Gigahertz-frequency Lamb wave resonator cavities on suspended lithium niobate for quantum acoustics

TL;DR

This paper investigates gigahertz-frequency Lamb wave resonator cavities on suspended lithium niobate, demonstrating strong phonon confinement and high quality factors suitable for quantum acoustic applications.

Contribution

It introduces a new design of GHz Lamb wave resonator cavities on suspended lithium niobate with high quality factors at millikelvin temperatures.

Findings

Resonator cavities achieve Q-factors of about 6000 at the single phonon level.

Strong confinement of Lamb waves in 200 nm lithium niobate layer.

Potential for coupling to superconducting qubits demonstrated through modeling.

Abstract

Phononic nanodevices offer a promising route toward quantum technologies, as phonons combine strong confinement within matter with broad coupling capabilities to various quantum systems. In particular, the piezoelectric response of materials such as lithium niobate enables coupling between superconducting qubits and gigahertz-frequency phonons. However, bulk lithium niobate phononic devices typically rely on surface acoustic waves and are therefore inherently subject to leakage from the surface into the bulk substrate. Here, we explore the acoustic behavior of resonator cavities supporting GHz-frequency Lamb waves in a 200 nm-thick suspended lithium niobate layer. We characterize the acoustic response at both room and millikelvin temperatures. We find that our resonator cavities with strong confinement reach intrinsic quality factors of approximately 6000 at the single phonon level. We use the measured parameters of the resonators to model their coupling to a superconducting transmon qubit, allowing us to evaluate their potential as quantum acoustic devices.