A simple analytical expression of quantum Fisher and Skew information and their dynamics under decoherence channels

Abstract

In statistical estimation theory, it has been shown previously that the Wigner–Yanase skew information is bounded by the quantum Fisher information associated with the phase parameter. Besides, the quantum Cramér–Rao inequality is expressed in terms of skew information. Since these two fundamental quantities are based on the concept of quantum uncertainty, we derive here their analytical formulas for arbitrary two qubit X-states using the same analytical procedures. A comparison of these two informational quantifiers for two quasi-Werner states composed of two bipartite superposed coherent states is examined. Moreover, we investigated the decoherence effects on such quantities generated by the phase damping, depolarization and amplitude damping channels. We showed that decoherence strongly influences the quantum criteria during the evolution and these quantities exhibit similar dynamic behaviors. This current work is characterized by the fact that these two concepts play the same role and capture similar properties in quantum estimation protocols.