Left to its own ways, light will follow the same path through an optical system whether the system is being used as a camera lens or as a projector. This is called time-reversal symmetry, or reciprocity. As many new applications and methods would be enabled by access to a non-reciprocal optical system, it is unfortunate that they have been so difficult to come by. But now researchers at Stanford University have discovered how to make such non-reciprocal systems by generating an effective magnetic field for photons.
Read the full article: Stanford researchers control light using synthetic magnetism