Far-infrared frequency mode conversion using bulk acoustic phonon modes

The ability to design, fabricate and control systems which can convert photons with dissimilar frequencies has technological implications in classical as well as quantum communications. Laser heating and thermal mechanical motion in conventional micro/nanoscale optomechanical systems hamper the use of these systems in quantum information processing networks. In contrast, we propose an unconventional system comprising of a bulk quartz crystal placed within a Fabry-Pe'rot cavity. The pumping laser is in the far-infrared region. We explore the possibility of efficient mode conversion between two optical modes supported by the system, mediated by the bulk acoustic phonons of the quartz crystal. Unlike the earlier optomechanical systems, the dark mode in our proposed system is not decoupled from the mechanical mode and yet it enables the efficient mode conversion. The novel results found in our study can be used to harness the dark state for quantum state transfer. The proposed system is robust against excessive heating.