  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 X 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.
