Preparation And Conversions Of The Multi-qubit Quantum Entanglement

Knill–Laflamme–Milburn(KLM)Entanglement is proposed originally to decrease the error rate of linear optics quantum computation and increase the efficiency.In this thesis,photonic polarized multi-qubit KLM entangled state is generated via the weak cross-Kerr nonlinearity.The qubits are encoded on photonic polarizations(Vertical and Horizontal).X and P homodyne measurements are discussed to realize the Quantum Non Demolition Measurement.Besides,since KLM entangled state has the similar robustness against photon loss with W entangled state,we studied the mutual conversions between these two entanglements.As two distinct multi-qubit entanglements,it is reported W and GHZ entangled states cannot be converted to each other by local and operations classical communication.But recent works show that their conversions could be realized via the stochastic local operations and classical communication,or dissipation process,etc.Considering the attention paid to them,we further studied the mutual conversions between KLM and W entangled states.With the iteration utilization of the remaining photons,the schemes of KLM entangled state preparation and mutual conversions have high utilization ratios of photons.Through comparing among the KLM,GHZ and W entangled states,we consider the KLM entangled state contains format of GHZ entangled state and has the similar robustness to W entangled state.Thus the thesis guesses the KLM entangled state may be seen as the “compound” of GHZ entangled state and W entangled state.Based on this guess,the conversion of KLM state to W state or GHZ state may be easier to be understood.It can be helpful to study the relationship among these entanglements and the applications based on them.