# Long-range Velocity Correlations from Active Dopants

## TL;DR

This paper demonstrates that a small fraction of active particles can induce long-range velocity correlations in dense passive systems, explained through a continuum theory and validated by simulations.

## Contribution

It introduces a continuum model explaining how active dopants generate long-range velocity correlations in passive matter, supported by extensive simulations.

## Key findings

- Active dopants induce long-range velocity correlations.
- The continuum theory accurately predicts the effects of activity parameters.
- Simulations confirm the decoupling of density and activity roles.

## Abstract

One of the most remarkable observations in dense active matter systems is the appearance of long-range velocity correlations without any explicit aligning interaction (of e.g.\ Vicsek type). Here we show that this kind of long range velocity correlation can also be generated in a dense athermal passive system by the inclusion of a very small fraction of active Brownian particles. We develop a continuum theory to explain the emergence of velocity correlations generated via such active dopants. We validate the predictions for the effects of magnitude and persistence time of the active force and the area fractions of active or passive particles using extensive Brownian dynamics simulation of a canonical active-passive mixture. Our work decouples the roles that density and activity play in generating long range velocity correlations in such exotic non-equilibrium steady states.