Nonreciprocal transport at the few-photon level is important for integrated quantum optics and quantum information processing. Unlike conventional small atoms, giant atoms interact with a waveguide through multiple discrete coupling points, allowing photons to accumulate phases along different coupling paths. In this paper, we theoretically investigate few-photon diode effects in a one-dimensional waveguide chirally coupled to a dissipative giant atom. By solving the Schrödinger equation, we obtain analytical solutions for both single-photon and two-photon scattering processes. Our results show that the two-point coupling structure of the giant atom allows diode effects to occur in multiple frequency regions, rather than only near resonance. By tuning the distance $L$ between the two coupling points, one can modify the propagation phase and the interference condition. This provides a geometric way to control the operating frequency range of the diode effect. For the chiral coupling configuration considered here, the optimal diode performance is obtained when the atom-waveguide coupling rate $\mathrm{\Gamma }$ and the dissipation rate $\kappa$ satisfy $\mathrm{\Gamma }/\kappa =1$. The two-photon diode effect further shows a clear dependence on $\mathrm{\Gamma }/\kappa$. For $\mathrm{\Gamma }/\kappa \gg 1$, the nonreciprocal response mainly appears in the bound-state-dominated region. In contrast, for $\mathrm{\Gamma }/\kappa \ll 1$, the transport tends to become reciprocal. These results indicate that nonlocal giant-atom coupling, chiral coupling, and dissipation can work together to realize frequency-tunable few-photon nonreciprocal transport.

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• Quantum communication
• Quantum information processing
• Quantum information theory