Chirality-induced quantum non-reciprocity

Abstract

Chirality, non-reciprocity and quantum correlations are at the centre of a wide range of intriguing effects and applications across natural sciences and emerging quantum technologies. However, the direct link combining these three essential concepts has remained unexplored. Here we establish a chiral non-Hermitian platform with flying atoms and demonstrate chirality-induced non-reciprocal bipartite quantum correlations between two channels: quantum correlation emerges when two spatially separated light beams with the same polarization propagate in opposite directions in the atomic cloud, and it becomes zero when they travel in the same direction. Thus, by just flipping the propagation direction of one of the beams and keeping its polarization the same as the other beam, we can create or annihilate quantum correlations between the two channels. We also show that this non-reciprocal quantum correlation can be extended to multicolour sidebands with Floquet engineering. Our findings may pave the road for realizing one-way quantum effects, such as non-reciprocal squeezing or entanglement, with a variety of chiral devices, for emerging applications in, for example, directional quantum networks or non-reciprocal quantum metrology. Chirality-induced quantum non-reciprocity of cross-channel correlations is demonstrated in a rubidium vapour system by flipping the flow direction of one of the circularly polarized laser beams. It can be extended to multicolour sidebands with Floquet engineering.