In the quantum world, a single particle can have various degrees of freedom to encode quantum information. Controlling multiple degrees of freedom simultaneously is necessary to describe a particle fully and, therefore, to use it more efficiently. Here we introduce the transverse waveguide-mode degree of freedom to quantum photonic integrated circuits, and demonstrate the coherent conversion of a photonic quantum state between path, polarization and transverse waveguide-mode degrees of freedom on a single chip. The preservation of quantum coherence in these conversion processes is proven by single-photon and two-photon quantum interference using a fibre beam splitter or on-chip beam splitters. These results provide us with the ability to control and convert multiple degrees of freedom of photons for quantum photonic integrated circuit-based quantum information process.
@article{arxiv.1601.06250,
title = {On-chip coherent conversion of photonic quantum signals between different degrees of freedom},
author = {Lan-Tian Feng and Ming Zhang and Zhi-Yuan Zhou and Ming Li and Xiao Xiong and Le Yu and Bao-Sen Shi and Guo-Ping Guo and Dao-Xin Dai and Xi-Feng Ren and Guang-Can Guo},
journal= {arXiv preprint arXiv:1601.06250},
year = {2016}
}