Nonequilibrium phases in mixtures of active and passive particles

Active systems composed of self-propelled particles are intrinsically out of equilibrium. Due to the breaking of detailed balance at the individual particle level, they exhibit complex dynamic phenomena not observed in their equilibrium counterparts. For instance, distinct nonequilibrium phases such as a demixed state and motility induced phase separated state (MIPS) can arise in a binary mixture of passive and active particles. Here, we map the computational phase diagram of a binary mixture of active and passive particles as a function of orientational interactions and Peclet number and observe new emergent behavior of dynamical clustering and a polar band of active particles. This computational study helps us to illuminate observations of experiments we developed consisting of passive colloid particles immersed in a bath of bacteria. By quantifying fluctuations and correlations between passive particles in both simulations and experiments, we quantify how far the system is from equilibrium.