Chip-to-chip quantum photonic interconnect by path-polarization interconversion

Integrated photonics has enabled muchprogress towards quantum technologies. Many applications, e.g., quantum communication, sensing and distributed cloud quantum computing, require coherent photonic interconnection between separate on-chip subsystems. Large-scale quantum computing architectures and systems mayultimately require quantum interconnects to enable scaling beyond the limits of a single wafer and towards multi-chip systems.

However, coherently connecting separate chips remains a challenge, due to the fragility of entangled quantum states. Thedistribution and manipulation of entanglement between multiple integrated devices is one of the strictest requirements of these systems. Here, we report the first quantum photonicinterconnect, demonstrating high-fidelity entanglement distribution and manipulation between two separate photonic chips, implemented using state-of-the-art silicon photonics.
Path-entangled states are generated onone chip, and distributed to another chip by interconverting between path and polarization degrees of freedom via a two-dimensional grating coupler on each chip. This path-to-polarization conversion allows entangled quantum states to be coherently distributed. We use integrated state analyzers to confirm a Bell-type violation of S=2.638±0.039 between the two chips.With further improvements in loss, this quantum photonic interconnectwill providenew levels of flexibility in quantum systems andarchitectures.