Causal asymmetry of classical and quantum autonomous agents

Why is it that a ticking clock typically becomes less accurate when subject to outside noise but rarely the reverse? Here, we formalise this phenomenon by introducing process causal asymmetry—a fundamental difference in the amount of past information an autonomous agent must track to transform one stochastic process to another over an agent that transforms in the opposite direction. We then illustrate that this asymmetry can surprisingly reverse when agents possess a quantum memory. Thus, the spontaneous direction in which processes get ‘simpler’ may be different, depending on whether quantum information processing is allowed or not.