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

Abstract

Exposed to a strong electromagnetic field, a two-level system with broken inversion symmetry radiates at the Rabi frequency ΩR. 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 $sqrt{(xi_1-xi_2)^2+Omega_R^2}$, where energies ℏξ1 and ℏξ2 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 $sqrt{(xi_1-xi_2)^2+Omega_R^2}$ is suppressed.