Coherent Cavity Optomechanics in Wide-Band Gap Materials

Abstract

The utilization of photon-phonon interactions for transducing, storing, and transmitting information holds great promise for linking disparate quantum technologies. Cavity optomechanics aims to enhance coherent phonon-photon interactions through co–localization of mechanical and optical resonances coupled via radiation pressure or other optical forces. Many on-chip demonstrations of optomechanical cavities have relied on silicon-on-insulator as a material platform, which suffers from large nonlinear absorption at the telecommunication wavelengths widely used in optical communication technologies. The optomechanical cooperativity, C, which describes the efficiency of exchange between photons and phonons, is proportional to the intracavity photon number, N. As such, there is great interest in circumventing nonlinear absorption in these cavities, where the approach taken in this thesis is to use wide-band gap materials, which do not exhibit nonlinear absorption at these wavelengths. In this work, microdisk optomechanical cavities fabricated from gallium phosphide (GaP) and single-crystal diamond (SCD) were studied. The ability of these structures to support large N, while remaining thermally stable, enabled the demonstration of optomechanically induced self-oscillation and coherent processes such as optomechanically induced transparency and amplification with cooperativity C > 1. An advantage of microdisk cavities is that they support optical modes across the transparency window of the material, enabling the study of multimode optomechanics where multiple optical modes are coupled to the same mechanical mode of the microdisk. This resulted in the demonstration of optomechanically mediated wavelength conversion with internal conversion efficiency of 45 %. These cavities hold great potential for applications in quantum networks, namely as a phonon mediated transducer of quantum information from visible or microwave photons to telecommunication wavelength photons. SCD microdisk cavities also have potential application as a hybrid-quantum system which can couple electron spins from defect centers in the diamond lattice to telecommunications wavelength photons via phonons in the optomechanical cavity.