Compact phononic circuits guide sound at gigahertz frequencies for chip-scale devices

Phononic circuits are emerging devices that can manipulate sound waves (i.e., phonons) in ways that resemble how electronic circuits control the flow of electrons. Instead of relying on wires, transistors and other common electronic components, these circuits are based on waveguides, topological edge structures and other components that can guide phonons.

Phononic circuits are opening new possibilities for the development of high-speed communication systems, quantum information systems and various other technologies.

To be compatible with existing infrastructure, including current microwave communication systems, and to be used to develop highly performing quantum technologies, these circuits should ideally operate at gigahertz (GHz) frequencies. This essentially means that the sound waves they generate and manipulate oscillate billions of times per second.

Researchers at University of Science and Technology of China, Penn State University and other institutes recently developed new compact phononic circuits that can reliably guide sound waves at 1.5 GHz.

These new circuits, introduced in a paper published in Nature Electronics, could be used to create both quantum and classical devices that could advance communications, sensing and information processing.

“We were inspired by the success of integrated photonics and wanted to show that similar concepts could be applied to sound waves,” Mourad Oudich, co-first author of the paper, told Tech Xplore.

“Our goal was to build tiny, chip-scale phononic circuits operating at GHz frequencies that are compact, reconfigurable, and robust enough for real-world applications.”

The circuits introduced by these researchers are designed to confine acoustic waves at GHz frequencies, guiding them through tiny waveguides on a chip. Notably, these wavelengths sit directly on a substrate, which could facilitate the circuits’ large-scale fabrication.

“Our phononic circuits are made of microscopic ‘highways’ that guide sound instead of light,” explained Oudich.

“By arranging these waveguides in special patterns, we create topological pathways where sound travels smoothly even around corners or defects. This makes the circuits more reliable and much smaller than traditional acoustic devices.”

To evaluate their phononic circuits, the researchers monitored the propagation of phonons inside them using a high-resolution scanning optical vibrometer. This is a device that can measure subtle vibrations on a surface, such as those produced by the movement of phonons through the waveguides.

Oudich and his colleagues injected phonons into their circuits’ edge channels and showed that they successfully traveled through the system without scattering. They also performed a so-called Mach-Zehnder Interferometer test, which confirmed the reconfigurability of their phononic devices (i.e., their ability to rapidly alter the paths of phonons).

“We demonstrated, for the first time, topological sound transport and a phononic Mach–Zehnder interferometer directly on a chip at gigahertz frequencies,” said Oudich.

“These advances could lead to new acoustic filters for communications and even help in developing phonon-based components for future quantum technologies.”

The reconfigurable devices developed by this team of researchers could soon be used to fabricate a wide range of technologies, including quantum processors, high-precision sensors and new hybrid communication systems. Oudich and his colleagues are currently planning further research aimed at combining their circuits with existing electronics and components.

“We now aim to integrate the phononic circuits with electronic and photonic systems, making them useful for hybrid technologies,” added Oudich.

“In the long run, we want to build a full ‘phononic toolbox’ for advanced information processing and sensing.”

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