Discrete photonic color entanglement and single-photon up-conversion

Abstract

The two main experiments explore and harness the fundamental properties of the largely unexplored photonic frequency degree of freedom(DOF) for the context of quantum information science. In first experiment we demonstrated an efficient source of ``discretely'' color-entangled photon-pair quantum states. We developed a detection method, based on two-photon interference, to quantify the entanglement generated by the source. Furthermore we showed that this could also be used to obtain a full tomographic reconstruction of the system's density matrix in color space. Qubit information was reliably encoded, transmitted and measured in a two-dimensional (discrete) subspace of the continuous photonic color DOF.<br />In the second experiment of this thesis, we explored the technical requirements for high-efficiency single-photon up-conversion (SPUC).<br />This technique, based on sum frequency generation in nonlinear media, coherently alters the frequency of light at the individual photon level.<br />It has not only been used for efficient photon counting in the infrared range, but it also holds the promise to perform local manipulations on the discrete color qubits generated and analyzed in the first part of this work. A test-bed system for SPUC was built, characterized and compared to theoretical models, in order to estimate the technology's performance in future quantum optics experiments.