Coherence studies of hundreds of overtone modes in a bulk acoustic wave resonator

High overtone bulk acoustic wave resonators (HBAR) have been successfully integrated with superconducting (SC) qubits into hybrid quantum systems that have many applications in quantum information technologies [1]. The coherences of HBAR modes have been extensively studied in relation to surface roughness, defect density, and other material properties [2]. However, the full multimode spectrum of HBARs in hybrid quantum systems has not yet been understood and characterised.



Here, we present a study of the coherence properties of hundreds of HBAR modes spanning several-GHz in frequency. Using a microwave antenna that is designed to electro-mechanically couple primarily to the Lagueurre-Gaussian (00) modes of the HBAR, we investigate the temperature and power dependence of the mode linewidths which allows us to quantify and distinguish various loss mechanisms. We also compare these results to measurements in the single-excitation regime using a SC qubit and find that, in both cases, there is a significant variation of lifetimes for different modes in a single HBAR device.





[1] U. von Lüpke et al. Parity measurement in the strong dispersive regime of circuit quantum acoustodynamics. Nat. Phys. 18, 794-799



[2] V. Gokhale et al. Epitaxial bulk acoustic wave resonators as highly coherent multi-phonon sources for quantum acoustodynamics. Nat. Commun. 11, 2314 (2020).