Studies On Remote State Preparation In Dissipative Environments

In general,the quantum system is not closed and unavoidably interacts with its external noisy environments,causing decoherence of the quantum channel.In quantum communication process,this results in a deviation between the quantum state the sender wants to transmit and the quantum state the receiver actually receives.Thus,it is a significant subject to explore effective quantum communication protocol and enhance the efficiency of the transmission process in noisy environments.In this thesis,we firstly investigate the bidirectional controlled remote preparation of an arbitrary single-qubit state in the presence of dissipative environments with Lorentzian spectral density by using two EPR states as the entanglement source.We construct the quantum circuit of our scheme by means of unitary matrix decomposition procedure,then the effects of the Markovian and nonMarkovian environmental noises acting on the EPR states are analyzed through the analytical derivation and numerical calculations of the corresponding average fidelity.Moreover,we adopt two methods of weak measurement reversal and detuning modulation to improve the average fidelity.Our results show that the average fidelity can be remarkably enhanced under appropriate conditions of the WMR strength and the detuning.It is also shown that the two methods for fidelity improvement are more efficient in non-Markovian regime than in Markovian regime.On the other hand,we also investigate the average fidelity evolution behavior in dissipative environments with Ohmic spectral density.In this kind of noisy environment,it is found that even when the coupling strength between the system and environment is weak,the non-Markovian effect of the environment also exists.If the values of coupling strength and cut-off frequency are large enough,a stable bound state will be formed between the system and the environment,and the average fidelity will eventually decay to a value slightly larger than the original stable value,which is different from the behavior in dissipative environments with Lorentzian spectral density.The average fidelity can be further improved by applying weak measurement reversal operation of appropriate strength.Therefore the efficiency of remote state preparation can be continuously improved by adjusting Ohmic reservoir parameters in combination with the optimal weak measurement reversal operation.