  Integrated photonics has enabled much progress towards quantum technologies.
Many applications, including quantum communication, sensing, and distributed
and cloud quantum computing, will require coherent photonic interconnection
between separate chip-based sub-systems. Large-scale quantum computing systems
and architectures may ultimately require quantum interconnects to enable
scaling beyond the limits of a single wafer and towards "multi-chip" systems.
However, coherently interconnecting separate chips is challenging due to the
fragility of these quantum states and the demanding challenges of transmitting
photons in at least two media within a single coherent system. Distribution and
manipulation of qubit entanglement between multiple devices is one of the most
stringent requirements of the interconnected system. Here, we report a quantum
photonic interconnect demonstrating high-fidelity entanglement distribution and
manipulation between two separate chips, implemented using state-of-the-art
silicon photonics. Path-entangled states are generated and manipulated on-chip,
and distributed between the chips by interconverting between path-encoding and
polarisation-encoding. We use integrated state analysers to confirm a Bell-type
violation of $S$=2.638+-0.039 between two chips. With improvements in loss,
this quantum interconnect will provide new levels of flexible systems and
architectures for quantum technologies.
