To enable precise control of photons, a Stanford-led team created a pseudo-magnetic force, essentially “tricking” photons — which are intrinsically nonmagnetic — into behaving like charged electrons. The photons were sent through carefully designed mazes in a way that caused them to behave as if they were being acted upon by what the scientists call a “synthetic” magnetic field. “We designed structures that created magnetic forces capable of pushing photons in predictable and useful ways,” professor Shanhui Fan said. The concept of synthetic dimensions has generated interest in many branches of science. Previous experiments have augmented the real-space dimensionality by one additional physical synthetic dimension. In the Stanford study, the researchers provided a single ring resonator with two independent physical synthetic dimensions. The temporally modulated ring resonator had spatial coupling between the clockwise and counterclockwise modes, which created a synthetic Hall ladder along the frequency and pseudospin degrees of freedom for the photons propagating in the ring. The researchers were able to observe a variety of physics, including effective spin-orbit coupling, magnetic fields, spin-momentum locking, a Meissner-to-vortex phase transition, and signatures of topological chiral one-way edge currents, completely within the synthetic dimensions. To develop technologies like quantum computers, scientists will need to find ways to control photons as precisely as they can now control electrons. By leveraging the concept of multiple simultaneous synthetic dimensions, the researchers demonstrated that higher-dimensional physics could be studied in simple systems. In the future, the Stanford team’s approach could lead to the creation of light-based chips that would deliver greater computational power than electronic chips. “What we’ve done is so novel that the possibilities are only just beginning to materialize,” researcher Avik Dutt said. To bring photons into the proximities required to create these magnetic effects, the Stanford researchers used lasers, fiber optic cables, and other off-the-shelf scientific equipment. Building these tabletop structures enabled the scientists to deduce the design principles behind the effects they discovered. In the future, the researchers want to create nanoscale structures that embody these principles to build a chip. In the meantime, Fan said, “we’ve found a relatively simple new mechanism to control light, and that’s exciting.” The research was published in Science (https://doi.org/10.1126/science.aaz3071).