Abstract
Crowd synchrony, which corresponds to the synchronization of different and independent oscillators that interact with each other via a common intermediate, is ubiquitous in many fields. Here, we experimentally demonstrate the effect of crowd synchrony, analogous to that of the Millennium Bridge, by resorting to coupled lasers. When the number of lasers is below a critical number, there is no synchronization, but after reaching the critical number, the lasers instantaneously synchronize. We show that the synchronization of the lasers as a function of their number follows a first-order-like transition, and that our experimental results are in good agreement with those predicted by theoretical models.
Highlights
Synchronization of independent dynamical elements via an intermediate medium plays an important role in biology, chemistry, engineering, and physics
The pedestrians, each walking at different pace and speed, caused small lateral oscillations to the bridge, which in turn caused the pedestrians to sway in step in order to retain balance, dramatically amplifying the oscillations of the bridge and synchronizing the pedestrians [9,11,14,15]
The effect was modeled as crowd synchronization [Fig. 1(a)], where the lateral oscillations of the bridge were attributed to a combination of oscillations and synchronization that critically depends on the number of pedestrians [10,11]
Summary
Synchronization of independent dynamical elements via an intermediate medium plays an important role in biology, chemistry, engineering, and physics. Crowd synchrony was theoretically predicted with coupled lasers, where coupling between M independent (star) lasers (analogous to pedestrians) is mediated by a central (hub) laser (analogous to the bridge) operating below lasing threshold [Fig. 1(b)] [16]. Phase synchronization of laser arrays was achieved with nonlinear (spatiotemporal) coupling by means of a saturable absorber, demonstrating improvement in finding a ground-state solution in comparison with linear coupling [30] While these experimental investigations yielded many exciting results on synchronization, they did not provide information on the nature of the transition to synchronization. We observed a first-order transition to synchronization as the number of star lasers crosses a critical number Mc that depends on the coupling strength K between the two DCLs and follows a power law with.
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