Observing the dynamics of octupolar structural transitions in trapped-ion clusters

TL;DR

This study observes and analyzes structural transitions in 3D trapped-ion clusters, revealing symmetry-breaking, hysteresis, and stochastic switching, thus providing insights into collective dynamics and phase transitions in controllable mesoscopic systems.

Contribution

It demonstrates real-time imaging of structural transitions in 3D ion clusters, identifying octupole order parameters and dynamical signatures, advancing understanding of symmetry and collective modes.

Findings

Observation of parity-odd octupole order parameters

Detection of a Higgs-like mode indicating symmetry-breaking

Identification of hysteresis and stochastic switching phenomena

Abstract

Interacting many-particle systems can self-organize into a rich variety of crystalline structures. While symmetry provides a powerful framework for predicting whether transitions between crystal states are continuous or discontinuous, collective lattice dynamics offer complementary insights into the microscopic mechanisms that drive these transitions. Trapped laser-cooled ions present a pristine and highly controllable few-body system for studying this interplay of symmetry and dynamics. Here, we use real-time fluorescence imaging while deforming the trap potential to observe a variety of structural transitions in three-dimensional (3D), unit-cell-like ion clusters. We identify a set of transitions signaled by parity-odd octupole order parameters, and probe their distinct dynamical signatures. Our observations reveal the softening of a collective Higgs-like mode indicating spontaneous symmetry-breaking, hysteresis resulting from a catastrophe where a metastable state vanishes abruptly, and stochastic switching between metastable states of differing symmetries. We also uncover a remarkable coincidence of symmetry-breaking and discontinuous transitions, analogous to a thermodynamic triple point. Our results establish 3D trapped-ion clusters as a versatile platform to engineer complex potential energy landscapes, opening new avenues for studies of reaction kinetics, geometric frustration, and related phenomena in mesoscopic platforms.