Engineered photonic lattices enable controlled quantum walks on chip
Researchers have demonstrated that integrated photonic waveguide lattices can be precisely engineered to control quantum walks, enabling continuous interference across entire structures and the on-chip generation of complex, non-classical light states.
The study compares linear photonic circuits, where photons are injected externally, with nonlinear lattices that generate entangled photon pairs directly within the chip using materials such as aluminium gallium arsenide and lithium niobate. These platforms enable compact and scalable photonic integrated circuits (PICs) for quantum applications.
By carefully designing the waveguide geometry and tuning the coupling between lattice sites, the team was able to control the depth and behaviour of quantum walks, observing the gradual emergence of non-classical interference patterns.
The experiments show that nonlinear lattices, which generate photon pairs internally, can be interpreted as coherent superpositions of multiple linear quantum walks, providing insight into the underlying dynamics of photon propagation and entanglement on a chip.
The researchers also applied an inverse-design approach to create aperiodic lattices with optimised coupling profiles, achieving maximally entangled states such as the biphoton W-state.
These findings demonstrate that engineered photonic lattices can support high-dimensional entanglement and continuous photon interference, paving the way for advanced quantum state generation and manipulation in integrated devices. Characterisation techniques, including Hong–Ou–Mandel interference, coincidence counting, and quantum state tomography, confirmed the high quality and indistinguishability of the generated photons.
Looking forward, the team envisions hybrid PIC architectures that integrate linear and nonlinear sections on a single chip, allowing dynamic control of photon generation and quantum state evolution. Such devices could enable fully integrated quantum circuits for information processing, simulation, and communication, offering a compact and scalable route to practical quantum technologies. This work highlights the growing potential of integrated photonic lattices as a foundation for next-generation quantum photonic systems.
