  We investigate circuit complexity to characterize chaos in multiparticle
quantum systems. In the process, we take a stride to analyze open quantum
systems by using complexity. We propose a new diagnostic of quantum chaos from
complexity based on the reduced density matrix by exploring different types of
quantum circuits. Through explicit calculations on a toy model of two coupled
harmonic oscillators, where one or both of the oscillators are inverted, we
demonstrate that the evolution of complexity is a possible diagnostic of chaos.
