Using quantum theory to simplify input–output processes

Abstract

Responding to the environment is easier with quantum mechanics Can a quantum goldfish exhibit more complex behaviour than a classical dolphin? In complexity science, the complexity of an input-output process – a system that reacts differently when supplied with different environmental stimuli – can be quantified by the minimal memory needed to reproduce the process’s observed behaviour. This reflects the intuition that a goldfish – that remembers very little – can only exhibit fairly simple input-output behaviour. Here we show how these ideas can radically change when generalized to the quantum domain. A quantum system may exhibit behaviour that appears considerably more complex than a classical system that has significantly more memory.