On-chip unitary generation of arbitrary complex spatial photonic states

The rapid advancement and high integration of photonic integrated circuits (PICs) have enabled energy-efficient and fast computation in compact chip designs. A fundamental challenge in both classical and quantum information processing is the ability to create light wavefronts with complex spatial amplitude and phase distributions. Traditional methods that involve splitting light into multiple channels and modulating each one individually typically lead to chip area and power waste. We introduce a compact programmable PIC capable of generating arbitrary complex spatial states in a power-conserving manner. The proposed system harnesses multipath interference in an interlaced arrangement of phase modulator arrays and photonic lattices to transform excitation from a single input channel to a multi-channel output state with the required amplitude and phase profile. For an N-port device, we demonstrate that two layers of N phase shifters can approximate arbitrary N-dimensional amplitude states with sufficient accuracy, while three layers allow complete control over both amplitude and phase. Furthermore, we experimentally demonstrate arbitrary state generation with a silicon photonic platform by utilizing a measurement-and-feedback setting for in situ programming of the device to optimize the desired output state. The present solution allows for a flexible design, compatible across various material platforms, for the integration of state generators used in future PICs that require arbitrarily complex inputs.