title: Quantum optical circulator controlled by a single chirally coupled atom.
abstract: Integrated nonreciprocal optical components, which have an inherent asymmetry between their forward and backward propagation direction, are key for routing signals in photonic circuits. Here, we demonstrate a fiber-integrated quantum optical circulator operated by a single atom. Its nonreciprocal behavior arises from the chiral interaction between the atom and the transversally confined light. We demonstrate that the internal quantum state of the atom controls the operation direction of the circulator and that it features a strongly nonlinear response at the single-photon level. This enables, for example, photon number-dependent routing and novel quantum simulation protocols. Furthermore, such a circulator can in principle be prepared in a coherent superposition of its operational states and may become a key element for quantum information processing in scalable integrated optical circuits.
authors.affiliation: Vienna Center for Quantum Science and Technology, Atominstitut, Technischen Universität Wien Stadionallee 2, 1020 Vienna, Austria.
authors.forename: Michael
authors.initials: M
authors.lastname: Scheucher
authors.affiliation: Vienna Center for Quantum Science and Technology, Atominstitut, Technischen Universität Wien Stadionallee 2, 1020 Vienna, Austria.
authors.forename: Adèle
authors.initials: A
authors.lastname: Hilico
authors.affiliation: Vienna Center for Quantum Science and Technology, Atominstitut, Technischen Universität Wien Stadionallee 2, 1020 Vienna, Austria.
authors.forename: Elisa
authors.initials: E
authors.lastname: Will
authors.affiliation: Vienna Center for Quantum Science and Technology, Atominstitut, Technischen Universität Wien Stadionallee 2, 1020 Vienna, Austria. jvolz@ati.ac.at arno.rauschenbeutel@ati.ac.at.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Volz
authors.affiliation: Vienna Center for Quantum Science and Technology, Atominstitut, Technischen Universität Wien Stadionallee 2, 1020 Vienna, Austria. jvolz@ati.ac.at arno.rauschenbeutel@ati.ac.at.
authors.forename: Arno
authors.initials: A
authors.lastname: Rauschenbeutel