The Research Of High Efficiency Parametric Down Conversion Entanglement Source And Its Application

Parametric down-conversion entangled sources have an irreplaceable role in linear optical systems,which can be cascaded for building large-scale optical quantum circuits.Improving the quality of entangled sources has always been an urgent problem to be solved.The main reason for the low collection efficiency of the previous parametric down-conversion source is that narrow-band filters are needed to eliminate the frequency correlation.In this paper,we optimize the parameters of the parametric down-converted crystal to find a parameter with no frequency correlation in which the collection efficiency and brightness are both optimal,and in order to be able to apply it to quantum communication,the wavelengths of parametric photons are set at communication band due to the lowest fiber loss.In the end,we obtain a high quality entangled source with a purity of 0.99 and a collection efficiency of 0.97.With the help of this entangled source,we implemented the following research work:1.A twelve-photon GHZ state is achieved.The photonic GHZ state can be used to demonstrate a large number of quantum circuits due to its strong optical coupling characteristics.As an auxiliary resource,it can also be used to implement multi-party quantum communication.2.High efficiency photon random boson sampling is achieved.By solving the problems which are difficult for an classical computer,designing the quantum circuit to solve and completely defeat the classical algorithm greatly reflects the superiority of quantum mechanics.3.The preparation of high-efficiency long-distance heralding entangled states is realized.The heralding high-efficiency entangled state can overcome the transmission loss at an entangled source distribution process,and truly realize the shared deterministic entanglement between the two places,which can be used as a resource to realize deterministic quantum computing.4.A lossless quantum teleportation is achieved.In the traditional quantum teleportation experiment,the success rate of quantum teleportation is lower than transmitting a photon directly since the channel loss can not be overcome.To achieve a lossless quantum teleportation allows a quantum teleportation process to be realized efficiently.