Frequency tunable single photon diode based on giant atom coupling to a waveguide.

The single photon scattering properties in a waveguide coupling to a giant atom with a three-level system are investigated theoretically. One of the transitions of the giant atom couples to the waveguide at two points while the other one is driven by a classical field. Using the analytical expressions of the single photon scattering amplitudes, the conditions for realizing perfect single photon nonreciprocal scattering are discussed in both Markovian regime and non-Markovian regime.

Quantum correlation propagation in a waveguide-QED system with long-range interaction.

We investigate the excitation and correlation propagations among a one-dimensional atom chain with exponentially decaying, ideal long-range, and power-law decaying interactions. We show that although a clear light-cone-like structure can appear in both the excitation and correlation propagation patterns under the exponentially decaying interaction, only an obscure light-cone-like structure appears with multi-power-law decaying interaction and surprisingly an inverse light-cone-like structure appears in the ideal long-range interaction case. The extracted excitation and correlation propagation velocities in the ideal long-range interaction case are about one order of magnitude larger than those in the multi-power-law interaction case and about two orders of magnitude larger than those in the short-range interaction case.

Coherent frequency down-conversions and entanglement generation in a Sagnac interferometer.

A waveguide loop coupled to two external line waveguides by a 50/50 beam splitter forms a Sagnac interferometer. We consider the situation where two Λ-type three-level emitters are symmetrically coupled to the loop of a Sagnac interferometer and a single photon is input through one end of the line waveguides. Since the incoming photon is always in a superposition of the clockwise and counterclockwise modes of the loop and the two emitters are positioned symmetrically with respect to the input port of photon, the processes of photon scattering at the two emitters are symmetric and coherent.