Title: Deterministic photon sorting and its realization in waveguide QED systems

Abstract:

Sorting quantum fields into different modes according to their Fock-space quantum numbers is a highly desirable quantum operation. Recently, we develop a general theory for characterizing and optimizing such a nonlinear operation based on exact formulation and minimization of the error functional. In particular, we apply the theory to a passive waveguide QED system and find that a pair of two-level emitters, chirally coupled to a waveguide, may scatter single- and two-photon components of an input pulse into orthogonal temporal modes with a very high fidelity ≳ 0.9997.  Such a high fidelity is enabled by an interesting two-photon scattering dynamics: while the first emitter gives rise to a complex multimode field, the second emitter recombines the field amplitudes, and the net two-photon scattering induces a self-time reversal of the input pulse mode. The presented scheme can be employed to construct deterministic logic elements for propagating photons, such as a nonlinear-sign gate with a fidelity ≳ 0.9995.