The Research Of The Entanglement Degree Of Three-qubit States In The Quatum Clone

Quantum entanglement is one kind of significant resources about quantum information. In recent years, the study on the relationship between entanglement states clone scheme of entanglement degree and fidelity has become one of the main research directions, and it has already become a vital research topic about how to select the cloning project. In this paper, the studies found that the various cloning recovery process would affect the entanglement of the output state, theoretically. It showed that the entanglement degree directly reflects the entanglement relationship of the clone output state particle, which was a great important factor to determine whether the cloning program is best.This paper introduced the classification and main steps of quantum cloning, the required measurement and recovery of resources in cloning process, and theory in calculation. Then, studied two clone scheme was cloned approximatively about two qubit states and three-qubit states based on a single and double quantum channel, and its fidelity and entanglement degree was calculated. The main results were obtained as following three aspects:Firstly, the cloning program was proposed based on two quantum channels to unknown two-qubit entanglement. The main processes were that the sender to measure the quantum which was held on, the receiver to recover the quantum state through unitary transformation and quantum logic gate. Further, the fidelity and entanglement of cloning output were calculated and the changing image of entanglement degree on input and output states with unknown parameter was drawn.Based on the single quantum channel, the entanglement degree of two-qubit unknown entangled state of cloning output was calculated, and compared with the second quatum clone scheme.Secondly, based on the single quantum channel, it was researched and found that the entanglement degree of the quantum remote cloning input and output states for unknown three-qubits GHZ states. And then the changing image of entanglement degree with input and output states was drawn. The results illustrated that the proposed scheme was general when the quantum introduced logical gate was different in recovery period with the fidelity always be five sixths. Thus, the value of entanglement degree didn’t depend on the selected logical gates.Confirmed the scheme mentioned to be the general cloning scheme.Finally, the entanglement degrees for the above schemes of the quantum remote cloning input and output states for unknown three-qubits GHZ states were both calculated. And the difference was the selection of quantum logical gate. By calculation of the fidelity for output state, the range for fidelity value is [21/36,25/36], revealing the proposed schemes were both to be quatum cloning of constant phase. In addition, it was found that the entanglement degree of the output state was related to the logic gate. Furthermore, we studied the change curves of fidelity, entanglement degree of input and output stated with the variation of input state parameters. The advantages and disadvantages of single quantum channel and two quantum channel cloning schemes were discussed from different perspectives, providing theoretical basis for the further research on the scheme selection of entangled states.