Nonlocal Bell-state Measurement And Quantum Information Transfer Based On Cross-kerr Nonlinearity

Quantum Information Processing (QIP) enables the implementation of certain communication and computation tasks that are unavailable with traditional tech-nology. Bell-state measurement is an important operation, it is the key steps in QIP such as quantum teleportation, quantum dense coding, quantum error correc-tion, and so on. Especially, nondestructive Bell-state measurement can efficiently distinguish the four Bell states, simultaneously without destroying entanglement re-sources, which is important for the practical quantum communication and quantum computation. In recent years, photons of suffering low decoherence are ideal infor-mation carriers for long distance quantum communication, so optical QIP holds huge attraction. Traditional QIP tasks are completed by participants to share entangled states and then carry out local operations respectively. But in practical quantum communication and remote quantum computation, the transmission of single photon qubit would inevitably be disturbed by the environment, thereby affecting the effi-ciency of QIP. If we can realize the qubit nonlocal operations, it is not necessary for participants to share entangled resources and the errors in single photon transmis-sion can be avoided in certain QIP. So the study of nonlocal quantum measurement has important significance.This dissertation studies a nearly deterministic nonlocal Bell-state measure-ment. In the scheme, with the help of weak cross-Kerr nonlinearities medium, we realize the regulation of the interaction between signal photons using two intense coherent lights as communication "buses", and the two photons are located in dif-ferent places. The cross-Kerr nonlinearities medium makes the coherent light obtain a phase shift when the bunch of coherent light and a signal photon passing through it together. So in the scheme, after a series of quantum operations we set up, the quantum state information of signal photons will be displayed in the phase shift of the coherent light. Then we could determine the information of the signal pho-tons by measuring on the coherent light. In the present scheme, we can obtain the information of the signal photons without measuring on them, so the scheme is nondestructive. And when measurements are carried out on the two coherent lights, we use the photon number resolving detection with a much lower error rate, which makes our scheme nearly deterministic. Furthermore, compared to previous nonlo-cal Bell-state measurement schemes, our work does not require hyper-entanglement or classic communication, which makes the actual experimental operations easier. Soon afterwards, based on the nonlocal Bell-state measurement scheme, we study the quantum state information transfer process for single photon state and two pho-tons entangled state. Here the photons encoded the initial information and the photons received the infirmation finally are spatially separated. Analysis derives that the process of single photon state transfer is slightly different from conven-tional teleportation, but could be regard as a novel form of teleportation without entangled channel and classic communication. Two photons entangled state infor-mation transfer is more complex, which needs a local Bell-state measurement after the nonlocal Bell-state measurement. All the logic operations required in the whole process are feasible under the current experimental conditions...