Fast Feedforward for Integrated Quantum Photonics

The ability to perform conditional unitary operations on a quantum state based on the outcome of a previous measurement - a process known as feedforward - is critical to realising photonic quantum
technologies. Feedforward schemes typically involve single-photon detection, signal processing, and implementation of electronic logic to dynamically reconfigure photonic circuits. The primary challenge in implementing fast feedforward lies in the timing constraints imposed by the speed of light. Heralded photons must be held in long delay lines whilst detection and subsequent processing occurs, which leads to significant transmission losses. Furthermore, the limited availability of high-performance integrated single-photon detector arrays necessitates the use of fibre-coupled detectors, introducing additional losses from on- and off-chip coupling. This project aims to build upon and integrate various existing technologies, including bright, multiplexed photon sources, fast modulators, integrated superconducting nanowire single-photon detectors (SNSPDs), electronic interfacing, and delay lines. With the objective to improve the speed and efficiency of feedforward processes by interfacing these elements and refining specific aspects. The ultimate goal is to then apply these advances to conduct an experiment, potentially a quantum teleportation, with a high success rate.