Topological photonics is a rapidly emerging field of research in which geometrical and topological ideas are exploited to design and control the behavior of light. Drawing inspiration from the discovery of the quantum Hall effects and topological insulators in condensed matter, recent advances have shown how to engineer analogous effects also for photons, leading to remarkable phenomena such as the robust unidirectional propagation of light, which hold great promise for applications. Thanks to the flexibility and diversity of photonics systems, this field is also opening up new opportunities to realize exotic topological models and to probe and exploit topological effects in new ways. This article reviews experimental and theoretical developments in topological photonics across a wide range of experimental platforms, including photonic crystals, waveguides, metamaterials, cavities, optomechanics, silicon photonics, and circuit QED. A discussion of how changing the dimensionality and symmetries of photonics systems has allowed for the realization of different topological phases is offered, and progress in understanding the interplay of topology with non-Hermitian effects, such as dissipation, is reviewed. As an exciting perspective, topological photonics can be combined with optical nonlinearities, leading toward new collective phenomena and novel strongly correlated states of light, such as an analog of the fractional quantum Hall effect.

Topological Photonics

This Review article provides an overview of the fundamental origins and important applications of the main spin–orbit interaction phenomena in modern optics that play a crucial role at subwavelength scales. Light carries both spin and orbital angular momentum. These dynamical properties are determined by the polarization and spatial degrees of freedom of light. Nano-optics, photonics and plasmonics tend to explore subwavelength scales and additional degrees of freedom of structured — that is, spatially inhomogeneous — optical fields. In such fields, spin and orbital properties become strongly coupled with each other. In this Review we cover the fundamental origins and important applications of the main spin–orbit interaction phenomena in optics. These include: spin-Hall effects in inhomogeneous media and at optical interfaces, spin-dependent effects in nonparaxial (focused or scattered) fields, spin-controlled shaping of light using anisotropic structured interfaces (metasurfaces) and robust spin-directional coupling via evanescent near fields. We show that spin–orbit interactions are inherent in all basic optical processes, and that they play a crucial role in modern optics.

Spin-orbit interactions of light

Spinorbit coupling in electrons leads to many fascinating phenomena and important applications, from topological insulators to spintronics. Researchers have recently been exploring whether effects analogous to spinorbit coupling can arise in photons and, if so, what sort of perspectives this provides. Optical spinorbit coupling can lead to direction-dependent emissions and so may allow quantum optics to be chiral. This Review looks at experiments in the realm of chiral quantum optics and discusses how these demonstrations could add a new dimension of control to quantum networks and quantum many-body physics.

Chiral quantum optics

第12次 아시아ㆍ太平洋 矯政局長會議 參加記

Microwave photonics with superconducting quantum circuits

Nanoscale confinement in an optical fibre induces coupling between a photon’s spin and orbital angular momentum. Here, the authors use this effect to control the direction of photons spontaneously emitted from trapped caesium atoms into a nanofibre.

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Quantum state-controlled directional spontaneous emission of photons into a nanophotonic waveguide

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.

Optical diode based on the chirality of guided photons

Tapered optical fibers with a nanofiber waist are versatile light–matter interfaces. Of particular interest are laser-cooled atoms trapped in the evanescent field surrounding the optical nanofiber: they exhibit both long ground-state coherence times and efficient coupling to fiber-guided fields. Here, we demonstrate electromagnetically induced transparency, slow light, and the storage of fiber-guided optical pulses in an ensemble of cold atoms trapped in a nanofiber-based optical lattice. We measure group velocities of 50 m/s. Moreover, we store optical pulses at the single-photon level and retrieve them on demand in the fiber after 2 μs with an overall efficiency of (3.0±0.4)%. Our results show that nanofiber-based interfaces for cold atoms have great potential for the realization of building blocks for future optical quantum information networks.

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Storage of fiber-guided light in a nanofiber-trapped ensemble of cold atoms

A technique of trapping and cooling atoms is experimentally demonstrated with an optical microtrap created in the near field of optical nanofibers, which makes an important step forward in the development of nanostructure-based interfaces for interrogating and manipulating cold atoms.

Fictitious magnetic-field gradients in optical microtraps as an experimental tool for interrogating and manipulating cold atoms

A strongly confined light field necessarily exhibits a local polarization that varies on a subwavelength scale. We demonstrate that a single optical mode of this kind can be used to selectively and simultaneously manipulate atomic ensembles that are less than a micron away from each other and equally coupled to the light field. The technique is implemented with an optical nanofiber that provides an evanescent field interface between a strongly guided optical mode and two diametric linear arrays of cesium atoms. Using this single optical mode, the two atomic ensembles can simultaneously be optically pumped to opposite Zeeman states. Moreover, the state-dependent light shifts can be made locally distinct, thereby enabling an independent coherent manipulation of the two ensembles. Our results open a route toward advanced manipulation of atomic samples in nanoscale quantum optics systems.

B. Albrecht

Papers

Quantum state-controlled directional spontaneous emission of photons into a nanophotonic waveguide

Optical diode based on the chirality of guided photons

Storage of fiber-guided light in a nanofiber-trapped ensemble of cold atoms

Fictitious magnetic-field gradients in optical microtraps as an experimental tool for interrogating and manipulating cold atoms

Exploiting the local polarization of strongly confined light for sub-micrometer-resolution internal state preparation and manipulation of cold atoms