Engineering Electron–Phonon Coupling of Quantum Defects to a Semiconfocal Acoustic Resonator

• Published in: Nano letters Vol. 19; no. 10; pp. 7021 - 7027
• Main Authors: Chen, Huiyao, Opondo, Noah F, Jiang, Boyang, MacQuarrie, Evan R, Daveau, Raphaël S, Bhave, Sunil A, Fuchs, Gregory D
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 09.10.2019
• Subjects: Nitrogen-vacancy center; diamond; MEMS; silicon carbide; bulk acoustic resonator
• ISSN: 1530-6984; 1530-6992; 1530-6992
• DOI: 10.1021/acs.nanolett.9b02430

Diamond-based microelectromechanical systems (MEMS) enable direct coupling between the quantum states of nitrogen-vacancy (NV) centers and the phonon modes of a mechanical resonator. One example, a diamond high-overtone bulk acoustic resonator (HBAR), features an integrated piezoelectric transducer and supports high-quality factor resonance modes into the gigahertz frequency range. The acoustic modes allow mechanical manipulation of deeply embedded NV centers with long spin and orbital coherence times. Unfortunately, the spin-phonon coupling rate is limited by the large resonator size, >100 μm, and thus strongly coupled NV electron–phonon interactions remain out of reach in current diamond BAR devices. Here, we report the design and fabrication of a semiconfocal HBAR (SCHBAR) device on diamond (silicon carbide) with f × Q > 1012 (>1013). The semiconfocal geometry confines the phonon mode laterally below 10 μm. This drastic reduction in modal volume enhances defect center coupling to a mechanical mode by 1000 times compared to prior HBAR devices. For the native NV centers inside the diamond device, we demonstrate mechanically driven spin transitions and show a high strain-driving efficiency with a Rabi frequency of (2π)­2.19(14) MHz/V p, which is comparable to a typical microwave antenna at the same microwave power, making SCHBAR a power-efficient device useful for fast spin control, dressed state coherence protection, and quantum circuit integration.