Approximating Large Scale Arbitrary Unitaries with Integrated Multimode Interferometers

Unitary operations using linear optics have many applications within the quantum and neuromorphic space. In silicon photonics, using networks of simple beam splitters and phase shifters have proven sufficient to realize large-scale arbitrary unitaries. While this technique has shown success with high fidelity, the grid physically scales with an upper bound of O(n2). Consequently, we propose to considerably reduce the footprint by using multimode interference (MMI) devices. In this paper, we investigate the active control of these MMIs and their suitability for approximating traditionally used unitary circuits