Uhlmann and scalar Wilczek-Zee phases of degenerate quantum systems

Abstract: The Wilczek-Zee (WZ) holonomy arises in degenerate states while the Uhlmann holonomy characterizes finite-temperature topology. We investigate possible relationships between the Uhlmann phase and the scalar WZ phase, which reflects the Uhlmann and WZ holonomy respectively, in an exemplary four-level model with two doubly degenerate subspaces. Through exactly solutions, we contrast the behavior of the Uhlmann and WZ connections and their associated phases. In the zero-temperature limit, the Uhlmann phase may or may not agree with the scalar WZ phase of the degenerate ground states due to the underlying topology. Some conditions are derived in an analytic analysis, under which the Uhlmann phase in the zero-temperature limit converges to the scalar WZ phase. We also briefly discuss possible realizations or simulations of the phenomena as well as their implications.