Irreversibility, heat and information flows induced by non-reciprocal interactions*

In recent years, much progress was made in understanding the fundamental principles governing living and artificial complex systems that naturally operate far from thermal equilibrium. However, so far, little attention has been paid to the implications of nonreciprocal interactions, which cannot be represented by interaction Hamiltonians, contrasting all interactions traditionally considered in statistical mechanics and thermodynamics. Such interactions emerge commonly in biological, chemical and feedback systems, and are widespread in active matter. They further have applications in (quantum) engineering, and are experimentally realised in colloidal systems. In this talk, I will use simple time- and space-continuous Langevin models to discuss the fundamental thermodynamic implications of nonreciprocity [1], employing concepts from stochastic thermodynamics and information theory. In particular, under fairly general conditions, nonreciprocal coupling implies a steady energy flow through the system, which is necessarily accompanied by an information flow. The entropy balance of an individual nonreciprocally coupled subsystem contains an information-theoretical contribution, giving rise to a generalised second law like the ones known for systems under the influence of external feedback control. Remarkably, nonreciprocal coupling can induce an anomalous heat flow from cold to hot, somewhat resembling the effect of an 'Maxwell demon'. Nonreciprocal interactions can further be used to engineer nontrivial memory [2]. Lastly, we also consider the impact of nonreciprocal coupling on collective behaviour and show that it can induce long-range order.