The Makri group has developed an approach to describe the time evolving of the “purity” (idempotency) for an initially localized state of a symmetric two-level system coupled to a dissipative bath based on numerically exact real-time path integral methods. These findings caution against using purity as a measure of decoherence in the dynamics of quantum dissipative systems.
S Chatterjee and N Makri, “Recovery of Purity in Dissipative Tunneling Dynamics”, J. Phys. Chem. Lett. 11, 8592–8596 (2020) https://dx.doi.org/10.1021/acs.jpclett.0c02513