Optical diode based on the chirality of guided photons

TL;DR

This paper demonstrates a novel optical diode that uses the chirality of confined photons in nanofibres to achieve nonreciprocal light transmission at the single-photon level, with potential applications in quantum photonics.

Contribution

It introduces the first nonreciprocal nanophotonic device exploiting photon chirality, using atomic states to control optical isolation and transmission.

Findings

Achieved high optical isolation with controlled forward transmission.

Demonstrated nonreciprocal transmission at the single-photon level.

Controlled optical diode operation via atomic internal states.

Abstract

Photons are nonchiral particles: their handedness can be both left and right. However, when light is transversely confined, it can locally exhibit a transverse spin whose orientation is fixed by the propagation direction of the photons. Confined photons thus have chiral character. Here, we employ this to demonstrate nonreciprocal transmission of light at the single-photon level through a silica nanofibre in two experimental schemes. We either use an ensemble of spin-polarised atoms that is weakly coupled to the nanofibre-guided mode or a single spin-polarised atom strongly coupled to the nanofibre via a whispering-gallery-mode resonator. We simultaneously achieve high optical isolation and high forward transmission. Both are controlled by the internal atomic state. The resulting optical diode is the first example of a new class of nonreciprocal nanophotonic devices which exploit the chirality of confined photons and which are, in principle, suitable for quantum information processing and future quantum optical networks.