Requirement of system-reservoir bound states for entanglement protection

In this work, a genuine mechanism of entanglement protection of a two-qubit system interacting with a dissipative common reservoir is investigated. Based on the generating of bound state for the system-reservoir, we show that stronger bound state in the energy spectrum can be created by adding other non-interacting qubits into the reservoir. In the next step, it is found that obtaining higher degrees of boundedness in the energy spectrum leads to better protection of two-qubit entanglement against the dissipative noises. Also, it is figured out that the formation of bound state not only exclusively determines the long time entanglement protection, irrespective to the Markovian and non-Markovian dynamics, but also performs the task for reservoirs with different spectral densities.