Hengjiang Ren

Light is a powerful tool for controlling mechanical motion, as shown by numerous applications in the field of cavity optomechanics. Recently, small scale optomechanical circuits, connecting a few optical and mechanical modes, have been demonstrated in an ongoing push towards multi-mode on-chip optomechanical systems. An ambitious goal driving this trend is to produce topologically protected phonon transport. Once realized, this will unlock the full toolbox of optomechanics for investigations of topological phononics. Here, we report the realization of topological phonon transport in an optomechanical device. Our experiment is based on an innovative multiscale optomechanical crystal design and allows for site-resolved measurements in an array of more than 800 cavities. The sensitivity inherent in our optomechanical read-out allowed us to detect thermal fluctuations traveling along topological edge channels. This represents a major step forward in an ongoing effort to downscale mechanical topological systems.

Getting phonons to hang around: The ideal platform for quantum-computing and quantum-sensing applications is likely to be a hybrid system that combines the best features of different components. Superconducting circuits are relatively advanced, and finding components that can control and manipulate the microwaves will be essential. MacCabe et al. explored the use of high-quality microresonators in which the acoustic environment could be engineered such that the phonon lifetime could be extended to more than 1 second. Operating at microwave frequencies of 5 gigahertz, these quantum acoustic-dynamic devices could be coupled with superconducting circuits. Science , this issue p. 840

Summary form only given. 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.