Two dimensional optomechanical crystals for quantum optomechanics

Cooling of nanomechanical resonators to their motional ground state [1, 2] triggered recent achievements like non-classical mechanical state preparation [3] or coherent optical to microwave photon conversion [4]. Implementations of such system with optomechanical crystal (OMC) resonators use the co-localization of optical and acoustic modes in a periodically patterned device layer of a silicon-on-insulator (SOI) chip. An initialization of mechanical resonator to low thermal occupations is required by most quantum optomechanical operations. Reaching small thermal mechanical mode occupations and mechanical Q-factors ≳ 10^6 requires pre-cooling to millikelvin temperatures, where even weak optical absorption induces unfavorable local heating [5]. Commonly used one-dimensional nanobeam OMC resonators have significantly smaller thermal connectivity to the cool environment and reduced robustness against undesired heating than their two-dimensional counterparts. On the other hand drawbacks of 2D OMCs were their complex fabrication and weaker interaction strengths of acoustic and optical modes [6]. Here, we present a modified 2D OMC cavity that both exhibits simulated coupling strengths comparable to the previous optomechanical nanobeams and reduces the complexity for nanofabrication compared to previous 2D OMCs