| Quantum information is an advanced research topic in modern science and technology. The fresh subject devotes to exploit the fundamental principle of quantum mechanics and the wonderful characteristic of quantum state, such as quantum entanglement, squeezing, superposition etc, to perform the processing, computation and transmission of information. Utilizing entanglement, we can implement the disembodied transport of an unknown quantum state from one place to another remote place with high-fidelity, i.e. quantum teleportation. Via entanglement, we can also improve the channel capacity of classical signal in quantum channel, i.e. quantum dense coding, even we can entangle two quantum systems that have never directly interacted with each other by means of entanglement swapping. Researchers have applied the fundamental properties of quantum theory to cryptography. Quantum cryptography based on quantum mechanics can ensure absolute security of communication in principle. Quantum entanglement shared by more than two particles or parties is the essential base for developing quantum communication networks. Using the multipartite entanglement the novel telecloning, controlled dense coding, sharing secure quantum states and reduction of communication complexity can be realized. Quantum information was originally investigated with the discrete variables (dv) and was recently extended to the continuous variables (cv) system in the infinite dimension Hilbert space. The cv quantum communication has attracted wide interest due to the potential advantages such as high bit transmission rate. However, with the comparison to the dv system, the experimental investigation of cv quantum communication is relatively lagging. During my PhD study, our group completed the experimental and theoretical investigations on cv quantum dense coding, generation of multipartite entangled state of optical modes and controlled dense coding quantum communication.Following five parts will be presented in this thesis:1. Two kinds of bright EPR entangled beams were experimentally generated by means of nondegenerate optical parametric amplifier (NOPA). When the NOPA was operated at amplification, the EPR states with amplitude-quadrature correlation and phase-quadrature anticorrelation were generated firstly in 1999. The product of the amplitude and phase quadrature correlation degrees was 0.727±0.004<1; after the laser source was reconstructed, the EPR beams with amplitude-quadrature anticorrelation and phase quadrature correlation were obtained in 2001 and the product of the correlation degrees was 0.332±0.003 when the NOPA was operated at deamplification.2. The unconditional dense coding for continuous variables (cv) was experimentally realized using the high quality bright EPR beams in which a comparatively straight decoding technique, the direct detection of Bell state, was applied. The experiments demonstrated that the channel capacity of classical modulation signals can be improved due to exploiting quantum entanglement. The channel capacity achieved in our experiments was better than that of the dual homodyne coherent state, homodyne coherent state and squeezed state communication when the average photon number exceed 0.99,1.11 and 2.06 respectively. It is more interesting that we found in the experiment, that the maximum channel capacity for a single mode -Fock state communication can be surpassed with our system when the average photon number exceed 11.302.3. The fully inseparable bright tripartite entangled state (TES) was experimentally generated using the NOPA at deamplification and the linear optical system consisting of polarization beam splitters and half wave plates. The variances of the sum of the amplitudequadratures of the three obtained optical modes and the relative phase quadratures among them is respectively 3.28 dBm and 3.18 dBm below the corresponding Shot Noise Limit. The values of the left-hand-sides of the three inequalities in the inseparability criteria are 1.90, 1.83 and 2.94, respective...
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