Manipulating quantum coherence of charge states in interacting double-dot Aharonov-Bohm interferometers

We investigate the dynamics of charge--states coherence in a degenerate double--dot Aharonov--Bohm interferometer with finite interdot Coulomb interactions. The quantum coherence of the charge states is found to be sensitive to the transport setup configurations, involving both the single--electron impurity channels and the Coulomb--assisted ones. We numerically demonstrate the emergence of a complete coherence between the two charge states, with the relative phase being continuously controllable through the magnetic flux. Remarkably, a fully coherent charge qubit arises at the double--dots electron pair tunneling resonance condition, where the chemical potential of one electrode is tuned at the center between a single--electron impurity channel and the related Coulomb--assisted channel. This pure quantum state of charge qubit could be \emph{experimentally located} at the current--voltage characteristic turnover position, where differential conductance sign changes. We further elaborate the underlying mechanism for both the real--time and the stationary charge--states coherences in the double--dot systems of study.