves [Phys. Rev. Lett. 102, 023601 (2009)]. We show that a system composed of two tunneling-coupled asymmetric two-level systems radiates at frequency root(xi(1) - xi(2))(2) + Omega(2)(R)), where energies (h) over bar xi(1) and (h) over bar xi(2) characterize the tunneling interaction. This opens the possibility of tuning the terahertz spectrum in a considerable range. We also show that for particular amplitudes of the driving field, the emission at frequency root(xi(1) - xi(2))(2) + Omega(2)(R)) is suppressed. (C) 2016 Optical Society of America