Quantum Information Processing with Single Photons

Photons are natural carriers of quantum information due to their ease of distribution and long lifetime. This thesis concerns various related aspects of quantum information processing with single photons. Firstly, we demonstrate N -photon entanglement generation through a generalised N×N symmetric beam splitter known as the Bell multiport. A wide variety of 4-photon entangled states as well as the N -photon W-state can be generated with an unexpected non-monotonic decreasing probability of success with N . We also show how the same setup can be used to generate multiatom entanglement. A further study of multiports also leads us to a multiparticle generalisation of the Hong-Ou-Mandel dip which holds for all Bell multiports of even number of input ports. Next, we demonstrate a generalised linear optics based photon filter that has a constant success probability regardless of the number of photons involved. This filter has the highest reported success probability and is interferometrically robust. Finally, we demonstrate how repeat-until-success quantum computing can be performed with two distant nodes with unit success probability using only linear optics resource. We further show that using non-identical photon sources, robustness can still be achieved, an illustration of the nature and advantages of measurement-based quantum computation. A direct application to the same setup leads naturally to arbitrary multiphoton state generation on demand. Finally, we demonstrate how polarisation entanglement of photons can be detected from the emission of two atoms in a Young’s double-slit type experiment without linear optics, resulting in both atoms being also maximally entangled.