Raúl A. Bustos-Marún

Buffering plasmons in nanoparticle waveguides at the virtual-localized transition

We study the plasmonic energy transfer from a locally excited nanoparticle (LE-NP) to a linear array of small NPs and we obtain the parametric dependence of the response function. An analytical expression allows us to distinguish the extended resonant states and the localized ones, as well as an elusive regime of virtual states. This last appears when the resonance width collapses and before it becomes a localized state. Contrary to common wisdom, the highest excitation transfer does not occur when the system has a well defined extended resonant state but just at the virtual-localized transition, where the main plasmonic modes have eigenfrequencies at the passband edge. The slow group velocity at this critical frequency enables the excitation buffering and hence favors a strong signal inside the chain. A similar situation should appear in many other physical systems. The extreme sensitivity of this transition to the waveguide and LE-NP parameters provides new tools for plasmonics.

Dynamical regimes of a quantum SWAP gate beyond the Fermi golden rule

We discuss how the baths memory affects the dynamics of a SWAP gate. We present an exactly solvable model that shows various dynamical transitions when treated beyond the Fermi golden rule. By moving continuously a single parameter, the unperturbed Rabi frequency, we sweep through different analytic properties of the density of states: (I) collapsed resonances that split at an exceptional point in (II) two resolved resonances; (III) out-of-band resonances; (IV) virtual states; and (V) pure point spectrum. We associate them with distinctive dynamical regimes: overdamped, damped oscillations, environment controlled quantum diffusion, anomalous diffusion, and localized dynamics, respectively. The frequency of the SWAP gate depends differently on the unperturbed Rabi frequency. In region I there is no oscillation at all, while in the regions III and IV the oscillation frequency is particularly stable because it is determined by the environments band width. The anomalous diffusion could be used as a signature for the presence of the elusive virtual states.

Decoherence in current induced forces: Application to adiabatic quantum motors

Fil: Fernandez, Lucas Jonatan. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Instituto de Fisica Enrique Gaviola. Universidad Nacional de Cordoba. Instituto de Fisica Enrique Gaviola; Argentina. Universidad Nacional de Cordoba. Facultad de Matematica, Astronomia y Fisica; Argentina

Dynamics and decoherence in nonideal Thouless quantum motors

Fil: Fernandez, Lucas Jonatan. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Instituto de Fisica Enrique Gaviola. Universidad Nacional de Cordoba. Instituto de Fisica Enrique Gaviola; Argentina

Real-time diagrammatic approach to current-induced forces: Application to quantum-dot based nanomotors

During the last years there has been an increasing excitement in nanomotors and particularly in current-driven nanomotors. Despite the broad variety of stimulating results found, the regime of strong Coulomb interactions has not been fully explored for this application. Here we consider nanoelectromechanical devices composed by a set of coupled quantum dots interacting with mechanical degrees of freedom taken in the adiabatic limit and weakly coupled to electronic reservoirs. We use a real-time diagrammatic approach to derive general expressions for the current-induced forces, friction coefficients, and zero-frequency force noise in the Coulomb blockade regime of transport. We prove our expressions accomplish with Onsagers reciprocity relations and the fluctuation-dissipation theorem for the energy dissipation of the mechanical modes. The obtained results are illustrated in a nanomotor consisting of a double quantum dot capacitively coupled to some rotating charges. We analyze the dynamics and performance of the motor as function of the applied voltage and loading force for trajectories encircling different triple points in the charge stability diagram.

Plasmonic graded-chains as deep-subwavelength light concentrators

We have studied the plasmonic properties of aperiodic arrays of identical nanoparticles (NPs) formed by two opposite and equal graded-chains (a chain where interactions change gradually). We found that these arrays concentrate the external electromagnetic fields even in the long wavelength limit. The phenomenon was understood by identifying the system with an effective cavity where plasmonics excitations are trapped between effective band edges, resulting from the change of passband with the NPs position. Dependence of excitation concentration on several system parameters was also assessed. This includes different gradings as well as NP couplings, damping, and resonant frequencies. In the spirit of the scaling laws in condensed matter physics, we developed a theory that allows us to rationalize all these system parameters into universal curves. The theory is quite general and can also be used in many other situations (different arrays for example). Additionally, we also provided an analytical solution, in the tight-binding limit, for the plasmonic response of homogeneous linear chains of NPs illuminated by a plane wave. Our results can find applications in sensing, near field imaging, plasmon-enhanced photodetectors, as well as to increase solar cell efficiency.

Tailoring Optical Fields Emitted by Subwavelength Nanometric Sources

In this work, we study a simple way of controlling the emitted fields of subwavelength nanometric sources. The system studied consists of arrays of nanoparticles (NPs) embedded in optical active media. The key concept is the careful tuning of NP’s damping factors, which changes the eigenmode’s decay rates of the whole array. This inevitably leads, at long time, to a locking of relative phases and frequencies of individual localized-surfaces-plasmons (LSPs) and, thus, controls the emitted field. The amplitude of the LSP’s oscillations can be kept constant by embedding the system in optical active media. In the case of full loss compensation, this implies that not only the relative phases, but also the amplitudes of the LSPs remain fixed, leading us, additionally, to interpret the process as a new example of synchronization. The proposed approach can be used as a general way of controlling and designing the electromagnetic fields emitted by nanometric sources, which can find applications in optoelectronic, nanoscale lithography, and probing microscopy.

Excitation-Transfer Plasmonic Nanosensors Based on Dynamical Phase Transitions

Dynamical phase transitions (DPTs) describe the abrupt change in the dynamical properties of open systems when a single control parameter is slightly modified. Recently, we found that this phenomenon is also present in a simple model of a linear array of metallic nanoparticles in the form of a localized–delocalized DPT. In this work we show how to take advantage of DPTs to design a new kind of plasmonic sensor which should own some unique characteristics. For example, if it were used as a plasmon ruler, it would not follow the so-called universal plasmon ruler equation [Nano Letters2007, 7, 2080–2088], exhibiting instead an on–off switching feature. This basically means that a signal should be observed only when the control/measured parameter, that is, a distance in the case of plasmon rulers, has a very precise and predetermined value. Here, we demonstrate their feasibility and unique characteristics, showing that they combine high sensitivity with this on–off switching feature in terms of different dist...