Inducing a bound state between active particles

TL;DR

This paper demonstrates that two active particles can form a bound state through coupling with a driven nonequilibrium environment, revealing novel trapping phenomena and analogies with Cooper pairing.

Contribution

It introduces a mechanism for bound state formation between active particles mediated by a driven environment, a novel concept in active matter physics.

Findings

Bound states form at high persistence (low effective temperature).

Active probes become trapped in bound states under time-scale separation.

Analogy with Cooper pairing in a pilot-wave framework.

Abstract

We show that two active particles can form a bound state by coupling to a driven nonequilibrium environment. We specifically investigate the case of two mutually noninteracting run-and-tumble probes moving on a ring, each in short-range interaction with driven colloids. Under conditions of time-scale separation, these active probes become trapped in bound states. In fact, the bound state appears at high enough persistence (low effective temperature). From the perspective of a co-moving frame, where colloids are in thermal equilibrium and the probes are active and driven, an appealing analogy appears with Cooper pairing, as electrons can be viewed as run-and-tumble particles in a pilot-wave picture.