R&D: Epitaxial Bulk Acoustic Wave Resonators as Highly Coherent Multi-Phonon Sources for Quantum Acoustodynamics

Nature Communications has published an article written by Vikrant J. Gokhale, National Research Council Fellow residing at the US Naval Research Laboratory, Washington, DC, USA, Brian P. Downey, D. Scott Katzer, Neeraj Nepal, US Naval Research Laboratory, Washington, DC, USA, Andrew C. Lang, American Society for Engineering Education Postdoctoral Fellow residing at the US Naval Research Laboratory, Washington, DC, USA, Rhonda M. Stroud, and David J. Meyer, US Naval Research Laboratory, Washington, DC, USA.

Abstract: “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 × 10¹⁷ 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.“