Epitaxial bulk acoustic wave resonators as highly coherent multi-phonon sources for quantum acoustodynamics

• Published in: Nature communications Vol. 11; no. 1; pp. 2314 - 9
• Main Authors: Gokhale, Vikrant J., Downey, Brian P., Katzer, D. Scott, Nepal, Neeraj, Lang, Andrew C., Stroud, Rhonda M., Meyer, David J.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 08.05.2020; Nature Publishing Group; Nature Portfolio
• Subjects: 142/126; 147/143; 147/3; 639/166/987; 639/301/119/544; 639/925/357/995; 639/925/927/481; Acoustic coupling; Acoustic impedance; Acoustic waves; Acoustics; Bulk acoustic wave devices; Coupling; Crystal defects; Epitaxial growth; Gallium nitrides; Grain boundaries; Humanities and Social Sciences; Impedance matching; Information processing; Information storage; Interfaces; multidisciplinary; Niobium nitride; Phonons; Piezoelectricity; Q factors; Quantum phenomena; Qubits (quantum computing); Relaxation time; Resonators; Science; Science (multidisciplinary); Silicon carbide; Silicon substrates; Superconductivity; Surface roughness
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-020-15472-w

Solid-state quantum acoustodynamic (QAD) systems provide a compact platform for quantum information storage and processing by coupling acoustic phonon sources with superconducting or spin qubits. The multi-mode composite high-overtone bulk acoustic wave resonator (HBAR) is a popular phonon source well suited for QAD. However, scattering from defects, grain boundaries, and interfacial/surface roughness in the composite transducer severely limits the phonon relaxation time in sputter-deposited devices. Here, we grow an epitaxial-HBAR, consisting of a metallic NbN bottom electrode and a piezoelectric GaN film on a SiC substrate. The acoustic impedance-matched epi-HBAR has a power injection efficiency >99% from transducer to phonon cavity. The smooth interfaces and low defect density reduce phonon losses, yielding ( f × Q ) and phonon lifetimes up to 1.36 × 10 17  Hz and 500 µs respectively. The GaN/NbN/SiC epi-HBAR is an electrically actuated, multi-mode phonon source that can be directly interfaced with NbN-based superconducting qubits or SiC-based spin qubits. Acoustic resonators may find application for qubit coupling in compact quantum information and processing systems. Here the authors show a multi-phonon source with high quality factors and long phonon lifetimes via epitaxial high-overtone bulk acoustic resonators.