Research On Preparation And Operation Of Multipartite Entangled States

Entanglement represents not only an important and peculiar property of quantum mechanics,but also a key resource in quantum information processing.In the beginning of this thesis,we review the basis of quantum entanglement and emphasize its importance.Then the recent theoretical and experimental progresses on multi-partite entanglement are introduced.Based on the description of optical quantum entangled systems,polarization entanglement,and elements of linear optical devices,the main scheme of entangled photon pair source is presented,via the spontaneous parametric down conversion process(SPDC).The maximally-entangled photon pair is generated via Sandwich-structured beam-like type-II SPDC process,with the maximal fidelity 99.15%.Based on high-fidelity Sandwich-type entanglement source,a simple and reliable method has been proposed for engineering a tunable Werner state and realized experimentally.The whole setup mainly includes a parametric down-conversion source and a controllable depolarization channel which consists of a Sagnac-like interferometer and some complete dephasing operations.The generated Werner states are characterized by quantum state tomography,and the fidelity is also over 99%.The parameter of Werner state can be tuned from 0 to 0.992.Due to the importance of multipartite quantum system for quantum computation and communication,we present an experimental generation of three-photon entangled states.The fidelity of our GHZ state was 87.25%.To verify the entanglement,the Mermin inequality is measured,up to 3.50 ± 0.05,which is much higher than 2,the classical bound.In addition,a class of GHZ-like states is generated to characterize the entanglement source.