The goal of this research is to develop the building blocks for scalable integrated phononic circuits, similar to those existing in the electronic and optical realms. Phononic circuits have many potential applications, including scalable computing based on mechanical vibrations, or phonons, confined at nanoscale in acoustic waveguides on a silicon chip. Nanomechanical computers of this kind promise inherent robustness to the ionising radiation that degrades semiconductor electronics in low-earth-orbit and deep space environments, as well as in close proximity to nuclear reactors and particle accelerators.

Animation of an acoustic wave launched in an acoustic waveguide formed by a high tensile stress silicon nitride membrane on a silicon chip. The acoustic wave is generated electrostatically through the force between an electrode patterned on the chip (gold) and an electrode hovering above the chip (silver sphere). Motion of the membrane can be read out interferometrically with high precision (red laser). Animation credit: N. Mauranyapin.

Recent work:

Propagation and Imaging of mechanical waves in a highly stressed single-mode acoustic waveguide

[Physical Review Applied, vol. 11, no. 6, Jun. 2019] – Phononic setup, Credit: E. Romero.

We developed a single-mode acoustic waveguide that enables robust propagation of mechanical waves. The waveguide is a highly stressed silicon-nitride membrane that supports the propagation of out of-plane modes. In direct analogy to rectangular microwave waveguides, there exists a band of frequencies over which only the fundamental mode is allowed to propagate, while multiple modes are supported at higher frequencies. We directly image the mode profiles using optical heterodyne vibration measurement, showing good agreement with theory. In the single-mode frequency band, we show low-loss propagation (approximately 1 dB/cm) for an approximately 5-MHz mechanical wave. This design is well suited for acoustic circuits interconnecting elements such as nonlinear resonators or optomechanical devices for signal processing, sensing, or quantum technologies.

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Imaging of acoustic wave tunnelling and exponential decay

Experimental imaging of acoustic wave decay through an acoustic tunnel barrier arXiv:2103.13008 (2021).

Nanomechanical circuits for transverse acoustic waves promise to enable new approaches to computing, precision biochemical sensing and many other applications. However, progress is hampered by the lack of precise control of the coupling between nanomechanical elements. Here, we demonstrate virtual-phonon coupling between transverse mechanical elements, exploiting tunnelling through a zero-mode acoustic barrier. This allows the construction of large-scale nanomechanical circuits on a silicon chip, for which we develop a new scalable fabrication technique. As example applications, we build mode-selective acoustic mirrors with controllable reflectivity and demonstrate acoustic spatial mode filtering. Our work paves the way towards applications such as fully nanomechanical computer processors and distributed nanomechanical sensors, and to explore the rich landscape of nonlinear nanomechanical dynamics.

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We gratefully acknowledge funding from:

Australian Research Council
Lockheed Martin
ARC Centre of Excellence for Engineered Quantum Systems