Multi-photon Entangled States Prepared Linear Optical Realization

Entangled states plays a very important role in the research of QuantumInformation Processing (QIP). As to the research of fundamental theory, it mostvividly shows us the unique and wonderful nonlocality of quantum mechanics.Moreover, it is a kind of basic resource for applied prospects of quantumcommunication and quantum computation. A lot of research works have shown usthat it was the entangled states together with the coherence, which ensured manyquantum communication and quantum computation processes to be far more effectivethan their classic counterparts. So, people have make great efforts, trying to realize thepreparation of entangled states and other logic operations on different physicalsystems. One of those systems, linear optical system, has relatively clearer characterof entanglement and coherence, and is relatively easier to be operated, hence hasconsiderable feasibility. Therefore, we brought out a scheme of the preparation ofmulti-photon entangled states on the linear optical system.In this paper, basing on the scheme of the realization of control-not logic gate onthe linear optical system, we found out that the general photon polarization-entangledstate is equivalent to a special kind of photon path-entangled state. Using thisequivalence, we brought out a scheme of conditional preparation of multi-photonentangled states with single-photon sources, linear optical elements and photonnumber detectors. We proved that this scheme was universal (That is, we can preparemulti-photon entangled states of any dimension with a certain probability in theory)and provided a run-of-mill formula about it. We also calculated the scaling rule of thesources that the scheme needed and the success probability, then concluded that thisscheme was more effective than current experimental result, and could be realized bycurrent technology.