Contractivity of the Hilbert--Schmidt Speed in Unital Quantum Channels: Foundation for Witnessing Non-Markovianity and Discriminating Unital from Non-Unital Markovian Dynamics

arXiv:2607.05619v1 Announce Type: new Abstract: We investigate the Hilbert--Schmidt speed (HSS), a geometric indicator defined through the Hilbert--Schmidt norm of the tangent vector to a parametrized family of quantum states, under general open-system dynamics. Working in the framework of finite-d