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

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 × 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.

Investigating Elastic Anisotropy of 4H-SiC Using Ultra-High Q Bulk Acoustic Wave Resonators

“…Beyond its exceptional material properties that confer robustness in harsh environments, monocrystalline silicon carbide resonators have recently demonstrated mechanical f • Q products beyond 1 × 10 14 in the Akhiezer regime [10] and 1 × 10 17 in the Landau-Rumer regime [11], far beyond the limit of single crystal silicon. Ultra-high mechanical Q-factors combined with a large band gap render 4H-SiC interesting in the pursuit of acoustic control of solid-state defects [12] and high-precision MEMS devices.…”

Femtometer-amplitude imaging of coherent super high frequency vibrations in micromechanical resonators

“…This device is a monolithic thickness-mode resonator with an ~2 μm thick aluminum nitride (AlN) layer sandwiched between thin molybdenum layers and capped with a layer of thin-film silicon oxide, where all layers are deposited and patterned on a 725 μm thick oxidized silicon substrate (see Methods). The BAW was designed to operate as a single-pixel within an ultrasonic fingerprint reader 30 and is similar in design to high-overtone bulk acoustic resonators (HBAR) used to generate multi-phonon Fock states 3 and to couple phonons to superconducting qubits 6 – 8 . However, the resonator presented here has high acoustic loss due to the small size of the piezoelectric component (75 µm in width), scattering caused by the large number of resonators on the top surface (i.e., resonator array), and the layered SiO2/Mo/AlN structure, resulting in behavior more like a low- Q , solidly-mounted BAW.…”

“…The presented measurement and analysis methods will benefit the design and optimization of surface acoustic wave 4 , 5 , 9 and bulk acoustic wave 1 – 3 , 6 – 8 resonators that are now critical for 5G wireless communications 1 , 2 and acoustic quantum operations 3 – 9 . In particular, the large improvement in the noise floor will allow these devices to be characterized at the typical power levels used during operation, rather than having to overdrive them to be able to get a measurable signal, mitigating the effects of geometric and material nonlinearities during characterization.…”

“…Acoustic resonators operating in the super high frequency range are also being aggressively pursued for quantum information, where they are used for quantum state generation 3 , 4 , as well as state transfer and entanglement between qubits 5 . Operation in the range of 4 to 10 GHz and with high Q is necessary so that they can strongly couple to microwave superconducting qubits 3 – 8 and electron spin qubits 9 . Furthermore, resonators with a high frequency – quality factor product, , will allow near-quantum-limited behavior through ground-state cooling while operating at temperatures that can be achieved without a cryostat ( ) 10 , 11 .…”

Sideband Control of a Multimode Quantum Bulk Acoustic System

“…Another contributing loss factor is the polycrystalline form of the AlN, which may degrade the otherwise excellent lifetimes in the bulk acoustic resonator. Promisingly, recent experimental advances allow for building completely epitaxial bulk acoustic wave resonators with a metallic bottom electrode, creating highly coherent phonon modes [31]. The Xmon qubit has symmetric junctions and a maximum frequency of 5.97 GHz.…”