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

Abstract 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.