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Optically levitated nanoparticles in a vacuum offer a light–matter interface with broad and easy tunability of all key system parameters. However, the majority of previously reported experimental achievements in this area have only dealt with a single levitated object. Here, we demonstrate optical binding between multiple levitated objects confined in cross-polarized counter-propagating laser beams in a vacuum. We characterize the level of interparticle interaction, quantify its nonlinearity for various configurations of the system, and demonstrate its broad tunability. Our methodology for quantitative characterization of optically bound structures is supported by an extensive theoretical description and validated by numerical simulations. We believe the presented results represent a step toward the development of a framework of levitated optomechanics of complex coupled systems with a controlled level of coupling nonlinearity for experimental studies including, for example, mesoscopic entanglement.
Svak et al. (Mon,) studied this question.