On-chip coherent conversion of photonic quantum signals between different degrees of freedom

TL;DR

This paper demonstrates on-chip coherent conversion of quantum photonic states between path, polarization, and transverse waveguide-mode degrees of freedom, enabling more efficient quantum information processing.

Contribution

It introduces the transverse waveguide-mode degree of freedom and shows coherent conversion between multiple degrees of freedom on a single chip.

Findings

Quantum coherence is preserved during conversion.

Successful conversion demonstrated with single-photon and two-photon interference.

Enables control of multiple photon degrees of freedom for quantum circuits.

Abstract

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.