In living materials, collective motion often manifests as flow vortices and jets, forming what is known as active turbulence. Using a continuum theory of active nematics and employing an information-theoretic divergence measure, we report on the existence of an activity threshold, beyond which the behavior of the active nematic system substantially changes. Specifically, we show that at this activity threshold the defect pathlength reaches its maximum, velocity correlation length peaks, and nonlinear dependence of flow mixing rate on activity vanishes. We further show that this activity threshold is well separated from the threshold for topological defects nucleation and is a robust feature of the system across different parameter values, and independent of system size. The results offer new insights into characterizing nonequilibrium evolution of active materials with varying activity levels.

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• Biological fluid dynamics
• Active defects
• Active gels
• Biological liquid crystals
• Complex fluids