Optical isolation promises very important applications in protecting lasers from damage by backscatter of light, integrated photonics, and quantum information processing. Here, we present four schemes for optical isolators and circulators, based on the chiral WGM cavity/waveguide QED. (1) By coupling a single quantum emitter asymmetrically to a chiral optical cavity or a chiral waveguide, we propose methods for the optical isolator and circulator at the single-photon level. The Vienna Center for Quantum Science and Technology experimentally demonstrated all our concepts. (2) We propose an on-chip single-photon isolator. It improves the nonreciprocal band for optical isolation by three orders in comparison with the reported schemes based chiral atom-light interaction. (3) By inserting an ensemble of warm Rb atoms in a three-mirror ring resonator, we achieved a collectively strong coupling between atoms and the resonator mode. Making use of the microscopic Doppler shift of atomic resonance frequencies due to the thermal motion of atoms, we experimentally created a chiral susceptibility of atoms for the probe light. Furthermore, we achieved the optical nonreciprocal propagation and isolation at room temperature. (4) We also propose a method to create a chiral cross-Kerr optical nonlinearity in an ensemble of Rb atoms, implanted in a 1D waveguide. This chiral XKerr nonlinearity overcomes the dynamical reciprocity problem in nonlinear optics and allow one to realize optical isolators and circulators at room temperature. Our achievements may promise many applications in quantum information processing.

Dr. Keyu Xia is currently a full professor working at the College of Engineering and Applied Sciences in Nanjing University. He received his Doctoral degree of “Optics” in 2007 from Shanghai Institute of Optics and Fine Mechanics, CAS. He has been working in Max-Planck Institute for Nuclear Physics in Germany, Texas A&M University in USA, and Macquarie University in Australia. In 2017, he joined Nanjing University as a professor. Dr. Xia concentrates on the field of quantum optics and quantum information superconducting quantum circuits, quantum network, quantum metrology and quantum nonlinear optics. He has 40 peer-reviewed publications in the top-level journals including Science, Nature Photonics, PRL, PRX and so on. His works have been reported by Science Magazine, Nature Photonics and media Phys. Org. The theoretical proposals for single-photon isolation have been realized by Prof. Arno Rauschenbeutel’s experimental group in Vienna Center of Quantum Science and Technology. His recent work of “Thermal-motion-induced quantum optical system”, published in Nature Photonics, is selected as “Top-10 progresses of Optics in China in 2018-Fundamental Research”.