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The use of Virtual Private Networks (VPNs) has witnessed an outstanding rise as they aim to provide confidentiality and anonymity to communication. Despite this enormous and ubiquitous usage, VPNs come with various security, misconfiguration, and performance related issues thereby hindering the users to take maximum advantage of this revolutionary technology. To address this concern, VPN users must choose the most secure and perfect VPN solution for the smooth functioning of daily life activities. Generally, no clear set of directions is available for assisting a common VPN user thereby accentuating the need to develop an elucidated and coherent checklist that thoroughly helps in evaluating any VPN based on its security, performance, auditing, and management function. This research comprehensively surveys VPN technologies, its features, working principles, and compliance principles that evolved over the last two decades. Based on it, this research presents a new methodology in the form of a feature-enriched template to comprehensively analyze a VPN solution. Each VPN feature is given its score against the potential damage it may cause in case of failure and the probability of occurrence of that failure. In this way, the corporate sector and individual users can quantitatively and qualitatively grade available options while choosing a VPN and use it effectively. [ABSTRACT FROM AUTHOR]

Spectra of the small Fabry–Perot interferometer (FPI) of the size of the order of the wavelength, with the main mode excited by a quantum field from a nano–LED or a laser, are investigated. The input field is detuned from the FPI mode with only a few photons. We formulate the convenient model for the FPI interacting with a quantum field, and provide novel explicit expressions for the field and the photon number fluctuation spectra inside and outside the FPI, with clearly identified contributions of the quantum and the classical noise. As a result, we found the spectra structures are quite different for the field, the photon number fluctuations inside the FPI, for the transmitted and the reflected fields and note asymmetries in spectra. The quantum noise is colored (or white) inside (or outside) the FPI, which explains differences in spectra. As another novel result, we calculate the second-order time auto–correlation functions for the FPI field; they oscillate and are negative under certain conditions. Results will help the study, design, manufacture, and use of the small elements of quantum optical integrated circuits, such as delay lines or optical transistors. [ABSTRACT FROM AUTHOR]

The hot electron generation in plasmonic nanoparticles is the key to efficient plasmonic photocatalysis. Here, the effect of Tamm states (TSs) at the metal–semiconductor interface on hot electron generation and Landau damping (LD) in metal nanoparticles is studied theoretically for the first time. TSs can lead to resonant hot electron generation and to the LD rate enhanced by several times. The resonant hot electron generation is reinforced by the transition absorption due to the jump of the permittivity at the metal–semiconductor interface. Since electron states in the metal and the quasi‐discrete TS are coupled coherently ("bound state in continuum"), the absorption spectrum of light by electrons has a Fano‐type shape. The results demonstrate clearly the importance of taking into account details of the semiconductor band structure and surface states at the metal–semiconductor interface, including Tamm surface states, for a proper description of the hot carrier generation and LD. The results are in correspondence with earlier experimental works on coherent electron transport and chemical‐induced damping in plasmonic nanostructures. Thus, by judicious selection of semiconductor materials with Tamm surface states one can engineer decay rates and hot carrier production for important applications, such as photodetection and photochemistry. [ABSTRACT FROM AUTHOR]

A laser model is formulated in terms of quantum harmonic oscillators. Emitters in the low lasing states are usual harmonic oscillators, and emitters in the upper states are inverted harmonic oscillators. Diffusion coefficients, consistent with the model and necessary for solving quantum nonlinear laser equations analytically, are found. Photon number fluctuations of the lasing mode and fluctuations of the population of the lasing states are calculated. Collective Rabi splitting peaks are predicted in the intensity fluctuation spectra of the superradiant lasers. Population fluctuation mechanisms in superradiant lasers and lasers without superradiance are discussed and compared with each other. [ABSTRACT FROM AUTHOR]

We investigate the surface photoemission (SPE) and the volume (VPE) photoemission from metal nanoparticles into semiconductor environments with a varied height of the potential barrier at the metal–semiconductor interface. We show that the internal quantum efficiency of the SPE becomes several times larger than the one of the VPE, when the barrier height decreases and the contact on the interface approaches to the ohmic one. Discontinuities in the electron effective mass and in dielectric functions at the interface are taken into account in the calculations. Results are important for efficient generation of hot electrons from metal nanostructures for such applications as photocatalysis and water splitting. [ABSTRACT FROM AUTHOR]

We observe anomalous visible to near-infrared electromagnetic emission from electrically driven atomic-size point contacts. We show that the number of photons released strongly depends on the quantized conductance steps of the contact. Counterintuitively, the light intensity features an exponential decay dependence with the injected electrical power. We propose an analytical model for the light emission considering an out-of-equilibrium electron distribution. We treat photon emission as a Bremsstrahlung process resulting from hot electrons colliding with the metal boundary, and find qualitative accord with the experimental data. [ABSTRACT FROM AUTHOR]

We propose an original concept for on-chip excitation and amplification of surface plasmon polaritons. Our approach, named nanoresotron, utilizes the collective effect of dissipative instability of a 2D direct current flowing in vicinity of a metal surface. The instability arises through the excitation of self-consistent plasma oscillations and results in the creation of a pair of collective surface electromagnetic modes in addition to conventional plasmon resonances. We derive the dispersion equations for these modes using self-consistent solutions of Maxwell's and 2D hydrodynamics equations. We find that the phase velocities of these new collective modes are close to the drift velocity of 2D electrons. We demonstrate that the slow mode is amplified while the fast mode exhibits absorption. Estimates indicate that very high gain are attainable, which makes the nanoresotron a promising scheme to electrically excite and regenerate surface plasmon polaritons. [ABSTRACT FROM AUTHOR]

We describe superradiance of a few emitters in a dissipative environment with nonradiative decay in the Schrödinger approach, which is simpler than the density matrix formalism. We find that superradiance increases the quantum efficiency of the radiation if the baths, responsible for dissipation, do not come to equilibrium. The reason is that decoherence destroys Dicke “dark” states, lets emitters radiate, and does not affect the fast radiation from “bright” Dicke states. [ABSTRACT FROM AUTHOR]

Transition absorption of a photon by an electron passing through a boundary between two media with different permittivities is described both classically and quantum mechanically. Transition absorption is shown to make a substantial contribution to photoelectron emission at a metal/semicon-ductor interface in nanoplasmonic systems, and is put forth as a possible microscopic mechanism of the surface photoelectric effect in photodetectors and solar cells containing plasmonic nanoparticles. [ABSTRACT FROM AUTHOR]

Nano‐mechanical oscillator (NMO) based on amorphous carbon nanowhisker (CNW) with nanotraps for resonant weighting of nanoparticles in range of mass (10−14–10−15) g is presented. NMO with nanotraps is fabricated on the top of tungsten tip using focused electron beam technique. For resonant weighting the gold nanospheres are captured under the exposure of an electron beam by nanotraps locate on the top of CNW. Jump of gold nanoparticle to the nanotrap and oscillations of CNW are visualized using scanning electron microscope (SEM). The NMO amplitude‐frequency characteristics are calculated via automated numerical analysis of the sequence of SEM images obtained during the oscillations frequency sweeping. In order to calibrate the resonance mass detector based on CNW with nanotrap the gold nanosphere with diameter of (170 ± 5) nm and mass of (49.6 ± 9.2) × 10−15 g is weighed in vacuum. The resonant mass detector (RMD) based on carbon nanowhiskers with traps for weighing nanoobjects is presented. The carbon nanostructures are created using additive technique in a scanning electron microscope. Mechanical traps can reliably fix nanoparticles. It is shown that one can determine the mass of the nanoparticles with a sufficiently high accuracy in the range of (10−14–10−15) g using RMD. [ABSTRACT FROM AUTHOR]