Effects of linear modulation of qubits–resonator coupling on quantum entanglement in circuit QED

We investigate to efficiently maintain the quantum entanglement between qubits through linearly modulating the coupling coefficient between qubits and field in circuit quantum electrodynamics system. We find that the maintenance time of entanglement between coupling qubits is closely related with the modulation type. Compared to the case of constant coupling coefficients, the first disappearance of entanglement between qubits is largely delayed when the coupling coefficients are linearly modulated with a small ramp. However, it is unfavorable for the maintenance of entanglement even leads to fast disappearance if the coupling coefficients are modulated with a large slope. The disappearance time of entanglement not only relies on the quantum state of coupling qubits, but also depends on the average photon number. The more the average photon number is, the more disadvantageous quantum entanglement maintains.