Nanophotonic Optical Isolator Controlled by the Internal State of Cold Atoms

• DOI: 10.1103/physrevx.5.041036
• Publication Date: 2015-12-04T12:08:26Z
• Authors: Clément Sayrin; Christian Junge; Rudolf Mitsch; Bernhard Albrecht; Danny O’Shea; Philipp Schneeweiss; Jürgen Volz; Arno Rauschenbeutel
• Keywords: Quantum Physics; Atomic Physics (physics.atom-ph); Physics; QC1-999; FOS: Physical sciences; 01 natural sciences; 7. Clean energy; Physics - Atomic Physics; Photonics; quantum physics; Atomic and Molecular Physics; 0103 physical sciences; Quantum Physics (quant-ph); Physics - Optics; Optics (physics.optics)

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.