Low loss Bulk Acoustic Wave devices are considered from the point of view of the solid state approach as phonon-confining cavities. We demonstrate effective design of such acoustic cavities with phonon-trapping techniques exhibiting extremely high quality factors for trapped longitudinally-polarized phonons of various wavelengths. Quality factors of observed modes exceed 1 billion, with a maximum Q-factor of 8 billion and Q × f product of 1.6 · 1018 at liquid helium temperatures. Such high sensitivities allow analysis of intrinsic material losses in resonant phonon systems. Various mechanisms of phonon losses are discussed and estimated.
Galliou, S., Goryachev, M., Bourquin, R., Abbé, P., Aubry, J. P., & Tobar, M. (2013). Extremely low loss phonon-trapping cryogenic acoustic cavities for future physical experiments. Scientific Reports, 3, 6pp. https://doi.org/10.1038/srep02132