Time-bin to Polarization Conversion of Ultrafast Photonic Qubits

The encoding of quantum information in photonic time-bin qubits is apt for long distance quantum communication schemes. In practice, due to technical constraints such as detector response time, or the speed with which co-polarized time-bins can be switched, other encodings, e.g. polarization, are often preferred for operations like state detection. Here, we present the conversion of qubits between polarization and time-bin encodings using a method that is based on an ultrafast optical Kerr shutter and attain efficiencies of 97% and an average fidelity of 0.827+/-0.003 with shutter speeds near 1 ps. Our demonstration delineates an essential requirement for the development of hybrid and high-rate optical quantum networks

Complete Characterization of Quantum Optical Processes with a Focus on Quantum Memory

This thesis introduces and implements a characterization procedure called coherent state quantum process tomography and applies it to a selection of quantum operations. The procedure holds advantages over previous quantum process tomography methods, a pri- mary one is that a process can be characterized by measuring its effect on a set of coherent states which are readily available from a laser source. After introduction of the characterization procedure, the method is tested on a simple process of an electro-optical modulator and polarizing beam splitter. The accuracy of the characterization is verified by comparison of the predicted action of the reconstructed process tensor versus the actual experiment involving a squeezed vacuum state. The algorithm is then implemented and verified on a quantum memory system based on electromagnetically induced transparency, a system that was previously shown capable of storing a squeezed vacuum state. Lastly, a new optical storage system based on a gradient echo memory scheme is con- structed and optimized to achieve memory retrieval efficiencies of >80%. To characterize this system, a modified coherent state quantum process tomography algorithm based on the method of maximum likelihood estimation is employed. Despite the high efficiency values, the presence of excess noise resulted in the degradation of the storage device per- formance to be below the benchmarks of a quantum memory system. This estimation algorithm is also successfully implemented on the non-deterministic processes of photon creation and annihilation