| With the continuous development of quantum mechanics, a new field-quantum information science appeared in the 21st century. Quantum information theory is based on the superposition, non-locality, entanglement, no-cloning and other features of quantum mechanics, and it is the field that apply quantum mechanics on information science. Quantum information technology includes many aspects, especially the study of quantum communication has been researched more. And now quantum computer also sparked people's enthusiasm. So it has great scientific and academic value and potential commercial value.As a branch of quantum information science, quantum communication mainly focus on these areas, such as the quantum teleportation that unknown quantum states can be transmitted remotely without sending any particles; the quantum dense coding that through sending only one quantum bit transmit two bits of classical information; the quantum information splitting which transmit quantum information secretly by splitting a message into several parts and the quantum cloning that copy an unknown quantum state approximately or probabilistically. The study of these content is based on the physical systems:(1)optical system, (2)optical cavity quantum electrodynamics (cavity QED) system, (3)ion trap system, (4)nuclear magnetic resonance (NMR) system, (5)the superconductor system based on "Josephson", (6)quantum dot system. The difference between them is the information storage unit. Among them the cavity QED system's research experiense the longest time, and also have the most comprehensive theoretical development; Linear optical system is the most closely an experimental feasible system which combined with experiment and theory. They all caused the researchers'interest. This paper mainly proposes some schemes to implement quantum dense coding and quantum cloning in cavity QED and linear optical systems, which achieves the following results,1. Implementation for quantum dense coding of four particles cluster state in optical systemOur protocol is to implement dense coding of four-particle cluster state in linear optical system. We code on one particle and two particles, respectively. In this scheme, the photon is neutral particles, therefore, compared with other particles it has longer decoherence time with its surroundings. In experiments it is easy to realize single bit gate operation using linear optical element, so it is easily to achieve the photon coding operation. And with the non-destructive equivalent detector, polarization beam splitter and FS-PBS, cluster states can be completely distinguished. That is, successful probability of dense coding is equal to 1.2. Scheme to implement optimal symmetric universal and phase-covariant quantum cloning in optical systemIn one linear optical system, we can achieve to implement many kinds of quantum cloning machines by adjusting the parameters of each device in the same time. These cloning contain the optimal symmetric 1â†'2 universal, optimal symmetric 1â†'2 phase-covariant and optimal symmetric economical 1â†'3 phase-covariant quantum cloning. Take state of a polarization bits to clone to path bits. In the existing condition of experiment and technology, the scheme is feasible.3. Implementation for the optimal asymmetric economical 1â†'3 phase-covariant telecloning in cavity-QED systemWe propose a cavity QED scheme, which implement the optimal asymmetric economical 1â†'3 phase-covariant telecloning. Our protocol does not need other particles' assist. During the interactive process of atoms and cavities, we can ignore the interaction of cavity field states and the cavity decay. In the whole cloning process, cavity field is just in virtual inspire state, which can greatly extend the efficient decoherent time. Therefore, in a series of existing cavity QED technology, the scheme is feasible in the experiment. |
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