Temperature and power dependence of high-overtone transverse bulk acoustic modes in lithium niobate

Quantum acoustics systems in which superconducting qubits are coupled with the modes of a high-overtone bulk acoustic wave resonator (HBAR) are a promising platform for quantum computing, communications, and sensing. Recently, quasi-HBAR devices based on transverse bulk phonons in lithium niobate have been coupled to transmon qubits [1]. In this work, we report on the temperature and power dependence of these transverse bulk phonon modes, which can be excited via their free-space coupling to a three-dimensional microwave cavity. We find that the cavity response contains information regarding the spectral structure and loss of the HBAR device as well as the temperature and power dependent material properties of the lithium niobate substrate trapping the bulk phononic modes.

[1] J.M. Kitzman et al. Appl. Phys. Lett. 123, 224001 (2023)