To generate activity

We discuss the crucial role of the frenetic fluctuation sector in the transfer of a low-entropy condition from a bath to probes. That includes the transfer of activity between bath particles and a probe (which can be spatially extended as well), but also the generation of activity in Newtonian probes coupled to driven chemical baths. The mechanism is similar: a linear instability (negative induced friction) brings the probe to an active saturation regime. We give a number of simple examples to illustrate the point, and we explain the more technical arguments of how dissipation allows the time-symmetric reactivities to steer the reduced fluctuation dynamics. If time permits, we present the structure of relaxation to nonequilibrium for macroscopic bodies, which is in fact the general background for describing response of a nonequilibrium bath to the stimuli given by probes.

References:
Ji-Hui Pei and CM, Transfer of active motion from medium to probe via the induced friction and noise. Phys. Rev. Letters136, 038301 (2026)
Aaron Beyen, CM and Jihui Pei, Coupling an elastic string to an active bath: the emergence of inverse damping. Phys. Rev. E112, L042103, 17 (2025)
CM and Karel Netočný, Relaxation to nonequilibrium. arXiv:2603.03490v2 [cond-mat.stat-mech]
Simon Krekels, CM, Ion Santra and Ruoxun Zhai, Negative Differential Heat Conductivity in a Harmonic Chain Coupled to a Particle Reservoir. arXiv:2604.00777v1 [cond-mat.stat-mech].