Emergent activity powers a path to chaos for pairs of acoustically trapped spheres
Abstract
Pairs of spheres sharing an acoustic trap sometimes spin intermittently despite having no self-propulsion, no obvious power source, and no symmetry-breaking mechanism, switching between rocking and spinning within a single trajectory. Nonreciprocal wave scattering powers this emergent activity, and drag shapes their dynamics by coupling rotations to translations. Mismatched pairs can pass through a supercritical Hopf bifurcation into a quasiperiodic torus on which the pair's orbit reverses regularly and, farther from equilibrium, into deterministic chaos. Experiments motivate this mechanism and share its qualitative signatures; simulations reveal a full noise-free route from passivity to chaos, and suggest how analogous dynamics can emerge in other active-matter systems.
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BibTeX
@misc{gronert2026emergent,
title = {{Emergent activity powers a path to chaos for pairs of acoustically trapped spheres}},
author = {Matthew K. Gronert and Ben Cao and Ella M. King and David G. Grier},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.37946},
eprint = {2609.37946},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.37946},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Emergent activity powers a path to chaos for pairs of acoustically trapped spheres
AU - Matthew K. Gronert
AU - Ben Cao
AU - Ella M. King
AU - David G. Grier
PY - 2026
DA - 2026/09/29
PB - arXiv
DO - 10.48550/arxiv.2609.37946
UR - https://arxiv.org/abs/2609.37946
AB - Pairs of spheres sharing an acoustic trap sometimes spin intermittently despite having no self-propulsion, no obvious power source, and no symmetry-breaking mechanism, switching between rocking and spinning within a single trajectory. Nonreciprocal wave scattering powers this emergent activity, and drag shapes their dynamics by coupling rotations to translations. Mismatched pairs can pass through a supercritical Hopf bifurcation into a quasiperiodic torus on which the pair's orbit reverses regularly and, farther from equilibrium, into deterministic chaos. Experiments motivate this mechanism and share its qualitative signatures; simulations reveal a full noise-free route from passivity to chaos, and suggest how analogous dynamics can emerge in other active-matter systems.
ER -