Protecting multipartite entanglement against weak-measurement-induced amplitude damping by local unitary operations

Protecting entanglement from decoherence has attracted more and more attention recently. Amplitude damping is a typical decoherence mechanism. If we detect the environment to guarantee no excitation escapes from the system, the amplitude damping is modified into a weak measurement of the system state. In this paper, based on local pulse series, we propose a scheme for protecting tripartite entanglement against decaying caused by weak-measurement-induced damping. Unlike previous bipartite state protection schemes, we consider three different situations: A series of unitary operations are applied on all of the three qubits, on two of the three qubits, and on only one qubit. The results show that this protocol can protect remote tripartite entanglement with a wide range of unitary operations. For the case of GHZ state, when the uniform pulses are applied on all qubits or on two qubits, the tripartite entanglement can be fixed around the entanglement of the initial state. Moreover, in the W state case, if a train of uniform pulses is applied on two qubits, we can see that the bipartite entanglement can be enhanced to the maximum with the third qubit being traced out. We also generalize our scheme to the cases of the superposition and mixture of GHZ and W states, and the numerical simulation shows that our protection scheme still works fine. The most distinct advantage of this entanglement protection scheme is that there is no need for the users to synchronize their operations. The fluctuations of the time interval between two adjacent local unitary operations, the operation parameters, and the pulse duration are all taken into consideration. All these advantages suggest that our scheme is much simpler and feasible, which may warrant its experimental realization.