A Universal Topological Platform for Nonreciprocal Spin-Photon Interface in Solid-State Quantum Networks
Fang-Yu Hong
A fundamental obstacle to scalable solid-state quantum networks is the lack of a universal interface providing strong light-matter coupling, deterministic nonreciprocal photon routing, and efficient extraction. Here we propose a plasmonic platform overcoming these challenges using a Tomonaga-Luttinger liquid (TLL) in a single-walled carbon nanotube (SWCNT) microtoroid. The TLL's collective bosonic excitations are kinematically protected against backscattering by a large valley-momentum mismatch, guaranteeing robust chiral spin-momentum locking unattainable in dielectric cavities. This 1D protection enables deterministic routing of circularly polarized photons from a quantum emitter (e.g., a nitrogen-vacancy center) into distinct propagation channels. By aligning the emitter's symmetry axis, parasitic π transitions are geometrically forbidden. Furthermore, residual atomic-scale backscattering is suppressed to ~100 Hz via electrostatic gating and annealing. To overcome the severe mode mismatch between the CNT plasmon and optical fiber, we introduce a graded plasmonic-photonic mode converter, providing a path to near-unity extraction efficiency. Using a tripod-STIRAP scheme, we demonstrate high-fidelity, magnetically tunable spin-photon entanglement. Our analysis confirms operation deep in the strong-coupling regime, with cooperativities C > 100 and chiral contrast exceeding 20 dB. This wavelength-agnostic architecture is compatible with any solid-state emitter, establishing a scalable blueprint for robust, nonreciprocal quantum nodes in a global quantum internet.
quant-pharXiv:2603.29290•Apr 1, 2026