In this thesis we will theoretically investigate three potentially useful physical systems, after
first developing the theoretical framework necessary for studying them. First, we will study
the multiphoton absorption properties of maximally path entangled number (N00N) states.
This is directly relevant to quantum lithography, and beating the Rayleigh diffraction limit.
Next, we will develop a new scheme for quantum interferometry: dubbed coherent-light
boosted super-sensitive quantum interferometry. Which has the potential to reach below
the shot noise limit for high photon fluxes, and requires no esoteric detection protocol,
or technological elements which have yet to be developed. Finally we propose a method
to perform parity detection on the output modes of a Mach-Zehnder interferometer that
has been fed with two-mode squeezed vacuum. This detection scheme relies on a double
homodyning technique, that makes intensity correlation measurements at a series of chosen
bias phases. Sub-Heisenberg sensitivity scaling is expected for this setup.