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arXiv:2602.08772

Heterogeneous Optically-Detected Spin-Acoustic Resonance in Solid-State Molecular Thin-film

Kuan-Cheng Chen, Yongqiang Wen, Xiaotian Xu, Max Attwood, Jingdong Xu, Chen Fu, Sami Ramadan, Shang Yu, Sandrine Heutz, Mark Oxborrow

quant-phcond-mat.mtrl-sciphysics.app-phSubmitted Feb 9, 2026• Announced Feb 10, 2026

Abstract

We report an implementation of spin-acoustic resonance in pentacene thin films integrated on a high-quality-factor (high-Q) surface acoustic wave (SAW) resonator on a lithium niobate substrate. Heterogeneous optically detected spin-acoustic resonance (HODSAR) is an optically detected spin-resonance measurement in which the resonant drive is delivered mechanically by a surface acoustic wave (SAW). By leveraging the photo-excited triplet state of pentacene at room temperature, we demonstrate coherent spin manipulation via acoustic driving under zero externally applied magnetic field. The heterogeneously integrated device, referred to as HODSAR, utilizes spin-phonon coupling to achieve mechanically driven, zero-field spin resonance, opening avenues for room-temperature mechanically addressable spin control and device integration. We show that the high-Q multimode response of the SAW resonator enables spectrally selective acoustic addressing of triplet transitions near 105 MHz. Coherent control is evidenced by Rabi oscillations, with a Rabi frequency that increases linearly with the square root of the applied RF input power over the measured drive range, consistent with driven two-level dynamics under acoustic excitation. These results establish spin-acoustic resonance in a heterogeneously integrated molecular thin-film platform and provide a quantitative basis for benchmarking mechanically mediated spin control.

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We report an implementation of spin-acoustic resonance in pentacene thin films integrated on a high-quality-factor (high-Q) surface acoustic wave (SAW) resonator on a lithium niobate substrate. Heterogeneous optically detected spin-acoustic resonance (HODSAR) is an optically detected spin-resonance measurement in which the resonant drive is delivered mechanically by a surface acoustic wave (SAW). By leveraging the photo-excited triplet state of pentacene at room temperature, we demonstrate coherent spin manipulation via acoustic driving under zero externally applied magnetic field. The heterogeneously integrated device, referred to as HODSAR, utilizes spin-phonon coupling to achieve mechanically driven, zero-field spin resonance, opening avenues for room-temperature mechanically addressable spin control and device integration. We show that the high-Q multimode response of the SAW resonator enables spectrally selective acoustic addressing of triplet transitions near 105 MHz. Coherent control is evidenced by Rabi oscillations, with a Rabi frequency that increases linearly with the square root of the applied RF input power over the measured drive range, consistent with driven two-level dynamics under acoustic excitation. These results establish spin-acoustic resonance in a heterogeneously integrated molecular thin-film platform and provide a quantitative basis for benchmarking mechanically mediated spin control.

The feasibility of active pre-cooling (APC) by temporarily over-coupling microwave cavity modes to a low-noise amplifier acting as an active cold load was demonstrated, offering an effective method to reduce thermal photon occupancy without cryogenic cooling. The potential of the organic radical BDPA as a tunable qubit medium with remarkably long spin-lattice and spin coherence relaxation times was assessed, comparing favorably with state-of-the-art molecular qubit media. A high-quality surface acoustic wave device integrated with pentacene-deposited molecular thin films was developed to achieve heterogeneous optically-detected spin acoustic resonance (HODSAR), enabling efficient zero-field spin control at room temperature via spin-phonon coupling. Through the construction of specialized experimental setups, the effectiveness of these techniques was demonstrated, facilitating pre-cooling of cavity modes, enhancing coherence times in qubit media, and achieving precise spin manipulation. While APC offers advantages over methods like masers and anti-masers, challenges such as the need for fast, low-loss microwave switches remain. The BDPA radicals showed significant promise for spin ensemble, and the SAW-based HODSAR device provides a scalable platform for spin manipulation in quantum technologies.

Surface-acoustic-wave (SAW) resonators are a promising platform for constructing hybrid quantum systems, where confined acoustic waves enable strong interaction with various physical systems. Focusing SAW resonators, reducing mode volume while suppressing diffraction losses, have recently been investigated for application in such hybrid systems. However, the resonator leads to additional transverse-mode resonances, which cause undesired responses. In this work, we develop focusing SAW resonators on a thin-film lithium niobate on sapphire. A film thinner than the SAW wavelength allows a highly confined acoustic-wave mode to be localized on the substrate surface. By using contoured electrodes following a two-dimensional Gaussian beam shape, we make the SAW mode focused to nearly a diffraction-limited and confirm it via optical imaging. Furthermore, by engineering the spatial mode overlap of the interdigital transducer electrodes, we suppress the excitation of higher-order transverse modes.

Surface acoustic wave (SAW) phonon coupling with nitrogen-vacancy (NV) center spins in diamond offers a promising platform for on-chip quantum phononic manipulations. Although an ensemble of NV centers coupled to a common SAW phonon mode enables superradiance and collective quantum control, achieving a tunable superradiant phase transition remains challenging. Here, we show that optically driving NV centers level transitions enhances the effective spin-phonon coupling, triggering a SAW phonon superradiant phase transition in the weak-coupling regime. We also demonstrate that above a critical threshold, the driving light rapidly switches on the phonon superradiance--a dynamic effect that persists in finite-number NV ensembles. Our results provide a controllable route to coherent phonon-NV spin manipulation in solid state quantum devices.

Quantum excitations of macroscopic surface acoustic waves (SAWs) have been tailored to control, communicate, and transduce stationary and flying quantum states. However, the limited lifetime of these hybrid quantum systems remains critical obstacles to extend their applications in quantum information processing. Here, we present potentials of thin film aluminum nitride to on-chip integrated phonons with superconducting qubits over previous bulk piezoelectric substrates. We have reported high-quality thin film GHz-SAW resonators with the highest internal quality factor Qi of 4.92×104 in the quantum regime. The internal losses of SAW resonators are systematically investigated by tuning the parameters of sample layout, power, and temperature. Our results manifest that SAWs on piezoelectric films are readily integrated with standard fabrication of Josephson junction quantum circuits and offer excellent acoustic platforms for high-coherence quantum acoustodynamics architectures.

Thin-film surface acoustic wave (SAW) devices exhibit high quality factors and are promising candidates for quantum transducers, with significant potential for on-chip integration with high-coherence superconducting quantum circuits and optical resonators. However, the experimental demonstration of strong coupling between thin-film SAWs and superconducting qubits in the quantum regime remains a considerable challenge. In this study, we demonstrate strong coupling between a ScAlN thin-film SAW resonator and a high-coherence qubit on the same substrate, where the enhanced qubit coherence was achieved through selective ScAlN etching. Distinct multimode anticrossings are observed in both the qubit and SAW resonator frequency spectra, with extracted coupling strengths closely matching theoretical predictions. Additionally, we investigate qubit decay and the dissipation properties of the SAW resonator in the SAW-qubit hybrid system. Our results confirm the feasibility of integrating thin-film SAW devices with high-coherence superconducting circuits and offer valuable insights for optimizing the performance of such hybrid systems.