Observation of an Effective Magnetic field for Light

Photons are neutral particles that do not interact directly with a magnetic field. However, recent theoretical work has shown that an effective magnetic field for photons can exist if the phase of light would change with its propagating direction. This direction-dependent phase indicates the presence of an effective magnetic field as shown for electrons experimentally in the Aharonov-Bohm experiment. Here we replicate this experiment using photons. In order to create this effective magnetic field, we construct an on-chip silicon-based Ramsey-type interferometer. This interferometer has been traditionally used to probe the phase of atomic states, and here we apply it to probe the phase of photonic states. We experimentally observe a phase change, i.e. an effective magnetic field flux from 0 to 2pi. In an Aharonov-Bohm configuration for electrons, considering the device geometry, this flux corresponds to an effective magnetic field of 0.2 Gauss.