Do Cloaked Objects Really Scatter Less?

We discuss the global scattering response of invisibility cloaks over the entire frequency spectrum, from static to very high frequencies. Based on linearity, causality and energy conservation we show that the total extinction and scattering, integrated over all wavelengths, of any linear, passive, causal and non-diamagnetic cloak necessarily increases compared to the uncloaked case. In light of this general principle, we provide a quantitative measure to compare the global performance of different cloaking techniques and we discuss solutions to minimize the global scattering signature of an object using thin, superconducting shells. Our results provide important physical insights on how invisibility cloaks operate and affect the global scattering of an object, suggesting ways to defeat countermeasures aimed at detecting cloaked objects using short impinging pulses.Comment: 29 pages, 4 figure

Invisibility and Cloaking: Origins, Present, and Future Perspectives

The development of metamaterials, i.e., artificially structured materials that interact with waves in unconventional ways, has revolutionized our ability to manipulate the propagation of electromagnetic waves and their interaction with matter. One of the most exciting applications of metamaterial science is related to the possibility of totally suppressing the scattering of an object using an invisibility cloak. Here, we review the available methods to make an object undetectable to electromagnetic waves, and we highlight the outstanding challenges that need to be addressed in order to obtain a fully functional coating capable of suppressing the total scattering of an object. Our outlook discusses how, while passive linear cloaks are fundamentally limited in terms of bandwidth of operation and overall scattering suppression, active and/or nonlinear cloaks hold the promise to overcome, at least partially, some of these limitations.AFOSR Award FA9550-13-1-0204NSF CAREER Award ECCS-0953311DTRA YIP Award HDTRA1-12-1-0022Electrical and Computer Engineerin

Multi-Layered Plasmonic Covers for Comb-Like Scattering Response and Optical Tagging

We discuss the potential of multilayered plasmonic particles to tailor the optical scattering response. The interplay of plasmons localized in thin stacked shells realizes peculiar degenerate cloaking and resonant states occurring at arbitrarily close frequencies. These concepts are applied to realize ultrasharp comb-like scattering responses and synthesize staggered, ideally strong super-scattering states closely coupled to invisible states. We demonstrate robustness to material losses and to variations in the background medium, properties that make these structures ideal for optical tagging.Comment: 15 pages, 4 figure

Relationships and the availability of credit to New Small Firms

We analyze the loans that startup firms obtain from banks by testing our predictions on a set of small, young Italian companies founded during the 1992-2004 period. According to our investigation, the amount of borrowing is determined by (1) the size of the firm, (2), the ability to offer collateral (3) perceived risk. Contrary to expectations, however, the length of the relationship with the lender has a weak influence.

High intrinsic energy resolution photon number resolving detectors

Transition Edge Sensors (TESs) are characterized by the intrinsic figure of merit to resolve both the energy and the statistical distribution of the incident photons. These properties lead TES devices to become the best single photon detector for quantum technology experiments. For a TES based on titanium and gold has been reached, at telecommunication wavelength, an unprecedented intrinsic energy resolution (0.113 eV). The uncertainties analysis of both energy resolution and photon state assignment has been discussed. The thermal properties of the superconductive device have been studied by fitting the bias curve to evaluate theoretical limit of the energy resolution