A synthetic Hall effect creates strong photonic nonreciprocity

The ordinary Hall effect is a historically well-known physical phenomenon where a transverse electric field is produced when a magnetic field is applied perpendicular to a current. The inverse of this effect, where orthogonal electric and magnetic fields induce an electric current in the E x B direction, is a less well-known but an equally valid application of the same principle. Here, we experimentally realize this combination of effective electric and magnetic fields in a photonic resonator chain through use of synthetic dimensions. We then demonstrate the photonic equivalent of the Hall effect, where the combination of fields creates a “photon current” such that transmission of photons is unidirectionally suppressed. We show that this synthetic Hall effect can induce strongly nonreciprocal transmission, with greater than 58 dB of contrast, when both synthetic fields are tuned to maximize their respective symmetry breaking. This mechanism is general can be applied to break reciprocity in a wide variety of domains, including optical, microwave, and mechanical systems.