Elastic strain engineering for ultralow mechanical dissipation
Sergey A. Fedorov1, Amir H. Ghadimi1, Nils Johan Engelsen1, Mohammad J. Bereyhi1, Dalziel Wilson2, Tobias Kippenberg1
1École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland
2 IBM Research Zürich, Rüschlikon, Switzerland
Nano- and micromechanical oscillators are indispensable for navigation, timing, motion sensing and wireless communication. In the past decade, a technological and scientific revolution has enabled quantum control of such NEMS and MEMS devices through electro- and opto- mechanical coupling. The major challenge to observing quantum effects is thermomechanical noise, which is typically reduced by operating in a cryogenic environment with high quality factor mechanical resonators. The pursuit of resonators with ultra-low dissipation has led to intense study of “dissipation dilution” by strain—a technique in which the stiffness of a mechanical oscillator made of high-strain material is effectively increased without added loss. This paradigm has to date relied on strain produced during material synthesis—the use of geometric strain engineering, capable of producing local strains near the material yield strength, remains largely unexplored. We show that geometric strain combined with a phononic crystal pattern can produce exceptionally high Q nanobeam mechanical resonators, possessing picogram-mass flexural modes with room-temperature Q factors as high as 800 million and Qf products of 1015 Hz—both unprecedented for a mechanical oscillator of any size. Additionally, stress-engineering allows us to tune the phononic bandgap across a wide range of frequencies while retaining Qf products above 1014 Hz. The devices we study can have force sensitivities of and at the same time perform hundreds of oscillations within their thermal decoherence time at room temperature, which make them attractive for use in cavity quantum optomechanics.