Multi-Photon Fock State Generation via Selective Single Photon Subtraction in a Cascaded Waveguide QED System

This work presents a deterministic photon subtraction scheme that selectively extracts photons from an input light stream based on their arrival time sequence. The scheme exploits the temporal entanglement generated during single-photon Raman interaction in a chiral waveguide coupled to a cascade of Λ-type atoms. It is demonstrated that this photon subtractor enables the generation of high-fidelity and modal purity multi-photon Fock states. Using a variational approach, the modal structure of the output light is identified, based on a non-orthogonal basis formed through post-selection of the output pulses. Within an input-output network framework, numerical simulations are performed to calculate the quantum state of the output light. Additionally, the use of the generated Fock-state pulses in optical interferometry is investigated, demonstrating their potential for quantum metrology applications at the Heisenberg limit.