The electrocatalytic properties of nanoparticles depend on their size, shape and composition. These properties are typically probed by measuring the total electrocatalytic reaction current of a large number of nanoparticles, but this approach is time-consuming and can only measure the average catalytic activity of the nanoparticles under study. However, the identification of new catalysts requires the ability to rapidly measure the properties of nanoparticles synthesized under various conditions and, ideally, to measure the electrocatalytic activity of individual nanoparticles. Here, we show that a plasmonic-based electrochemical current-imaging technique can simultaneously image and quantify the electrocatalytic reactions of an array of 1.6 × 10(5) platinum nanoparticles printed on an electrode surface, which could facilitate high-throughput screening of the catalytic activities of nanoparticles. We also show that the approach can be used to image the electrocatalytic reaction current and measure the cyclic voltammograms of single nanoparticles.

Combining the advantages of ultrahigh photon emission rates achievable in the gap surface plasmon polaritons with high extraction decay rates into low-loss nanofibers, we demonstrate theoretically the efficient photon emission of a single dipole emitter and one-dimensional nanoscale guiding in metallic nanorod-coupled nanofilm structures coupled to dielectric nanofibers. We find that total decay rates and surface plasmon polariton channel decay rates orders of magnitude larger than those characteristic of metallic nanofilms alone can be achieved in ultrastrong hot spots of gap plasmons. For the requirement of practical applications, propagating single photons with decay rates of 290γ_{0}-770γ_{0} are guided into the phase-matched low-loss nanofibers. The proposed mechanism promises to have an important impact on metal-based optical cavities, on-chip bright single photon sources and plasmon-based nanolasers.

The mechanism of using the anisotropic Purcell factor to control the spontaneous emission linewidths in a four-level atom is theoretically demonstrated; if the polarization angle bisector of the two dipole moments lies along the axis of large/small Purcell factor, destructive/constructive interference narrows/widens the fluorescence center spectral lines. Large anisotropy of the Purcell factor, confined in the subwavelength optical mode volume, leads to rapid spectral line narrowing of atom approaching a metallic nanowire, nanoscale line width pulsing following periodically varying decay rates near a periodic metallic nanostructure, and dramatic modification on the spontaneous emission spectrum near a custom-designed resonant plasmon nanostructure. The combined system opens a good perspective for applications in ultracompact active quantum devices. KEYWORDS: Surface plasmon, spontaneous emission, Purcell factor, quantum emitter, quantum interference R ecent developments in nanotechnology and information technologies have made nanoscale light-matter interaction a tremendous research focus. 1 Small optical mode area in nanofiber-based photonic structures plays a significant role allowing low-light level quantum optical phenomena, such as electromagnetically induced transparency in the nanowatt regime, 2,3 four wave mixing with great gain, 4 and two-photon absorption with sharp peaks in the Rubidium vapor. 5 Ultrasmall optical mode volume in plasmon nanostructures 6 leads to strong coupling between surface plasmons and quantum emitters, which enables the vacuum Rabi splitting, 7,8 the Fano lineshapes in the absorption spectrum, 9−12 and its obvious influence on the two-photon statistics. 13 Superior to many available photonic nanostructures, associated with ultrasmall optical mode volume, 6 plasmonic structures present the key advantage of a large subwavelengthconfined anisotropic vacuum, that is, large anisotropic Purcell factor, 14,15 which originates from an anisotropic electric mode density of collective oscillations of free electrons in metals. 16−19 Another advantage is strong evanescent field of metallic nanostructures, which has promoted many applications, for example, SERS, 20 nanometer biosensors and waveguides, 21 nonlinear optical frequency mixing, 22−24 solar cell, 25,26 and so forth. Through modifying the population of excited states and decay rate of quantum emitters near plasmon structure, the fluorescence enhancement and quenching of fluorescent molecules and semiconductor quantum dots can be controlled well. 27−32 By confining the light into nanoscale volumes, plasmonic elements allow for a nanoscale realization of Mollow triplet of emission spectra and antibunching of emission photons of single molecules that traditional technique can not be accessible. 1,33,34 Through the nanoscale coupling between the surface plasmon modes and single quantum emitter, the directional and efficiency generation of single photons 17−19 and entanglement of two qubits 35 were proposed. These advantages, t...

Surface plasmons with ultrasmall optical mode volume and strong near field enhancement can be used to realize nanoscale light-matter interaction. Combining surface plasmons with the quantum system provides the possibility of nanoscale realization of important quantum optical phenomena, including the electromagnetically induced transparency (EIT), which has many applications in nonlinear quantum optics and quantum information processing. Here, using a custom-designed resonant plasmon nanocavity, we demonstrate polarized position-dependent linewidth-controllable EIT spectra at the nanoscale. We analytically obtain the double coherent population trapping conditions in a double-Λ quantum system with crossing damping, which give two transparent points in the EIT spectra. The linewidths of the three peaks are extremely sensitive to the level spacing of the excited states, the Rabi frequencies and detunings of pump fields, and the Purcell factors. In particular the linewidth of the central peak is exceptionally narrow. The hybrid system may have potential applications in ultra-compact plasmon-quantum devices.

Single photon emission from a collection of resonantly excited two-level atoms is an expanding field. Recent work has shown single photon superradiance from an extended ensemble yields enhanced directional spontaneous emission. This paper presents an operator which commutes with the observables R R , z 2 and breaks their degeneracy for the single photon states. Its eigenvectors are a unimodular basis for the single photon states. A simple scheme is given for writing out these states directly without iterative construction and without requiring recourse to Gram-Schmidt orthogonalization. A relatively simple scheme is proposed for experimental realization. In the final part of the paper the mathematical method is extended to generate cooperative states with smaller cooperativity number R.