Topological lasers are immune to imperfections and disorder. They have been recently demonstrated based on many kinds of robust edge states, which are mostly at the microscale. The realization of 2D on-chip topological nanolasers with a small footprint, a low threshold and high energy efficiency has yet to be explored. Here, we report the first experimental demonstration of a topological nanolaser with high performance in a 2D photonic crystal slab. A topological nanocavity is formed utilizing the Wannier-type 0D corner state. Lasing behaviour with a low threshold of approximately 1 µW and a high spontaneous emission coupling factor of 0.25 is observed with quantum dots as the active material. Such performance is much better than that of topological edge lasers and comparable to that of conventional photonic crystal nanolasers. Our experimental demonstration of a low-threshold topological nanolaser will be of great significance to the development of topological nanophotonic circuitry for the manipulation of photons in classical and quantum regimes.
Recent theoretical studies have extended the Berry phase framework to account for higher electric multipole moments, quadrupole and octupole topological phases have been proposed.Although the two-dimensional quantized quadrupole insulators have been demonstrated experimentally, octupole topological phases have not previously been observed experimentally.Here we report on the experimental realization of classical analog of octupole topological insulator in the electric circuit system. Three-dimensional topolectrical circuits for realizing such topological phases are constructed experimentally. We observe octupole topological states protected by the topology of the bulk, which are localized at the corners. Our results provide conclusive evidence of a form of robustness against disorder and deformation, which is characteristic of octupole topological insulators. Our study opens a new route toward higherorder topological phenomena in three-dimensions and paves the way for employing topolectrical circuitry to study complex topological phenomena.
Recently, a new family of symmetry-protected higher-order topological insulators has been proposed, and was shown to host lower-dimensional boundary states. However, with the existence of the strong disorder in the bulk, the crystal symmetry is broken, and the associated corner states are disappeared. It is well known that the emergence of robust edge states and quantized transport can be induced by adding sufficient disorders into a topologically trivial insulator, that is the so-called topological Anderson insulator. The question is whether disorders can also cause the higher-order topological phase. This is not known so far, because the interaction between disorders and the higher-order topological phases is completely different from that with the first-order topological system.Here, we demonstrate theoretically that the disorder-induced higher-order topological corner state can appear in a modified Haldane model. In experiments, we construct the classical analog of such higher-order topological Anderson insulators using electric circuits, and observe the disorder-induced corner state through the voltage measurement.Our work defies the conventional view that the disorder is detrimental to the higher-order topological phase, and offers a feasible platform to investigate the interaction between disorders and the higher-order topological phases.
Topological photonics provides a new paradigm in studying cavity quantum electrodynamics with robustness to disorder. In this work, the coupling between single quantum dots and the second‐order topological corner state are demonstrated. Based on the second‐order topological corner state, a topological photonic crystal cavity is designed and fabricated into GaAs slabs with quantum dots embedded. The coexistence of corner state and edge state with high quality factor close to 2000 is observed. The enhancement of photoluminescence intensity and emission rate are both observed when the quantum dot is on resonance with the corner state. This result enables the application of topology into cavity quantum electrodynamics, offering an approach to topological devices for quantum information processing.
ABSTRACT:We present a rigorous finite element method to calculate circular dichroism (CD) in various systems consisting of nanostructures and oriented chiral molecules with electric quadrupole transitions. The interaction between oriented molecule materials, which are regarded as anisotropic chiral media, and metallic nanostructures has been investigated. Our results show that the plasmon-induced CD is sensitive to the orientations of the molecules. In many cases, the contribution of molecular electric quadrupole transitions to the total CD signal can play a key role. More interesting, we have demonstrated that both the quadrupole-and dipole-based CD signals can be improved greatly by matching the phases for the electromagnetic fields and their gradients at different regions around the nanostructures, which are occupied by the oriented chiral molecules. Different regions might produce CD of opposite sign. When integrating over regions with only one side of the proposed nanostructure, we find that the CD-peak may be nearly hundreds-fold over the case of integrating both sides. We believe that these findings would be helpful for realizing ultrasensitive probing of chiral information for oriented molecules by plasmon-based nanotechnology. 2 I.INTRODUCTIONChirality, which refers to structures lacking any mirror symmetry planes, is a very intriguing property of molecules. Many biologically active molecules are chiral, which plays a pivotal role in biochemistry and the evolution of life itself.1-2 Detecting and characterizing chiral enantiomers of these biomolecules are of considerable importance for biomedical diagnostics and pathogen analyses. 3 A common technique for chirality discrimination is CD spectroscopy describing the difference in molecular absorption of left-and right-handed circularly polarized photons. [4][5] In general, the molecular CD signal is typically weak, thus, chiral analyses by such a spectroscopic technique have usually been restricted to analysis at a relatively high concentration. 1-5Recent investigations have shown that superchiral fields allow measuring the chiroptical properties of small amounts of molecules with high sensitivity. 6-7 A weak molecular CD signal in the ultraviolet spectral region can be both enhanced and transferred to the visible-near-infrared region when chiral molecules are adsorbed at the surfaces of metallic nanoparticles or in the nanogaps (i.e., hot spots) of particle clusters. However, many related discussions assume that the molecules are randomly oriented, 6, 21-24 and the results have been obtained by averaging over the solid angles of the molecular directions. In fact, this rotational degree of freedom for molecules is absent in many cases, i.e. chiral molecules adopt geometries in which they have an axis with a well-defined orientation with respect to the surface of the nanostructures. 9,[26][27][28][29] This leads to several orientation-selective signals for appropriately sculpted fields. Although there are also some theoretical researches concentrating o...
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