Lithium niobate phononic crystal resonators show promise for quantum acoustic applications

Everyone who has heard a tuning fork ring down is familiar with the effects of loss in a mechanical resonator. As mechanical resonators are increasingly used in classical and quantum technologies, researchers have sought to better understand the sources of dissipation.

Wollack et. al investigate the losses in phononic crystal resonators made from lithium niobate, which use a phononic bandgap to eliminate losses due to mechanical waves propagating away. These nanoscale devices help provide a roadmap for the characterization of a wide class of quantum acoustic devices.

“Our analysis examines the phononic bandgap, electrodes, and materials loss channels to understand these fairly new electromechanical devices,” said author E. Alex Wollack.

When a mechanical oscillator is cooled down and researchers work at the smallest possible excitation levels, every defect in devices matter. Although the phononic crystal’s bandgap eliminates clamping losses, things like changes in the atomic structure of an imperfect crystal lattice can end up stealing energy from the mechanical resonator. For this reason, researchers focused on picking purer materials, like lithium niobate, and making design choices that mitigate the imperfections.

During initial testing, the researchers were surprised to find the devices were also well suited for mass detection. The fact that the mechanically active region is quite small, and the devices are easily frequency multiplexed make them ideal for mass-sensing applications.

“Lithium niobate is an extremely useful material for researchers to utilize in hybrid quantum devices due to its strong piezoelectricity and optical nonlinearity,” said Wollack. Consequently, lithium niobate is useful in applications in quantum circuits, transduction and networking.

Source: “Loss channels affecting lithium niobate phononic crystal resonators at cryogenic temperature,” by E. Alex Wollack, Agnetta Y. Cleland, Patricio Arrangoiz-Arriola Timothy P. McKenna, Rachel G. Gruenke, Rishi N. Patel, Wentao Jiang, Christopher J. Sarabalis, and Amir H. Safavi-Naeini, Applied Physics Letters (2021). The article can be accessed at https://doi.org/10.1063/5.0034909 .