Josephson junction microwave amplifier in self-organized noise compression mode

The fundamental noise limit of a phase-preserving amplifier at frequency is the standard quantum limit . In the microwave range, the best candidates have been amplifiers based on superconducting quantum interference devices (reaching the noise temperature at 700 MHz), and non-degenerate parametric amplifiers (reaching noise levels close to the quantum limit at 8 GHz). We introduce a new type of an amplifier based on the negative resistance of a selectively damped Josephson junction. Noise performance of our amplifier is limited by mixing of quantum noise from Josephson oscillation regime down to the signal frequency. Measurements yield nearly quantum-limited operation, at 2.8 GHz, owing to self-organization of the working point. Simulations describe the characteristics of our device well and indicate potential for wide bandwidth operation

Taking plasmonic core-shell nanoparticles toward laser threshold

The first experimental demonstration of lasing plasmonic nanoparticles in 2009 ignited interest in active plasmonic structures with optical gain. However, the understanding of lasing in plasmonic nanoparticles is largely incomplete, and even less is known about their characteristics as they are taken toward the lasing threshold. Here we present a computational method and predictions of the lasing wavelength and threshold gain for spherical core-shell nanostructures with a metal core and a gain medium in the shell. We demonstrate that light scattering provides a simple diagnostics method to establish how far a specific nanoparticle is from reaching the lasing threshold. We also show that these structures can enhance the electric field by a factor of over 1500 (at 99.9% of threshold gain) and beyond, taking biosensing with these "smart dust" nanoparticles into the single molecule sensitivity regime.6 page(s

Extreme sensitivity of the optical properties of metal nanostructures to minor variations in geometry is due to highly localized electromagnetic field modes

Optical extinction of silver nanostructures produced by electron beam lithography has been modeled by a finite element method. While the simulations of the design geometry produce results that are markedly at odds with the experiment, subtle variations of the shape, such as rounding of structure edges, are able to bring the simulations in agreement with experiment. We present the effect of various aspects of structure geometry on the evolution of electromagnetic field modes. They are highly localized at the sharp edges and sides and strongly affected by minor shape variations such as edge rounding. This work demonstrates that optical absorption/extinction provides a simple and sensitive indication of subtle morphology features in metal nanostructures.7 page(s

Simultaneous concentration and separation of proteins in a nanochannel

Balancing the forces: Conductivity gradient focusing in a nanochannel achieves simultaneous separation and concentration of proteins without a temperature gradient, membrane, matrix, ampholytes, or external pump. The electrophoretic force (see picture; red arrow) that dominates at the low-salt side (-) balances the electro-osmotic force (blue) at the high-salt side (+).5 page(s