Preparation Of Four-photon ?-type Entangled States And Its Distribution Over A Collective-noise Channel

Entanglement plays an important role in quantum information processing,mainly including quantum computation and quantum communication.The preparation of entangled states is an important aspect of quantum entanglement.The preparation methods of some special quantum entangled states are quite mature,such as the preparation of the four qubits GHZ,W,Cluster and Dicke states.In this paper,we mainly study the preparation of a four-photon ?-type entangled state by Kerr nonlinear medium and deterministic distribution of four-photon ?-type entangled state over an arbitrary collective-noise channel with cross-Kerr nonlinearity.In the first chapter,we mainly introduce the basic concepts of the quantum entanglement,quantum logic gates and related optics elements.In the second chapter,we present a preparation scheme of four-photon ?-type entangled state.The schematic of the scheme comprises simple optical elements.By using a polarization entanglement gate,these photons can overcome the influence of the collective-noise via cross-Kerr nonlinear.In the following,the state is collapsed to the final ideal quantum state with X homodyne measurement,and finally the four-photon ?-type entangled state is obtained.In the third chapter,we present a deterministic quantum entanglement distribution protocol for a four-photon ?-type polarization entangled state over an arbitrary collective-noise channel.This protocol adopts the X homodyne measurement based on the cross-Kerr nonlinearity to complete the task of the single-photon detection with nearly unit probability in principle.After the photons shared by the four receivers,they add some local unitary operations to obtain a standard four-photon ?-type polarization entangled state.