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arXiv:2509.14728 · Journal of Applied Physics

Proposal of cavity quantum acoustodynamics platform based on lithium niobate-on-sapphire chip

Xin‐Biao Xu, Lintao Xiao, Bo Zhang, Weiting Wang, Jia-Qi Wang, Yu Zeng, Yuan-Hao Yang, Baozhen Wang, Xiaoxuan Pan, Guang‐Can Guo, Luyan Sun, Chang‐Ling Zou

Published Mar 16, 2026• 1 citation
arXivHTMLPDF

Abstract

A scalable hybrid cavity quantum acoustodynamics (QAD) platform is proposed. The architecture integrates superconducting transmon qubits with phononic integrated circuits on a single chip made by a lithium niobate-on-sapphire substrate. The platform supports tightly confined and guided phononic modes in unsuspended waveguides and microring structures, while the superconducting qubits reside on the sapphire substrate. Efficient piezoelectric coupling between the phononic modes and transmon qubits can be achieved using interdigital transducers as part of the qubit’s shunt capacitance. Numerical calculations demonstrate the feasibility of achieving strong coupling between the phononic microring resonator and the transmon qubit. Remarkably, we show that a single pair of interdigital transducer fingers is sufficient to yield a coupling strength of g/2π≈1.3 MHz for the quasi-Love mode. This hybrid cavity QAD platform opens up new opportunities for quantum information processing and the study of novel quantum acoustic phenomena.

DOI
10.1063/5.0307570

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A scalable hybrid cavity quantum acoustodynamics (QAD) platform is proposed. The architecture integrates superconducting transmon qubits with phononic integrated circuits on a single chip made by a lithium niobate-on-sapphire substrate. The platform supports tightly confined and guided phononic modes in unsuspended waveguides and microring structures, while the superconducting qubits reside on the sapphire substrate. Efficient piezoelectric coupling between the phononic modes and transmon qubits can be achieved using interdigital transducers as part of the qubit’s shunt capacitance. Numerical calculations demonstrate the feasibility of achieving strong coupling between the phononic microring resonator and the transmon qubit. Remarkably, we show that a single pair of interdigital transducer fingers is sufficient to yield a coupling strength of g/2π≈1.3 MHz for the quasi-Love mode. This hybrid cavity QAD platform opens up new opportunities for quantum information processing and the study of novel quantum acoustic phenomena.
Previous demonstrations of quantum acoustic systems have been limited to isolated devices, with limited capability to route phonons and interconnect multi-port acoustic elements for further extension. Here, we demonstrate a scalable architecture for circuit quantum acoustodynamics (cQAD) by integrating superconducting qubits with suspension-free phononic integrated circuits (PnICs). Coherent coupling between tunable transmon qubits and waveguide-integrated phononic cavities, including Fabry-Perot cavities via monolithic integration and microring cavities via flip-chip assembly, has been achieved, producing a pronounced enhancement of phonon emission with a Purcell factor of ~19. These devices represent elementary building blocks for scalable phononic circuits, establishing the foundation for phonon-based quantum information processors and the testbed for novel quantum acoustic phenomena.
We propose a novel scheme for efficient and low-noise microwave-to-optical quantum transduction based on cavity-enhanced Brillouin interaction between telecom photons and 10 gigahertz phonons on a lithium niobate-on-Sapphire chip. By employing a dual-microring cavity design and tailoring the geometry dispersion, triply-resonant and phase-matching conditions can be achieved for the backward Brillouin process, resulting in strong vacuum coupling strengths between the confined phononic and photonic modes. Our numerical analysis, taking into account the material anisotropy of lithium niobate and sapphire, predicts near-unity internal conversion efficiency with only sub-milliwatt pump power. The unsuspended all-solid-state architecture offers superior mechanical stability and robustness, overcoming a major challenge in piezo-optomechanical systems. Furthermore, the broadband nature of the Brillouin process enables multi-channel conversion, a key advantage over existing approaches. This versatile platform opens up exciting opportunities for scalable quantum processors with hybrid photonic-phononic-superconducting integrated circuits.
We demonstrate a giant atom by coupling a superconducting transmon qubit to a lithium niobate phononic waveguide at two points separated by about 600 acoustic wavelengths, with a propagation delay of 125 ns. The giant atom yields non-Markovian relaxation dynamics characterized by phonon backflow and a frequency-dependent effective decay rate varying four-fold over merely 4 MHz, corresponding to a Purcell factor exceeding 40. Exploiting this frequency-dependent dissipation, we prepare quantum superposition states with high purity. Our results establish phononic integrated circuits as a versatile platform for giant-atom physics, providing highly tunable quantum devices for advanced quantum information processing.
Coherent transduction of quantum states from the microwave to the optical domain can play a key role in quantum networking and distributed quantum computing. We present the design of a piezo-optomechanical device formed in a hybrid lithium niobate on silicon platform, that is suitable for microwave-to-optical quantum transduction. Our design is based on acoustic hybridization of an ultra-low mode volume piezoacoustic cavity with an optomechanical crystal cavity. The strong piezoelectric nature of lithium niobate allows us to mediate transduction via an acoustic mode which only minimally interacts with the lithium niobate, and is predominantly silicon-like, with very low electrical and acoustic loss. We estimate that this transducer can realize an intrinsic conversion efficiency of up to 35% with <0.5 added noise quanta when resonantly coupled to a superconducting transmon qubit and operated in pulsed mode at 10 kHz repetition rate. The performance improvement gained in such hybrid lithium niobate-silicon transducers make them suitable for heralded entanglement of qubits between superconducting quantum processors connected by optical fiber links.
Mechanical resonators are emerging as a powerful platform for quantum information science, offering compactness, long coherence times, and scalability. In this thesis, we explore a circuit quantum acoustodynamics (cQAD) device based on integrating high-overtone bulk acoustic resonators (HBARs) with superconducting transmon qubits. This architecture harnesses the dense mode structure and high quality factors of HBARs alongside the fast control and high-fidelity readout of superconducting qubits. We demonstrate essential building blocks for phonon-based quantum operations, including direct measurements of phonon number and parity, as well as Wigner tomography of nonclassical states. We also realize Schrödinger cat states in a mechanical resonator with an effective mass of 16.2 micrograms and investigate their decoherence dynamics. Additionally, we demonstrate the creation and coherent control of a mechanical qubit enabled by strong single-phonon anharmonicity. Building on these capabilities, we introduce the concept of Acoustic Resonator-Based Quantum Circuits (ARQCs), where multiple phonon modes act as encoded qubits and a single transmon mediates interactions between them. This architecture supports compact, reconfigurable, and highly scalable quantum circuits capable of controlling hundreds of modes within a single device. Our experimental and simulation results position the cQAD platform as a compelling and versatile candidate for future quantum information processing technologies.
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.