Interference of ultrahigh frequency acoustic phonons from distant quasi-continuous sources

TL;DR

This paper demonstrates a coherent, high-frequency (20 GHz) acoustic phonon source capable of interference from distant sources, opening pathways for advanced nanoacoustic devices and applications in telecommunications and quantum technologies.

Contribution

It introduces a quasi-continuous, coherent 20 GHz phonon source using a high-Q acousto-optic resonator, enabling interference from spatially separated sources.

Findings

Acoustic phonons propagate up to 20 μm with low decay.

Coherence between distant phonon sources is demonstrated.

Potential for scalable, reconfigurable nanoacoustic devices.

Abstract

The generation of propagating acoustic waves is essential for telecommunication applications, quantum technologies, and sensing. Up to now, the electrical generation has been at the core of most implementations, but is technologically limited to a few gigahertz. Overcoming this frequency limit holds the prospect of faster modulators, quantum acoustics at higher working temperatures, nanoacoustic sensing from smaller volumes. Alternatively, the optical excitation of acoustic resonators has unlocked frequencies up to 1 THz, but in most cases, the acoustic energy cannot be efficiently extracted from the resonator into a propagating wave. Here, we demonstrate a quasi-continuous and coherent source of 20 GHz acoustic phonons, based on a ridge waveguide, structured in the vertical direction as a high-Q acousto-optic resonator. The high frequency phonons propagate up to 20 $\mu$m away from the source, with a decay rate of $\sim$1.14 dB/$\mu$m. We demonstrate the coherence between acoustic phonons generated from two distant sources through spatio-temporal interference. This concept could be scaled up to a larger number of sources, which enable a new generation of optically programmed, reconfigurable nanoacoustic devices and applications.