  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.
