Efficient single-photon frequency conversion via a giant three-level atom

The single-photon frequency conversion in a one-dimensional waveguide coupled to a giant three-level atom is investigated. The analytical expressions of the single-photon scattering spectra are derived via the real-space Hamiltonian. Numerical results show that high-efficiency frequency conversion of single photons can be achieved by controlling the atom-waveguide coupling due to the phase-dependent interference effect of the multiple point couplings of the giant atom, and the conversion efficiency can ideally reach unity. The conversion spectra in both the Markovian and non-Markovian regimes show that multiple staggered peaks and dips emerge due to the non-Markovian retardation effect, in contrast to a single peak and dip in the Markovian regime. The influence of dissipation on the fidelity of frequency conversion is also displayed, and it shows that the fidelity is not sensitive to dissipation.