In a recent issue of Nature Communications , strong indirect coupling between mechanical resonators in a graphene-based electromechanical system has been reported, which paved the way to all-mechanical long-distance communications. This experiment is a collaboration between the group of Prof. Guo-Ping Guo at USTC and Prof. Lin Tian at UC Merced.
Mechanical resonators provide a promising platform for the storage and manipulation of quantum and classical information. To transfer information between distant mechanical modes, an interface between these modes is needed . In the past, direct coupling between mechanical modes in a single mechanical resonator or between neighboring mechanical resonators has been observed. But the realization of indirect coupling between spatially-separated mechanical modes is an experimental challenge.
In this work , a graphene ribbon is suspended over three trenches between four metal electrodes, which defines three distinct electromechanical resonators. The central resonator is utilized as a phonon cavity that connects the two mechanical resonators at the ends. The phonon cavity mediates an effective coupling between the two end resonators through virtual excitations in a Raman-like process. By controlling the resonant frequency of the phonon cavity, the indirect coupling can be tuned in a wide range. This result can lead to the development of gate-controlled all-mechanical devices and open up the possibility of long-distance quantum mechanical experiments in near future.
 G. Luo, Z.-Z. Zhang, G.-W. Deng, H.-O. Li, G. Cao, M. Xiao, G.-C. Guo, L. Tian, and G.-P. Guo, Strong indirect coupling between graphene-based mechanical resonators via a phonon cavity, Nature Commun. 9, 383 (2018) . https://www.nature.com/articles/s41467-018-02854-4
 L. Tian, Optoelectromechanical transducer: reversible conversion between microwave and optical photons, Ann. Phys. (Berlin) 527, 1 (2015).