Acoustic Pancharatnam-Berry Geometric Phase

TL;DR

This paper demonstrates, both theoretically and experimentally, that the Pancharatnam-Berry geometric phase can be observed in inhomogeneous sound waves, enabling advanced wavefront manipulation and potential applications in acoustic technologies.

Contribution

It introduces the first observation of the PB phase in sound waves, extending geometric phase concepts from optics to acoustics with practical metasurface implementations.

Findings

Demonstrated acoustic PB phase in surface sound waves

Realized acoustic PB metasurfaces for wavefront control

Generated acoustic vortices using spin-orbit interaction

Abstract

Geometric phases provide a unified framework for understanding diverse phenomena in quantum and classical physics. The Pancharatnam-Berry (PB) geometric phase, arising from variation of optical transverse polarization, has transformed light manipulation. However, this phase has never been observed in sound waves due to their curl-free longitudinal nature. Here, we theoretically and experimentally demonstrate that the PB phase can emerge in general inhomogeneous sound waves with polarization evolution of velocity field. Using surface sound waves as an example, we uncover the intriguing Janus property of the PB phase arising from spin-momentum locking, and realize acoustic PB metasurfaces for versatile wavefront manipulation. We further extend the mechanism to free-space structured sound and realize acoustic $q$-plate for generating acoustic vortices through spin-orbit interaction. Our work provides new insights into sound wave properties and enables the manipulation of inhomogeneous acoustic fields via the PB phase, with potential applications in acoustic communications and imaging.