A signal amplifier is provided via a triple Mach-Zehnder interferometer (MZI) apparatus for determining intensity distribution at either a first port or a second port by a photon from a source. The first and second ports correspond to respective first and second directions. The MZI apparatus includes four beam-splitters disposed co-linearly in parallel between the source and the ports, six parallel mirrors, and first and second path projectors. Three of these mirrors are displaced along the first direction from the beam-splitters, while the remaining mirrors are displaced along the second direction. The path projectors conduct weak measurement of a photon occupation number and are disposed between the second beam-splitter and an adjacent downstream mirror. The output port is disposed beyond the fourth beam-splitter in the first direction. The intensity distribution at the output port is positive in response to one of the first measurement being positive and the second measurement being negative.