Spectral correlations among interfering nonidentical photons in universal linear optics
Multiphoton quantum interference underpins fundamental tests of quantum mechanics and quantum technologies. Consequently, the detrimental effect of photon distinguishability in multiphoton interference experiments can be catastrophic. In this talk, we describe how accessing the spectral properties of an arbitrary number of photons initially distinguishable in their quantum states allows the scalable restoration of quantum interference in arbitrary linear optical networks, without the need for additional filtering or post selection. Even more interestingly, we show how harnessing the full spectra of multiphoton quantum information by frequency and time resolved correlation measurements enables the characterization of multiphoton networks and states, produces a wide variety of multipartite entanglement, and increases the possibilities to achieve quantum computational supremacy. Furthermore, the multiphoton interference techniques described here pave the way to a scaling-up of multiphoton interference experiments. These results are therefore of profound interest for future applications of universal spectrally resolved linear optics across fundamental science and quantum technologies with photons with experimentally different spectral properties.
 V. Tamma and S. Laibacher, Quantum Inf. Process. 15(3), 1241-1262 (2015)