  Quantum states induced by single-atomic impurities are at the frontier of
physics and material science. While such states have been reported in
high-temperature superconductors and dilute magnetic semiconductors, they are
unexplored in topological magnets which can feature spin-orbit tunability. Here
we use spin-polarized scanning tunneling microscopy/spectroscopy (STM/S) to
study the engineered quantum impurity in a topological magnet Co3Sn2S2. We find
that each substituted In impurity introduces a striking localized bound state.
Our systematic magnetization-polarized probe reveals that this bound state is
spin-down polarized, in lock with a negative orbital magnetization. Moreover,
the magnetic bound states of neighboring impurities interact to form quantized
orbitals, exhibiting an intriguing spin-orbit splitting, analogous to the
splitting of the topological fermion line. Our work collectively demonstrates
the strong spin-orbit effect of the single-atomic impurity at the quantum
level, suggesting that a nonmagnetic impurity can introduce spin-orbit coupled
magnetic resonance in topological magnets.
