Decoherence-free interaction and maximally entangled state generation in giant-atom semi-infinite waveguide systems

Giant atoms are artificial atoms that can couple to a waveguide non-locally. Previous works have shown that two giant atoms in a braided configuration can interact through one-dimensional (1D) infinite and chiral waveguides, with both individual and collective atomic relaxation being fully suppressed. In this paper, however, we show that the decoherence-free interaction (DFI) between two giant atoms can be realized in both braided and nested configurations when the waveguide is semi-infinite. This protected interaction fails to appear in semi-infinite waveguide systems containing two separate giant atoms or two small atoms. We also study the entanglement generation between two giant atoms coupled to a 1D semi-infinite waveguide. The results show that the maximally entangled state is generated in both braided and nested configurations due to the formation of DFI, and in the separate configuration, the maximally achievable entanglement can exceed 0.5. Finally, we generalize the discussion on DFI and entanglement generation to the case involving multiple giant atoms coupled into a semi-infinite waveguide. This study presents a new scheme for realizing DFI and generating maximally entangled states in giant-atom waveguide-QED systems.

💡 Research Summary

This paper investigates decoherence‑free interaction (DFI) and entanglement generation in waveguide quantum electrodynamics (QED) systems that incorporate giant atoms coupled non‑locally to a semi‑infinite one‑dimensional (1D) waveguide terminated by a perfect mirror. While previous studies demonstrated DFI for two giant atoms in braided configurations within infinite or chiral waveguides, the authors show that DFI can also be realized in both braided and nested configurations when the waveguide is semi‑infinite. The semi‑infinite geometry introduces an additional phase contribution from the mirror‑reflected photon path, leading to modified Lamb shifts, exchange couplings, and decay rates that depend not only on inter‑atom distances but also on each atom’s distance from the mirror.

The authors first derive a Markovian master equation for M two‑level giant atoms, each coupled at N_j points with individual coupling rates γ_{jn}. The resulting coefficients (δω_j, g_{jk}, Γ_j, Γ_{coll,jk}) contain terms proportional to sin