A new concept for design of photonic integrated circuits with the ultimate density and low loss

We challenge the current thinking and approach to the design of photonic integrated circuits (PICs) for applications in communications, quantum information and sensing. The standard PICs are based on directional couplers, that provide a wide range of functionalities but do not fully respond to the major technological challenges: massive parallelisation of transmission channels, low-energy dissipation and small footprint. We propose a new concept for design of PICs with the ultimate downscaling capability, the absence of geometric loss and a high-fidelity throughput. This is achieved by a periodic continuous-time quantum walk of photons through waveguide arrays that leverages on the simple and effective algebraic approach to engineering waveguide couplings. We demonstrate the potential of the new concept by reconsidering the design of basic building blocks of the information and sensing systems: interconnects, multiport couplers, entanglement generators and interferometers. An extensive feasibility check in dielectric and semiconductor fabrication platforms confirmed this potential.