Microwave-to-optics topological pumping in Fock-state lattices with a nitrogen-vacancy spin

In quantum networks, robust and efficient frequency conversions of photons between microwave (MW) and optical regimes serve as a critical interface bridging superconducting quantum processors and optical communication channels. Recently, a topologically protected paradigm of state transfers, based on the topological nature of quantized light in Fock-state lattices (FSLs), has been demonstrated by a superconducting quantum circuit. However, its extension to quantum networks remains unexplored. Here we develop a topological single-photon MW–optics interface based on FSLs with a single nitrogen-vacancy (NV) center spin embedded in a photonic crystal cavity (PCC). The NV spin mediates the effective strong coupling between the optical PCC mode and a superconducting MW resonator via the adiabatic elimination of an intermediate acoustic mode. This scheme establishes a hybrid MW-NV-optics two-mode Jaynes-Cummings model, yielding a topological FSL. Under the significant constraint of optical mode decay, numerical simulations reveal that the MW-to-optics conversion efficiency can exceed 26% for an input five-photon MW Fock state. This work establishes a topological paradigm for hybrid quantum transduction, offering an efficient solid-state framework for constructing large-scale quantum networks.