Understanding the coherence properties of HBARs in the classical and quantum regimes

Raquel García Bellés

PhD student at HyQu

Abstract

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High overtone bulk acoustic wave resonators (HBARs) have been successfully integrated with superconducting qubits into hybrid quantum systems with many applications in quantum information technologies. Their success strongly relies on the excellent coherence properties of the mechanical modes. Nevertheless, a full understanding of the limiting loss mechanisms affecting multimode HBAR devices is still missing.
In this talk, I discuss the influence of different loss mechanisms in our HBAR devices, with a particular focus on two-level-system (TLS) loss. I present our characterization of the quality factors of hundreds of mechanical modes in a several-GHz frequency span, and show evidence that TLS loss is present but only has a minimal contribution at low temperatures and powers. This is consistent with the lifetimes measured for the HBAR modes in the quantum regime through a flux tunable superconducting qubit. In addition, the absence of frequency noise caused by TLS enables the coherence times (T2*) to be lifetime (T1) limited, reaching ~1ms without dynamical decoupling. These results highlight the relevance of HBARs as a quantum information processing platform.