Nanoscale Electromagnetic Compatibility: Quantum Coupling and Matching in Nanocircuits

AcceptedArticle in PressThe paper investigates two typical electromagnetic compatibility (EMC) problems, namely, coupling and matching in nanoscale circuits composed of nano-interconnects and quantum devices in entangled state. Nano-interconnects under consideration are implemented by using carbon nanotubes or metallic nanowires (NWs), while quantum devices by semiconductor quantum dots. Equivalent circuits of such nanocircuits contain additional elements arising at nanoscale due to quantum effects. As a result, the notions of coupling and impedance matching are reconsidered. Two examples are studied: in the first one, electromagnetically coupled NWs are connected to classical lumped devices; in the second one, electromagnetically uncoupled transmission lines are terminated on quantum devices in entangled states. In both circuits, the EMC features qualitatively and quantitatively differ from their classical analogs. In the second example, we demonstrate the existence of quantum coupling, due to the entanglement, which exists in spite of the absence of classical electromagnetic coupling. The entanglement also modifies the matching condition introducing a dependence of the optimal value of load impedance on the line length

Quantum dot lattice as nano-antenna for collective spontaneous emission

\u3cp\u3eWe present a theory for the collective spontaneous emission of timed Dicke states in a periodic 2D-array of quantum dots (QDs) coupled by dipoledipole (d-d) interactions. The master equation is first reformulated with respect to the timed Dicke basis. As a result, we obtain simple analytical relations for the spontaneous decay rate, collective Lamb shift and radiative pattern. The collective spontaneous emission in QD-array manifests itself in strong directivity, whereby the radiative pattern consists of a set of strong radiative lobes. The direction of the first lobe is dictated by the pumping direction, while the other lobes correspond to diffractive rays due to the periodicity. The influence of d-d interactions on the radiation decay of timed Dicke states in QD arrays is identical to the influence of an environment to single-particle excited states similar to the action of a structured photonic reservoir. For a rectangular 2D-array, the equivalent structured photonic reservoir has a form of a hollow rectangular waveguide with perfectly conductive walls. For lattice periods comparable to the radiation wavelength the decay rate shows sharp peaks due to Van-Hove singularities in the photonic density of states (PDOS) similar to the Purcell effect in photonic crystals. The optical nanoantenna under study allows tuning of the radiation pattern by varying the timing.\u3c/p\u3

Integral equation technique for scatterers with mesoscopic insertions: Application to a carbon nanotube

We present the electromagnetic scattering theory for a finite-length nanowire with an embedded mesoscopic object. The theory is based on a synthesis of the integral equation technique of classical electrodynamics and the quantum transport formalism. We formulate Hallén-type integral equations, where the canonical integral operators from wire antenna theory are combined with special terms responsible for the mesoscopic structure. The theory is applied to calculate the polarizability of a finite-length single-walled carbon nanotube (CNT) with a short low-conductive section (LCS) in the microwave and subterahertz ranges. The LCS is modeled as a multichannel two-electrode mesoscopic system. The effective resistive sheet impedance boundary conditions for the scattered field are applied on the CNT surface. It is shown that the imaginary part of the polarizability spectrum has three peaks. Two of them are in the terahertz range, while the third is in the gigahertz range. The polarizability spectrum of the CNT with many LCSs has only one gigahertz peak, which shifts to low frequencies as the number of LCSs increases. The physical nature of these peaks is explained, and potential applications of nanoantennas are proposed