Visual quorum sensing in chiral suspensions: Hyperuniformity and edge currents

A well-established phenomenon in active matter is motility-induced phase separation. However, biological systems exhibit a much broader range of collective behaviors and functions due to the exchange of information among their components. In this study, we investigate a 2D active suspension where individual particles either become chiral or reverse their chirality when the density of neighboring particles within their visual cone surpasses a certain threshold-an instance of nonreciprocal interaction akin to quorum sensing in biology. By means of numerical simulations, we found that the suspension can transition between different configurations, including randomly uniform states, two-phase separation, and global strongly hyperuniform states by tuning the range and aperture of the particle visual cone. Notably, phase separation is accompanied by the emergence of stationary edge currents that circulate around the dense regions, while the particle distribution within these regions exhibits effective hyperuniformity. Large-scale particle circulation and hyperuniformity are genuine nonreciprocal effects which occur even in the absence of steric interactions. Moreover, in mixtures containing passive and quorum sensing chiral particles, $5\%$ or less of the latter suffices to generate sustained edge currents. While a full understanding of collective dynamics in biological systems proves still elusive, the findings presented here could provide inspiration for designing artificial systems, such as decentralized micro-nanorobotic systems.