Deterministic Entanglement Purification Of W Polarization State In Multiple Degrees Of Freedom With Hyper-Entanglement

Abstract:Entangled states as a kind of physical resources play an important role in the various aspects of quantum information, such as quantum teleportation, quantum key distribution, quantum computation and so on. However, restricted by experimental conditions and inevitable environmental noise, the entangled states prepared are not the maximally entangled states. Therefore, we must take entanglement purification to convert an ensemble of non-maximally entangled states into the maximally entangled states in order to achieve better effect of quantum communication and quantum computing. People have carried out extensive entanglement purification researches for the Bell state and GHZ state, but for W entangled state with higher fidelity, entanglement purification research is still in the exploratory stage.In order to solve the entanglement purification problem of W state, the thesis puts forward three kinds of deterministic, efficient and feasible entanglement purification scheme to get the high brightness and quality maximally entangled W state. In the schemes, three parties can obtain the maximally polarization W entangled state from the multiple degrees of freedom of hyper-entanglement W state, and it only requires the system entangled on the spatial degree of freedom but the polarization degree of freedom not be entangled at the same time. Firstly, two W polarization state entanglement purification schemes are introduced based on PBS: one exploits the current linear optical technology which is easy to implement in the experiment; the other is cross Kerr nonlinear technology which doesn’t need sophisticated single-photon detectors to measure the number of photons. Two schemes both can achieve efficient entanglement information in multiple degrees of freedom, but only consider the purification on a degree of freedom. Secondly, by improving the above scheme, this thesis proposes a W-HES state entanglement purification scheme based on the quantum repeater. The quantum repeater is not only can improve the fidelity of W state but also can increase the amplitude of coherent state. At the same time, it analyzes and processes the three possible errors existed in the hybrid system in noise channel: bit-flip errors, phase-flip errors and photons loss errors of the coherent state. Finally, it concludes that the presented scheme has the very big enhancement on fidelity by analyzing and comparing its performance.In conclusion, the deterministic polarization entanglement purification of W state in multiple degrees of freedom with hyper-entanglement can get high fidelity W state, the optimal solution can improve the amplitude of coherent state in consuming less information resources, which has great practical application values for quantum communication networks.15figures,2tables,71references.