Speaker
Description
The ability to engineer chiral spin-photon interactions is essential for exploring quantum networks and non-reciprocal quantum optics. Here, we demonstrate chiral coupling of a negatively charged quantum dot spin, i.e., a four-level system, embedded in a standard W1 photonic-crystal waveguide. Despite the absence of global chirality, we observe spin-dependent directional emission of 0.77$\pm$0.02 and extract a chiral phase of 0.28$\pm$0.01$\pi$ in the Faraday magnetic fields. %By transitioning to the Voigt geometry, we characterize the intrinsic cyclicity of the inner and outer $\Lambda$-system transitions to be $\sim6$.
By tuning the magnetic-field orientation, we achieve dynamic control over the polarization of individual optical transitions, enabling perfect directional emission (0.99$\pm$0.01) with imperfect polarization. In a two-sided waveguide, this control allows a selected transition to decay exclusively into a single propagation direction. We further observe two tunable chiral cyclicities between two $\Lambda$-systems, with upper bound values reaching up to 134 (72.4–323). Finally, we show a proof-of-concept that this local chirality enables remote optical control of electron spin rotation via an optical Raman process mediated by waveguide transmission. This approach is expected to reduce the required driving power and suppress laser-induced spin decoherence. Building on the simultaneous realization of high cyclicity and directionality, we propose a single-click protocol with high loss tolerance for generating remote spin--spin entanglement. Our results establish the magnetic field as a powerful degree of freedom for engineering chirality in standard nanophotonic interfaces.