  We investigate the utility of parity detection to achieve Heisenberg-limited
phase estimation for optical interferometry. We consider the parity detection
with several input states that have been shown to exhibit sub shot-noise
interferometry with their respective detection schemes. We show that with
parity detection, all these states achieve the sub-shot noise limited phase
estimate. Thus making the parity detection a unified detection strategy for
quantum optical metrology. We also consider quantum states that are a
combination of a NOON states and a dual-Fock state, which gives a great deal of
freedom in the preparation of the input state, and is found to surpass the
shot-noise limit.
