Information about the interaction of a many-electron quantum system with its environment is encoded within the one-electron density matrix (1-RDM).
While the 1-RDM from an ensemble many-electron quantum system must obey the Pauli exclusion principle, the 1-RDM from a pure quantum system must obey additional constraints known as the generalized Pauli conditions. By examining the 1-RDM’s violation of these generalized Pauli conditions, we obtain a sufficient condition at the level of a single electron for a many-electron quantum system’s openness. As the system interacts with the environment, the more stringent generalized Pauli conditions relax to the Pauli principle, the nature and extent of this relaxation serving to quantify the degree openness of a many-electron quantum system. In an application to photosynthetic light harvesting we show that the interaction of the system with the environment (quantum noise) relaxes significant constraints imposed on the exciton dynamics by the generalized Pauli conditions. This relaxation provides a geometric (kinematic) interpretation for the role of noise in enhancing exciton transport in quantum systems.