Entanglement generation across exceptional points in two-qubit open quantum system -- the role of initial states

Abstract

We study an open quantum system of two qubits that are coupled by swapping interaction. Using the coupling strength between the qubits as a time scale, the Liouvillian of the system has exceptional points that depend on the disparity between the decay rates of the qubits. We find that the configuration of the initial states plays an important role in deciding the character of the entanglement dynamics at the initial stage of evolution. Depending on whether or not the initial excitations of the qubits can be swapped by the interaction that couples them, a change in the total decay rate can be either consistently unfavorable to entanglement generation, or shift the dynamics from hindering to enhancing entanglement generation, or vice versa, as the system traverses the exceptional points. The shift could also occur in a wide range of mixed states. We clarify the origin of the behavior in this work.