title: Deterministic photon-emitter coupling in chiral photonic circuits.
abstract: Engineering photon emission and scattering is central to modern photonics applications ranging from light harvesting to quantum-information processing. To this end, nanophotonic waveguides are well suited as they confine photons to a one-dimensional geometry and thereby increase the light-matter interaction. In a regular waveguide, a quantum emitter interacts equally with photons in either of the two propagation directions. This symmetry is violated in nanophotonic structures in which non-transversal local electric-field components imply that photon emission and scattering may become directional. Here we show that the helicity of the optical transition of a quantum emitter determines the direction of single-photon emission in a specially engineered photonic-crystal waveguide. We observe single-photon emission into the waveguide with a directionality that exceeds 90% under conditions in which practically all the emitted photons are coupled to the waveguide. The chiral light-matter interaction enables deterministic and highly directional photon emission for experimentally achievable on-chip non-reciprocal photonic elements. These may serve as key building blocks for single-photon optical diodes, transistors and deterministic quantum gates. Furthermore, chiral photonic circuits allow the dissipative preparation of entangled states of multiple emitters for experimentally achievable parameters, may lead to novel topological photon states and could be applied for directional steering of light.
authors.affiliation: Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, Copenhagen DK-2100, Denmark.
authors.forename: Immo
authors.identifier: http://orcid.org/0000-0001-7528-8633
authors.initials: I
authors.lastname: Söllner
authors.affiliation: Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, Copenhagen DK-2100, Denmark.
authors.forename: Sahand
authors.initials: S
authors.lastname: Mahmoodian
authors.affiliation: Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, Copenhagen DK-2100, Denmark.
authors.forename: Sofie Lindskov
authors.initials: SL
authors.lastname: Hansen
authors.affiliation: Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, Copenhagen DK-2100, Denmark.
authors.forename: Leonardo
authors.initials: L
authors.lastname: Midolo
authors.affiliation: Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, Copenhagen DK-2100, Denmark.
authors.forename: Alisa
authors.initials: A
authors.lastname: Javadi
authors.affiliation: Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, Copenhagen DK-2100, Denmark.
authors.forename: Gabija
authors.initials: G
authors.lastname: Kiršanskė
authors.affiliation: Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, Copenhagen DK-2100, Denmark.
authors.forename: Tommaso
authors.identifier: http://orcid.org/0000-0003-4062-8102
authors.initials: T
authors.lastname: Pregnolato
authors.affiliation: Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, Copenhagen DK-2100, Denmark.
authors.forename: Haitham
authors.initials: H
authors.lastname: El-Ella
authors.affiliation: Center for Opto-Electronic Convergence Systems, Korea Institute of Science and Technology, Seoul 136-791, Korea.
authors.forename: Eun Hye
authors.initials: EH
authors.lastname: Lee
authors.affiliation: Center for Opto-Electronic Convergence Systems, Korea Institute of Science and Technology, Seoul 136-791, Korea.
authors.forename: Jin Dong
authors.initials: JD
authors.lastname: Song
authors.affiliation: Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, Copenhagen DK-2100, Denmark.
authors.forename: Søren
authors.identifier: http://orcid.org/0000-0002-0991-041X
authors.initials: S
authors.lastname: Stobbe
authors.affiliation: Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, Copenhagen DK-2100, Denmark.
authors.forename: Peter
authors.initials: P
authors.lastname: Lodahl