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arXiv · 1901.04129

Phononic bandgap nano-acoustic cavity with ultralong phonon lifetime

Gregory S. MacCabe·Hengjiang Ren·Jie Luo·Justin D. Cohen·Hengyun Zhou·Alp Sipahigil·Mohammad Mirhosseini·Oskar Painter
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Abstract

We present measurements at millikelvin temperatures of the microwave-frequency acoustic properties of a crystalline silicon nanobeam cavity incorporating a phononic bandgap clamping structure for acoustic confinement. Utilizing pulsed laser light to excite a co-localized optical mode of the nanobeam cavity, we measure the dynamics of cavity acoustic modes with single-phonon sensitivity. Energy ringdown measurements for the fundamental $5$~GHz acoustic mode of the cavity shows an exponential increase in phonon lifetime versus number of periods in the phononic bandgap shield, increasing up to $\tau \approx 1.5$~seconds. This ultralong lifetime, corresponding to an effective phonon propagation length of several kilometers, is found to be consistent with damping from non-resonant two-level system defects on the surface of the silicon device. Potential applications of these ultra-coherent nanoscale mechanical resonators range from tests of various collapse models of quantum mechanics to miniature quantum memory elements in hybrid superconducting quantum circuits.

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Gregory S. MacCabe, Hengjiang Ren, Jie Luo, Justin D. Cohen, Hengyun Zhou, Alp Sipahigil, Mohammad Mirhosseini, Oskar Painter. 2019-01-14. Phononic bandgap nano-acoustic cavity with ultralong phonon lifetime. https://doi.org/10.1126/science.abc7312

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