Remote Transfer Of Gaussian Quantum Discord

Quantum information is a new and one of the forefront of scientific research subject, which is a combination of quantum mechanics, computer science and information science. It mainly studies how to use the basic principle of quantum mechanics and the characteristics of quantum state to complete the processing of information. Quantum entanglement is one of the important quantum resource for implementing quantum information processing. A series of tasks which can not be accomplished in classical world can be completed using quantum entanglement, for example:quantum dense coding, where the classical information can be transferred between two communicators with a high channel capacity, can be accomplished using quantum entanglement as quantum resource; quantum teleportation, where one can transfer an unknown quantum state remotely, can be completed using quantum entanglement as quantum resource; quantum entanglement swapping, where one can produce entanglement in the case of no direct interaction on the quantum system which is originally not entangled, can also be accomplished using quantum entanglement as quantum resource.As a precious resource in quantum information and quantum computation, quantum correlation has been widely concerned in the past ten years. It has been shown that quantum discord can describe the non-classical quantum correlation compared with quantum entanglement more generally in recent researches. Some quantum information tasks can be accomplished by using quantum correlation without quantum entanglement, such as single quantum bit quantum computation, quantum key distribution and so on. Our research mainly concentrated on completing the feasible quantum information tasks with quantum correlation. For example, whether two quantum states which have no direct interactions can be correlated by means of remote transfer? The answer is yes, this is what we discussed in the thesis.We propose a scheme realizing the remote transfer of Gaussian quantum discord, in which another quantum discordant state or an Einstein-Podolsky--Rosen entangled state serves as ancillary state. The calculation shows that two independent optical modes that without direct interaction become quantum correlated after the transfer. The output Gaussian quantum discord can be higher than the initial Gaussian quantum discord when optimal gain of the classical channel and the ancillary state are chosen. The physical reason for this result comes from the fact that the quantum discord of an asymmetric Gaussian quantum discordant state can be higher than that of a symmetric one, at certain conditions.The structure of the paper is as follows. We briefly review the development of quantum information and the research background of quantum correlation in the first chapter. We introduce the related theory of quantum entanglement and quantum correlation in the second chapter. The notation of quantum entanglement and quantum correlation are introduced, and the classification, criteria and experimental progress of quantum correlation are shown in this chapter. We present the Gaussian quantum discord remote transmission scheme in the third chapter. The dependence of output quantum discord on quantum discording noise, the compression parameter and the gain factor are discussed when quantum discord state and EPR entangled state respectively as the ancillary state. We find that the quantum discord of asymmetric Gaussian quantum discord states is higher than that of a symmetric one, at certain condition. The feasibility of quantum dense coding with Gaussian discord is discussed in the fourth chapter. We introduce the development and some related experiments of quantum dense coding firstly. Then, the characteristic and the channel capacity of continuous variable dense coding are elaborated. Finally, we analyze the channel capacity of quantum dense coding by using Gaussian quantum discord as the resource, which is same to that of quantum dense coding with a coherent state. In the fifth chapter, we summarize the thesis. The development and potential application of quantum discord are discussed. The facing problems in the development of quantum discord are also analyzed in this chapter.