Preparation Of Multi-qubit Entangled States Via Atomic Cavity QED

Quantum entanglement is one of the most striking and unimaginable feature for quantum physics differentiating from classical physics.Preparation and manipulation of quantum entangled states lies at the heart of the quantum information.Quantum entanglement play an important role and used widely as a principal resource in quantum teleportation,quantum dense coding, quantum key distribution,quantum computation,and so on.The process of performing quantum information can be regarded as the process of manipulation of entangled states.Quantum entanglement play a crucial role in testing the foundmental principles of quantum mechanies.Bipartite entangled states have been known very well by scientists and some of generation schemes have been proposed.However,multipartite entangled states are still under research. To investigate fully quantum entanglement is vital for both quantum theory and quantum information science.In this thesis,we focus our research on generation of atomic qubits entangled states via Cavity-QED.We propose a theoretical scheme to generate genuine entangled states of four atomic qubits in separated optical cavities using the atom-light interaction under the condition of the large detuning and single photon detections.We show that GESs of four atomic qubits can be produced deterministically.Starting with one prepared GES we have found the sixteen orthonormal and independent GESs.It is show that these sixteen GESs build a new type of representation the four-qubit system,the genuine entangled-state representation.This representation provides us with new interesting insight into better understanding multipartite entanglement.It is indicate that the GHZ state and W state,the cluster state,and the symmetric Dicke state for a four-qubit system can be explicitly expressed in terms of the sixteen GESs.We also consider the influence of the imperfection of photodetectors in the scheme,and indicated that the inefficiency of photodetectors does not affect the quality of the generated entangled states,but it decreases the success probability. We present a cavity-QED-based scheme to generate GHZ state and W state for multi-qubit atoms.The scheme makes use of linear optical devices and also has an ideal success probability of 100%.We utilize the N-type atomic off-resonant interaction with two classical fields and a single-photon source to realize the Hadamard operation and control phase operation.By controlling the interaction sequence and properly preparing the initial state of the atoms,we can easily produce entangled states of atomic qubits.