Nonclassical interference of photons lies at the heart of optical quantum information processing. Here,
we exploit tunable distinguishability to reveal the full spectrum of multiphoton nonclassical interference.
We investigate this in theory and experiment by controlling the delay times of three photons injected into an integrated interferometric network. We derive the entire coincidence landscape and identify transition
matrix immanants as ideally suited functions to describe the generalized case of input photons with
arbitrary distinguishability. We introduce a compact description by utilizing a natural basis that decouples
the input state from the interferometric network, thereby providing a useful tool for even larger photon
numbers.