Research On Quantum Entanglement Concentration

Quantum entanglement is an important resource in quantum communication and scalable quantum networks.Entangled states are widely used in quantum computation and quantum communication,but in the channel with ambient noise,the decoherence will inevitably occur,which will make the maximum entangled state into the partially entangled state.Entanglement concentration is a powerful tool to extract the maximum entangled state from the partially entangled state.Multi-photon entanglement states and microwave photon entanglement states are two kinds of very important qubits in quantum communication.They have strong anti-interference ability in the transmission process,but they are still affected by noise and lead to the reduction of entanglement degree.Therefore,it is an important and necessary task to study the entanglement concentration of these kinds of states.We study the entanglement concentration of multi-photon entanglement state and microwave photon entanglement state,and proposes the entanglement concentration scheme for six-photon cluster states,microwave photon W state and four-microwave photon cluster states in this paper.The major work of our paper is as follows.(1)Two entanglement concentration schemes of six-photon cluster states are proposed.In the first scheme,the appropriate POVM operators are found through calculation and applied to the corresponding particles to obtain the maximum entangled six-photon cluster states,and it can be extended to 2N photons;In the second scheme,the parity check device is constructed by cross-Kerr effect,and the entanglement is concentrated with the help of single qubit,and the final success probability is improved through repeated iterations.When Alice and Daniel iterated four times respectively,the success probability of obtaining the maximum entangled state exceeded to 87%.(2)Two entanglement concentration schemes for microwave photon entanglement states are proposed.The first one is the entanglement concentration of microwave photon W state.The entanglement concentration is accomplished by combining linear optical element with quantum non-demolition detection device;The second is the entanglement concentration of four-microwave photon cluster states.We use the auxiliary single qubit and quantum non-demolition detection device,and many CNOT gate operations to complete the entanglement concentration.