Engineering synthetic magnetic fields for polarized photons

Abstract Charged particles exhibit nonzero magnetic moments and interact with external magnetic fields, which lead to a rich variety of fundamental spin transport phenomena including the Lorentz force, Landau quantization, Aharonov-Bohm effect and topological Hall effect. Unlike the charged particles, uncharged particles such as photons do not contain spinning-induced magnetic moments and are therefore decoupled from the real magnetic fields. As a result, emulations of the fundamental quantum phenomena by using the uncharged particles are thought to be elusive. Here, we theoretically identify an equivalent spin-1/2 model for polarized photons and synthesize a general magnetization vector for coupling the differently polarized photons in an engineered photonic anisotropic medium. The synthetic magnetic field can be spatially engineered to manipulate the magnetic moments of the pseudo-spin-1/2 photons, leading to observation of the Lorentz force and the resulting analogous Stern–Gerlach phenomena. We experimentally demonstrate these fundamental effects by using different spins including the purely single-polarization spins and mutually two-polarization mixing spins. We report the first demonstration of higher-order Stern–Gerlach effects by using spins, which exhibit nontrivial topological structures. Our findings offer new avenues to polarization-based elements with potential applications such as in photonic polarization selection and conversion, benefiting classical and quantum information processing. This work constitutes a general formulism for synthesizing the magnetic field, allowing emulation of intriguing quantum phenomena such as the topological Hall effect by using the polarized photons.