We experimentally demonstrate critical collective behavior in a system of active colloidal particles (APs), achieved through variations of their mutual interactions using feedback control. At the transition between a swarm and a swirl we observe an explicit bifurcation dynamics of the rotational order parameter and a critical slowing down, i.e., a growth of the relaxation time by almost one order of magnitude. Additional signatures of critical dynamics, including hysteresis in presence of symmetry-breaking particle interactions, and a maximum of the susceptibility, are measured and characterized in terms of a theoretical model which is based purely on the time-reversal symmetry of the order parameter.

我们通过实验证明了活性胶体粒子 (AP) 系统中的关键集体行为，这是通过使用反馈控制改变它们的相互相互作用来实现的。在群和漩涡之间的过渡处，我们观察到旋转顺序参数的明确分岔动力学和临界减速，即弛豫时间几乎增加了一个数量级。临界动力学的其他特征，包括存在对称性破坏粒子相互作用时的滞后和最大磁化率，根据完全基于顺序参数的时间反转对称性的理论模型进行测量和表征。