The single-photon transmission spectrum under symmetrical atom–photon couplings and 2θ = 2π (a), 2θ = π (b), 2θ = 0.4π (c) with Ω<sub>1</sub> = 0.9 Ω (left atom) and Ω<sub>2</sub> = 1.1 Ω (right atom) and Ω = 1.0

<p><strong>Figure 4.</strong> The single-photon transmission spectrum under symmetrical atom–photon couplings and 2θ = 2π (a), 2θ = π (b), 2θ = 0.4π (c) with Ω<sub>1</sub> = 0.9 Ω (left atom) and Ω<sub>2</sub> = 1.1 Ω (right atom) and Ω = 1.0. (d) The energy-level configuration of the Λ-type three-level atom. <em>V</em><sub>1</sub> = <em>g</em><sub>1</sub><sup>2</sup>/2 <em>v<sub>g</sub></em> = 0.2 and <em>V</em><sub>2</sub> = <em>g</em><sub>2</sub><sup>2</sup>/2 <em>v<sub>g</sub></em>. The coupling strengths <em>g</em><sub>1</sub> and <em>g</em><sub>2</sub> are in units of <em>V</em><sub>g</sub>.</p> <p><strong>Abstract</strong></p> <p>Based on the symmetric, asymmetric atom–photon couplings and the phase difference between two separated atoms, single-photon transport properties in an optical waveguide coupled with two separated two-level atoms are theoretically investigated. The transmission and reflection amplitudes for the single-photon propagation in such a hybrid system are deduced via a real-space approach. Several new phenomena such as phase-coupled induced transparency, single-photon switches, symmetric and asymmetric bifrequency photon attenuators are analyzed. In addition, the dissipation effect of such a hybrid system is also discussed.</p>