Twisted Cavity Is a One-Way Light Path

At the microscopic scale, most systems would behave the same if we ran the cosmic clock in reverse. But this time-reversal symmetry is broken in certain cases, such as for electrons inside materials exhibiting quantum Hall effects. A new optical device breaks time-reversal symmetry for photons using a twisted optical cavity containing spin-polarized atoms. Unlike previous time-asymmetric optical devices, this design is compatible with quantum simulation experiments, in which trapped photons are made to behave like massive, interacting particles.