Control of spontaneously emitted light lies at the heart of quantum optics. It is essential for diverse applications ranging from miniature lasers and light-emitting diodes, to single-photon sources for quantum information, and to solar energy harvesting. To explore such new quantum optics applications, a suitably tailored dielectric environment is required in which the vacuum fluctuations that control spontaneous emission can be manipulated. Photonic crystals provide such an environment: they strongly modify the vacuum fluctuations, causing the decay of emitted light to be accelerated or slowed down, to reveal unusual statistics, or to be completely inhibited in the ideal case of a photonic bandgap. Here we study spontaneous emission from semiconductor quantum dots embedded in inverse opal photonic crystals. We show that the spectral distribution and time-dependent decay of light emitted from excitons confined in the quantum dots are controlled by the host photonic crystal. Modified emission is observed over large frequency bandwidths of 10%, orders of magnitude larger than reported for resonant optical microcavities. Both inhibited and enhanced decay rates are observed depending on the optical emission frequency, and they are controlled by the crystals’ lattice parameter. Our experimental results provide a basis for all-solid-state dynamic control
of optical quantum systems.

Controlling the dynamics of spontaneous emission from quantum dots by photonic crystals

A proposed network of atomic clocks—using non-local entangled states—could achieve unprecedented stability and accuracy in time-keeping, as well as being secure against internal or external attack.

http://absimage.aps.org/image/DAMOP14/MWS_DAMOP14-2014-000545.pdf

A quantum network of clocks

The application of topology in optics has led to a new paradigm in developing photonic devices with robust properties against disorder Although considerable progress on topological phenomena has been achieved in the classical domain, the realization of strong light-matter coupling in the quantum domain remains unexplored We demonstrate a strong interface between single quantum emitters and topological photonic states Our approach creates robust counterpropagating edge states at the boundary of two distinct topological photonic crystals We demonstrate the chiral emission of a quantum emitter into these modes and establish their robustness against sharp bends This approach may enable the development of quantum optics devices with built-in protection, with potential applications in quantum simulation and sensing

A topological quantum optics interface

With its unique and exclusive linear and nonlinear optical characteristics, epsilon-near-zero (ENZ) photonics has drawn a tremendous amount of attention in the recent decade in the fields of nanophotonics, nonlinear optics, plasmonics, light-matter interactions, material science, applied optical science, etc. The extraordinary optical properties, relatively high tuning flexibility, and CMOS compatibility of ENZ materials make them popular and competitive candidates for nanophotonic devices and on-chip integration in all-optical and electro-optical platforms. With exclusive features and high performance, ENZ photonics can play a big role in optical communications and optical data processing. In this review, we give a focused discussion on recent advances of the theoretical and experimental studies on ENZ photonics, especially in the regime of nonlinear ENZ nanophotonics and its applications. First, we overview the basics of the ENZ concepts, mechanisms, and nonlinear ENZ nanophotonics. Then the new advancements in theoretical and experimental optical physics are reviewed. For nanophotonic applications, the recent decades saw rapid developments in various kinds of different ENZ-based devices and systems, which are discussed and analyzed in detail. Finally, we give our perspectives on where future endeavors can be made.

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Epsilon-near-zero photonics: infinite potentials

Recent research in topological photonics has not only proposed and realized novel topological phenomena such as one‐way broadband propagation and robust transport of light, but also designed and fabricated photonic devices with high‐performance indexes, which are immune to fabrication errors such as defects or disorders. Photonic crystals, which are periodic optical structures with the advantages of good light field confinement and multiple adjusting degrees of freedom, provide a powerful platform to control the flow of light. With the topology defined in the reciprocal space, photonic crystals have been widely used to reveal different topological phases of light and demonstrate topological photonic functionalities. This review presents the physics of topological photonic crystals with different dimensions, models, and topological phases. The design methods of topological photonic crystals are introduced. Furthermore, the applications of topological photonic crystals in passive and active photonics are reviewed. These studies pave the way for applying topological photonic crystals in practical photonic devices.

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Topological Photonic Crystals: Physics, Designs, and Applications

Up to now it remains challenging to couple photons from a circularly polarized emitter into a photonic structure to simultaneously realize strong photon-emitter interaction and unidirectional propagation locked by local helicity of the optical mode at the nanoscale. In this paper we propose a unique approach that combines a photonic crystal and metallic nanoparticle structure to create nanocavities with both strong local-field intensity and high helicity. In this system the rate of circularly polarized photons emitting into the photonic crystal waveguide reaches $148{\ensuremath{\gamma}}_{0}$, which is one order of magnitude larger than that without the nanoparticle, and in the ultranarrow band-edge mode the linewidth of Rabi splitting spectra is about one-tenth of that with the nanoparticle only, both with $\ensuremath{\approx}95%$ of photons propagating unidirectionally along the nanoscale waveguide. We suggest that our paper establishes a nanophotonic interface of chiral quantum electrodynamics for on-chip nonreciprocal quantum light sources, quantum circuits, and scalable quantum networks.

Chiral cavity quantum electrodynamics with coupled nanophotonic structures

We propose the mechanism of edge state-led mode coupling under topological protection; i.e., localized surface plasmons almost do not have any influence on the edge state, while the edge state greatly changes the local field distribution of surface plasmons. Based on this mechanism, in the well-designed topological photonic structure containing a resonant plasmon nanoantenna, an obvious absorption reduction in the spontaneous emission spectra appears due to the near-field deformation around the antenna induced by the edge state. Because a plasmon antenna with ultrasmall mode volume provides large Purcell enhancement and simultaneously the photonic crystal guides almost all scattering light into its edge state, the rate of nonscattering single photons reaches more than 10^{4}γ_{0}. This topological state-led mode coupling mechanism and induced absorption reduction, which are based on topological protection, will have a profound effect on the study of composite topological photonic structures and related micro- and nanoscale cavity quantum electrodynamics. Also, nonscattering large Purcell enhancement will provide practical use for on-chip quantum light sources, such as single-photon sources and nanolasers.

Absorption Reduction of Large Purcell Enhancement Enabled by Topological State-Led Mode Coupling.

Single-photon source in micro- or nanoscale is the basic building block of on-chip quantum information and scalable quantum network. Enhanced spontaneous emission based on cavity quantum electrodynamics (CQED) is one of the key principles of realizing single-photon sources fabricated by micro- or nanophotonic cavities. Here we mainly review the spontaneous emission of single emitters in micro- or nanostructures, such as whispering gallery microcavities, photonic crystals, plasmon nanostructures, metamaterials, and their hybrids. The researches have enriched light-matter interaction as well as made great influence in single-photon source, photonic circuit, and on-chip quantum information.

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Spontaneous emission in micro- or nanophotonic structures

We demonstrate the spectral accumulation of large spontaneous emission (SE) for nanocavities with different sizes in the coupled Ag nanorod and epsilon-near-zero (ENZ) film system. This effect originates from the slowing down of the spectral shift of resonant nanocavities at the wavelength where the permittivity of the substrate vanishes, i.e., the resonance “pinning” near the ENZ frequency. In addition, most far field radiation of the emitter is concentrated in the forward field with small solid angle due to the impedance mismatch between the ENZ film and the free space. This kind of size-relaxed nanocavity for directional SE has potential applications in the bright single photon sources, plasmon-based nanolasers, and on-chip nanodevices.

Accumulation and directionality of large spontaneous emission enabled by epsilon-near-zero film.

Chiral photon-emitter coupling has been extensively explored in its non-reciprocal property, which results from spin-locked photon transmission. It manifests the potential in on-chip non-reciprocal devices, such as optical isolators and photon routing in quantum networks. However, the enhancement of chiral coupling, which has been seldom studied, remains wanting. Here, we numerically propose a gap-plasmon-emitter system demonstrating large Purcell enhancement with effective nanoscale non-reciprocal photon transmission. Owing to the strong field enhancement and high transverse spin momentum (TSM) in gap plasmons, the Purcell factor reaches 104. Simultaneously, the transmission in the nanowire is directional, in which 91% propagates in a single direction. The transmission confined around the nanowire also obtains a ∼700-fold enhancement compared with the vacuum decay rate of the emitter. Furthermore, the circularly polarized emitter couples preferentially to the opposite transmission direction in the two eigenmodes. This phenomenon is attributed to the special TSM profile of the two eigenmodes, that is, the transmission direction is locked to the opposite TSM in the two eigenmodes. Our proposed system offers an efficient way for photon routing in optical circuits and quantum networks and also extends methods for manipulating non-reciprocal devices.

Lingxiao Shan

Papers

Chiral cavity quantum electrodynamics with coupled nanophotonic structures

Absorption Reduction of Large Purcell Enhancement Enabled by Topological State-Led Mode Coupling.

Spontaneous emission in micro- or nanophotonic structures

Accumulation and directionality of large spontaneous emission enabled by epsilon-near-zero film.

Large Purcell enhancement with nanoscale non-reciprocal photon transmission in chiral gap-plasmon-emitter systems.