Noiseless photonic non-reciprocity via optically-induced magnetization.

The realization of optical non-reciprocity is crucial for many applications, and also of fundamental importance for manipulating and protecting the photons with desired time-reversal symmetry. Recently, various new mechanisms of magnetic-free non-reciprocity have been proposed and implemented, avoiding the limitation of the strong magnetic field imposed by the Faraday effect. However, due to the difficulties in separating the signal photons from the drive laser and the noise photons induced by the drive laser, these devices exhibit limited isolation performances and their quantum noise properties are rarely studied. Here, we demonstrate an approach of magnetic-free non-reciprocity by optically-induced magnetization in an atom ensemble. Excellent isolation (highest isolation ratio is $$51.{5}_{-2.5}^{+6.5}\ {\rm{dB}}$$ ) is observed over a power dynamic range of 7 orders of magnitude, with the noiseless property verified by quantum statistics measurements. The approach is applicable to other atoms and atom-like emitters, paving the way for future studies of integrated photonic non-reciprocal devices. Optical nonreciprocity through magneto-optical effects requires bulky apparatuses and strong magnetic fields, while magnetic-free approaches are difficult to implement. Here, the authors use optically-induced magnetisation in an atomic ensemble to get 50 dB of isolation over a large power dynamic range.