# Symmetries and entanglement features of inner-mode resolved correlations of interfering nonidentical photons

## TL;DR

This paper demonstrates how inner-mode resolved measurements can restore and harness quantum interference among nonidentical photons, revealing symmetries and enabling entanglement in linear optical networks without additional filtering.

## Contribution

It introduces a method to use inner-mode quantum information to restore interference and generate multipartite entangled states with nonidentical photons in linear optical networks.

## Key findings

- Restores quantum interference between nonidentical photons without filtering.
- Reveals symmetries of multiphoton networks and states.
- Generates multipartite entangled states with fixed interferometers.

## Abstract

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. Here, we employ correlation measurements in the photonic inner modes, time or frequency, to restore quantum interference between photons differing in their colors or injection times in arbitrary linear optical networks, without the need for additional filtering or post selection. Interestingly, we demonstrate how harnessing the multiphoton inner-mode quantum information enables to unravel symmetries of multiphoton networks and states and the generation of an entire class of multipartite entangled states with a fixed interferometer. These results are therefore of profound interest for future applications of universal inner-mode resolved linear optics across fundamental science and quantum technologies with photons with experimentally different spectral properties.