| The aim of this work is to explore the characterization of various entangled parameters of the two-photon state that is created in the process of spontaneous parametric down-conversion, as well as to investigate the potential application of these two-photon states to quantum communication and quantum information processing. The parameters fall into two natural divisions, the discrete-variable and continuous-variable regimes.; Polarization-correlated photon pairs are used to explore the discrete-variable regime. Using these polarization-correlated photon pairs we investigate phase-covariant quantum cloning, sum-variance entanglement measures, and unambiguous state-discrimination. Phase-covariant quantum cloning is experimentally demonstrated to provide higher cloning fidelity than a universal quantum cloner. The simplicity of the practical implementation of this cloning method makes this cloner a useful addition to the quantum information and communication toolbox. Next, it is experimentally demonstrated that three, concatenating, sum-variance entanglement measures possess higher sensitivities than the popular Bell entanglement measure, while each requires fewer measurements than a Bell measurement to obtain. Finally, it is demonstrated that unambiguous state-discrimination of nonorthogonal, bipartite entangled-states involves an analogous physical mechanism to that of entanglement distillation of bipartite entangled states. This physical mechanism is the basis of a two-qudit, three-party secret sharing protocol.; In the continuous variable regime, two-photon position-momentum entanglement and two-photon time-energy entanglement is explored. Entanglement between discrete regions of space (pixels) is demonstrated using transverse momentum and position entanglement. Each photon is mapped onto as many as six pixels, where each pixel represents one level of a qudit state. Next, the number of information eigenmodes K of time-energy entanglement is investigated. Explicit measurements estimate K to be greater than 100, with theoretical estimates predicting a value of as high as 1 x 10 6. Finally, a protocol for large alphabet quantum key distribution is presented that uses energy-time entangled biphotons. Binned, high-resolution timing measurements are used to generate a large alphabet key of up to 1278 characters, while the security of the quantum channel is determined from the measured visibility of Franson interference fringes. Successful encryption and decryption is demonstrated for a generated key of ∼5 bits per photon, with a key bit error rate of ∼10%. |
