Realization Of The Quantum Cloning Machine Based On Spin-Chaine And Interaction-Free Measurement

The quantum no-cloning theorem prohibits an arbitrary quantum state from being copied perfectly because of the linearity of quantum mechanics. So a lot of attention has been paid to approximate cloning. In this dissertation, we propose several schemes for implementing quantum cloning based on quantum spin networks and interaction-free measurement. The dissertation includes the following results.(1) Due to the advantage of quantum spin networks that it can performs a free dynamical evolution without almost any external control, we propose a scheme to. implement 2â†'M phase-covariant quantum cloning machine by using a M+2 spin star network in which the two central spins interact with the M outer spins respectively. The effect of the magnetic field on the fidelity of the cloning is also investigated. By applying an external magnetic field on the spin system, the fidelity of the cloning machine can be largely improved.(2) A schemes of 1â†'2 economical phase-covariant quantum cloning machine (EPCCM) is proposed by using the interaction free measurement (IFM). Thanks to the imperfection of IFM gate, we constructed the quantum cloning machine with a simple quantum circuit and a very high probability of success compared to previous methods. We also find that even under the case that the interaction between a photon and an absorbing object is imperfect, we can still get a very high value of fidelity extremely closed to the optimal one, which is very important for experiment. The above results provide the reliable theoretical foundation for the quantum information, it has the theoretical guideline and important reference value for the reach of quantum cloning experiment.