Publisher's Note: Coherence-Driven Topological Transition in Quantum Metamaterials [Phys. Rev. Lett. 116, 165502 (2016)].

This corrects the article DOI: 10.1103/PhysRevLett.116.165502.

Coherence-Driven Topological Transition in Quantum Metamaterials.

We introduce and theoretically demonstrate a quantum metamaterial made of dense ultracold neutral atoms loaded into an inherently defect-free artificial crystal of light, immune to well-known critical challenges inevitable in conventional solid-state platforms. We demonstrate an all-optical control, on ultrafast time scales, over the photonic topological transition of the isofrequency contour from an open to closed topology at the same frequency. This atomic lattice quantum metamaterial enables a dynamic manipulation of the decay rate branching ratio of a probe quantum emitter by more than an order of magnitude. Our proposal may lead to practically lossless, tunable, and topologically reconfigurable quantum metamaterials, for single or few-photon-level applications as varied as quantum sensing, quantum information processing, and quantum simulations using metamaterials.

Metasurface-Enabled Remote Quantum Interference.

An anisotropic quantum vacuum (AQV) opens novel pathways for controlling light-matter interaction in quantum optics, condensed matter physics, etc. Here, we theoretically demonstrate a strong AQV over macroscopic distances enabled by a judiciously designed array of subwavelength-scale nanoantennas-a metasurface. We harness the phase-control ability and the polarization-dependent response of the metasurface to achieve strong anisotropy in the decay rate of a quantum emitter located over distances of hundreds of wavelengths. Such an AQV induces quantum interference among radiative decay channels in an atom with orthogonal transitions. Quantum vacuum engineering with metasurfaces holds promise for exploring new paradigms of long-range light-matter interaction for atom optics, solid-state quantum optics, quantum information processing, etc.

Fano-resonant asymmetric metamaterials for ultrasensitive spectroscopy and identification of molecular monolayers.

Engineered optical metamaterials present a unique platform for biosensing applications owing to their ability to confine light to nanoscale regions and to their spectral selectivity. Infrared plasmonic metamaterials are especially attractive because their resonant response can be accurately tuned to that of the vibrational modes of the target biomolecules. Here we introduce an infrared plasmonic surface based on a Fano-resonant asymmetric metamaterial exhibiting sharp resonances caused by the interference between subradiant and superradiant plasmonic resonances. Owing to the metamaterial's asymmetry, the frequency of the subradiant resonance can be precisely determined and matched to the molecule's vibrational fingerprints. A multipixel array of Fano-resonant asymmetric metamaterials is used as a platform for multispectral biosensing of nanometre-scale monolayers of recognition proteins and their surface orientation, as well as for detecting chemical binding of target antibodies to recognition proteins.

Design of metamaterial surfaces with broadband absorbance.

A simple design paradigm for making broadband ultrathin plasmonic absorbers is introduced. The absorber's unit cell is composed of subunits of various sizes, resulting in nearly 100% absorbance at multiple adjacent frequencies and high absorbance over a broad frequency range. A simple theoretical model for designing broadband absorbers is presented. It uses a single-resonance model to describe the optical response of each subunit and employs the series circuit model to predict the overall response. Validity of the circuit model relies on short propagation lengths of the surface plasmons.

Real-space mapping of Fano interference in plasmonic metamolecules.

An unprecedented control of the spectral response of plasmonic nanoantennas has recently been achieved by designing structures that exhibit Fano resonances. This new insight is paving the way for a variety of applications, such as biochemical sensing and surface-enhanced Raman spectroscopy. Here we use scattering-type near-field optical microscopy to map the spatial field distribution of Fano modes in infrared plasmonic systems. We observe in real space the interference of narrow (dark) and broad (bright) plasmonic resonances, yielding intensity and phase toggling between different portions of the plasmonic metamolecules when either their geometric sizes or the illumination wavelength is varied.

DNA-enabled self-assembly of plasmonic nanoclusters.

DNA nanotechnology provides a versatile foundation for the chemical assembly of nanostructures. Plasmonic nanoparticle assemblies are of particular interest because they can be tailored to exhibit a broad range of electromagnetic phenomena. In this Letter, we report the assembly of DNA-functionalized nanoparticles into heteropentamer clusters, which consist of a smaller gold sphere surrounded by a ring of four larger spheres. Magnetic and Fano-like resonances are observed in individual clusters. The DNA plays a dual role: it selectively assembles the clusters in solution and functions as an insulating spacer between the conductive nanoparticles. These particle assemblies can be generalized to a new class of DNA-enabled plasmonic heterostructures that comprise various active and passive materials and other forms of DNA scaffolding.

Broadband slow light metamaterial based on a double-continuum Fano resonance.

We propose a concept of a low-symmetry three-dimensional metamaterial exhibiting a double-continuum Fano (DCF) optical resonance. Such metamaterial is described as a birefringent medium supporting a discrete dark electromagnetic state weakly coupled to the continua of two nondegenerate bright bands of orthogonal polarizations. It is demonstrated that light propagation through such DCF metamaterial can be slowed down over a broad frequency range when the medium parameters (e.g., frequency of the dark mode) are adiabatically changed along the optical path. Using a specific metamaterial implementation, we demonstrate that the DCF approach to slow light is superior to that of the electromagnetically induced transparency because it enables spectrally uniform group velocity and transmission coefficient.

Fano-like interference in self-assembled plasmonic quadrumer clusters.

Assemblies of strongly interacting metallic nanoparticles are the basis for plasmonic nanostructure engineering. We demonstrate that clusters of four identical spherical particles self-assembled into a close-packed asymmetric quadrumer support strong Fano-like interference. This feature is highly sensitive to the polarization of the incident electric field due to orientation-dependent coupling between particles in the cluster. This structure demonstrates how careful design of self-assembled colloidal systems can lead to the creation of new plasmonic modes and the enabling of interference effects in plasmonic systems.

Radiative engineering of plasmon lifetimes in embedded nanoantenna arrays.

It is generally accepted that the lifetimes of the localized plasmonic excitations are inherently controlled by the type of the metals and the shape of the nanoparticles. However, extended plasmonic lifetimes and enhanced near-fields in nanoparticle arrays can be achieved as a result of collective excitation of plasmons. In this article, we demonstrate significantly longer plasmon lifetimes and stronger near-field enhancements by embedding the nanoantenna arrays into the substrate. Our approach offers a more homogeneous dielectric background allowing stronger diffractive couplings among plasmonic particles leading to strong suppression of the radiative damping. We observe near-field enhancements well beyond than those achievable with isolated nanoparticles. Enhanced fields obtained in these structures could be attractive for biosensing and non-linear photonics applications.

Interferometric characterization of a sub-wavelength near-infrared negative index metamaterial.

Negative phase advance through a single layer of near-IR negative index metamaterial (NIM) is identified through interferometric measurements. The NIM unit cell, sub-wavelength in both the lateral and light propagation directions, is comprised of a pair of Au strips separated by two dielectric and one Au film. Numerical simulations show that the negative phase advance through the single-layer sample is consistent with the negative index exhibited by a bulk material comprised of multiple layers of the same structure. We also numerically demonstrate that the negative index band persists in the lossless limit.

Metal biosorption capability of Cupriavidus taiwanensis and its effects on heavy metal removal by nodulated Mimosa pudica.

A novel metal biosorption system consisting of the symbiotic combination of an indigenous metal-resistant rhizobial strain, Cupriavidus taiwanensis TJ208, and its host plant Mimosa pudica has been developed for the removal of heavy-metal pollutants. Free-living C. taiwanensis TJ208 cells were able to adsorb 50.1, 19.0, and 19.6 mg/g of Pb, Cu, and Cd, respectively. After nodulation via inoculation with strain TJ208, the metal uptake ability of M. pudica markedly increased, as the nodulated M. pudica displayed a high metal uptake capacity (qmax) of 485, 25, and 43 mg/g, respectively, which is 86, 12, and 70% higher than that of nodule-free plants. Moreover, with TJ208 nodules, the M. pudica plant also displayed a 71, 81, and 33% enhancement in metal adsorption efficiency (eta) for Pb, Cu, and Cd, respectively. The nodulation appeared to give the greatest enhancing effect on the uptake of Pb, which is consistent with the preference of metal adsorption ability of TJ208. This seems to indicate the crucial role that the rhizobial strain may play in stimulating metal uptake of the nodulated plant. Furthermore, the results show that metal accumulation in the nodulated plant mainly occurred in the roots, accounting for 65-95% of total metal uptake. In contrast, the nodules and the shoots only contributed to 3-12 and 2-23% of total metal uptake, respectively. Nevertheless, the specific adsorption capacity of nodules is comparable to that of the roots. Hence, this work demonstrates the feasibility and effectiveness of using the nodulated plants to promote phyto-removal of heavy metals from the polluted environment as well as to restrict the metal contaminants in the unharmful region of the plant.

An assessment of the toxicity of metals to Pseudomonas aeruginosa PU21 (Rip64).

The toxicity of Co(II), Mn(II), Cd(II), and Zn(II) for Pseudomonas aeruginosa PU21, a Hg(II)-hyperresistant strain containing the mercury resistance mer operon, was determined. The metal tolerance of PU21 was strongly influenced by environmental conditions (e.g., existing metal, medium composition). Dose-response analysis on chronic and acute toxicity (e.g., EC(20), median effective dose EC(50), and slope factor B) of divalent cobalt, manganese, cadmium, and zinc cations in LB medium amended with citric acid phosphate buffered saline (CAPBS) suggested a toxicity series of Co > Mn approximately Zn > Cd for EC(50). In contrast, excluding the likely precipitate of Zn(II), the toxicity ranking in phosphate-buffered saline (PBS)-amended LB medium was Co > Cd > Mn. The metal toxicity in PBS, irrespective of metals, was greater than that in CAPBS. This might be attributed to the presence of citric acid in CAPBS as a chelating ligand donating electrons to hold free metals (e.g., Cd(2+), Zn(2+) tetrahedral ML(4) complex). The toxicity assessment established viable operation ranges (ca.

Adiabatic elimination-based coupling control in densely packed subwavelength waveguides.

The ability to control light propagation in photonic integrated circuits is at the foundation of modern light-based communication. However, the inherent crosstalk in densely packed waveguides and the lack of robust control of the coupling are a major roadblock toward ultra-high density photonic integrated circuits. As a result, the diffraction limit is often considered as the lower bound for ultra-dense silicon photonics circuits. Here we experimentally demonstrate an active control of the coupling between two closely packed waveguides via the interaction with a decoupled waveguide. This control scheme is analogous to the adiabatic elimination, a well-known procedure in atomic physics. This approach offers an attractive solution for ultra-dense integrated nanophotonics for light-based communications and integrated quantum computing.

Characterization of phenol and trichloroethene degradation by the rhizobium Ralstonia taiwanensis.

Ralstonia taiwanensis is a root nodule bacterium originally isolated from Mimosa sp. in southern Taiwan. Some strains of R. taiwanensis demonstrated the ability to grow on medium containing phenol as the sole carbon source, especially strain TJ86, which was able to survive and grow at phenol concentrations of up to 900 mg/l. The dependence of the phenol degradation rate on the phenol concentration can be described by Haldane's model with a low KS (the apparent half-saturation constant) of 5.46 microM and an extremely high KSI (the apparent inhibition constant) 9075 microM. The optimal phenol degradation rate was 61 micromol/min/g cell, which occurred at a phenol concentration of 228 microM. The phenol-limited growth kinetics of TJ86 by Andrews's model also followed a similar trend to that of phenol degradation, indicating the close links between phenol degradation and cell growth. Strain TJ86 also achieved 100 and 40% degradation for soil samples amended with 500 and 1000 microg phenol/g soil (dry weight) within 9 days, respectively. Moreover, strain TJ86 cometabolically degraded trichloroethene (TCE) after being cultivated with media containing phenol or m-cresol as the carbon substrate. The sequence of the large-subunit phenol hydroxylase (LmPH) gene obtained from TJ86 displayed high homology to that of other phenol-utilizing bacteria. Results from kinetic and phylogenetic analyses suggest that strain TJ86 most likely belongs to group I phenol-degrading bacteria which are considered to be efficient TCE degraders. It is proposed that the symbiotic relationship between rhizobia R. taiwanensis and its host plant Mimosa sp. may have the potential for rhizoremediation of aquatic and soil environments contaminated by phenol and TCE.

Spectrally selective chiral silicon metasurfaces based on infrared Fano resonances.

Metamaterials and metasurfaces represent a remarkably versatile platform for light manipulation, biological and chemical sensing, and nonlinear optics. Many of these applications rely on the resonant nature of metamaterials, which is the basis for extreme spectrally selective concentration of optical energy in the near field. In addition, metamaterial-based optical devices lend themselves to considerable miniaturization because of their subwavelength features. This additional advantage sets metamaterials apart from their predecessors, photonic crystals, which achieve spectral selectivity through their long-range periodicity. Unfortunately, spectral selectivity of the overwhelming majority of metamaterials that are made of metals is severely limited by high plasmonic losses. Here we propose and demonstrate Fano-resonant all-dielectric metasurfaces supporting optical resonances with quality factors Q>100 that are based on CMOS-compatible materials: silicon and its oxide. We also demonstrate that these infrared metasurfaces exhibit extreme planar chirality, opening exciting possibilities for efficient ultrathin circular polarizers and narrow-band thermal emitters of circularly polarized radiation.

Plasmonic nanolaser using epitaxially grown silver film.

A nanolaser is a key component for on-chip optical communications and computing systems. Here, we report on the low-threshold, continuous-wave operation of a subdiffraction nanolaser based on surface plasmon amplification by stimulated emission of radiation. The plasmonic nanocavity is formed between an atomically smooth epitaxial silver film and a single optically pumped nanorod consisting of an epitaxial gallium nitride shell and an indium gallium nitride core acting as gain medium. The atomic smoothness of the metallic film is crucial for reducing the modal volume and plasmonic losses. Bimodal lasing with similar pumping thresholds was experimentally observed, and polarization properties of the two modes were used to unambiguously identify them with theoretically predicted modes. The all-epitaxial approach opens a scalable platform for low-loss, active nanoplasmonics.

Self-assembled plasmonic nanoparticle clusters.

The self-assembly of colloids is an alternative to top-down processing that enables the fabrication of nanostructures. We show that self-assembled clusters of metal-dielectric spheres are the basis for nanophotonic structures. By tailoring the number and position of spheres in close-packed clusters, plasmon modes exhibiting strong magnetic and Fano-like resonances emerge. The use of identical spheres simplifies cluster assembly and facilitates the fabrication of highly symmetric structures. Dielectric spacers are used to tailor the interparticle spacing in these clusters to be approximately 2 nanometers. These types of chemically synthesized nanoparticle clusters can be generalized to other two- and three-dimensional structures and can serve as building blocks for new metamaterials.