A scheme for fully programmable linear quantum networks based on frequency conversion

Abstract: Linear optical quantum networks, consisting of a quantum input state and a multi-port interferometer, are an important building block for many quantum technological concepts, e.g., Gaussian boson sampling. Here, we propose the implementation of such networks based on frequency conversion by utilising a so called multi-output quantum pulse gate (mQPG). This approach allows the resource efficient and therefore scalable implementation of frequency-bin based, fully programmable interferometers in a single spatial and polarization mode. Quantum input states for this network can be provided by utilising the strong frequency entanglement of a type-0 parametric down conversion (PDC) source. Here, we develop a theoretical framework to describe linear networks based on a mQPG and PDC and utilize it to investigate the limits and scalabilty of our approach.