We discuss the prospects of performing Heisenberg-limited quantum sensing and
metrology using a Mach-Zehnder interferometer with input states that are superpositions
of twin-Fock states and where photon number parity measurements are made on one of
the output beams of the interferometer. This study is motivated by the experimental
challenge of producing twin-Fock states on opposite sides of a beam splitter. We focus on
the use of the so-called pair coherent states for this purpose and discuss a possible
mechanism for generating them. We also discuss the prospect of using other superstitions
of twin-Fock states, for the purpose of interferometry.