arXiv subjects

Mehmet Emre Tasgin

Publications and source records attributed to Mehmet Emre Tasgin.

51 records · Page 3Linked to original sources

arXiv2018

Fano enhancement of SERS signal without increasing the hot spot intensity

Plasmonic nanostructures enhance nonlinear response, such as surface enhanced Raman scattering (SERS), by localizing the incident field into hot spots. The localized hot spot field can be enhanced even further when linear Fano resonances (FR) take place in a double resonance scheme. However, hot spot enhancement is limited with the modification of the vibrational modes, the break-down of the molecule and the tunnelling regime. Here, we present a method which can circumvent these limitations. Our analytical model and solutions of 3D Maxwell equations show that: enhancement due to the localized field can be multiplied by a factor of $10^2$ to $10^3$. Moreover, this can be performed without increasing the hot spot intensity which also avoids the modification of the Raman modes. Unlike linear Fano resonances, we create a path interference in the nonlinear response. We demonstrate on a single equation that enhancement takes place due to cancellation of the contributing terms in the denominator of the SERS response.

physics.optics↗

arXiv2018

Controlling steady-state second harmonic signal via linear and nonlinear Fano resonances

Nonlinear signal even from a single molecule becomes visible at hot spots of plasmonic nanoparticles. In these structures, Fano resonances can control the nonlinear response in two ways. \textit{(i)} A linear Fano resonance can enhance the hot spot field, resulting enhanced nonlinear signal. \textit{(ii)} A nonlinear Fano resonance can enhance the nonlinear signal without enhancing the hot spot. In this study, we compare the enhancement of second harmonic signal at the steady-state obtained via these two methods. Since we are interested in the steady-state signal, we adapt a linear enhancement which works at the steady-state. This is different than the dark-hot resonances that appears in the transparency window due to enhanced plasmon lifetime.

physics.optics↗

arXiv2016

Many-particle entanglement criterion for superradiant-like states

We derive a many-particle inseparability criterion for mixed states using the relation between single-mode and many-particle nonclassicalities. It works very well not only in the vicinity of the Dicke states, but also for the superposition of them: superradiant ground state of finite/infinite number of particles and time evolution of single-photon superradiance. We also obtain a criterion for ensemble-field entanglement which works fine for such kind of states. Even though the collective excitations of the many-particle system is sub-Poissonian --which results in entanglement-- the wave function displays bunching.

quant-ph↗

arXiv2016

Fluorescence Excitation by Enhanced Plasmon Upconversion under Continuous Wave Illumination

We demonstrate effective background-free continuous wave nonlinear optical excitation of molecules that are sandwiched between asymmetrically constructed plasmonic gold nanoparticle clusters. We observe that near infrared photons are converted to visible photons through efficient plasmonic second harmonic generation. Our theoretical model and simulations demonstrate that Fano resonances may be responsible for being able to observe nonlinear conversion using a continuous wave light source. We show that nonlinearity enhancement of plasmonic nanostructures via coupled quantum mechanical oscillators such as molecules can be several orders larger as compared to their classical counterparts.

physics.optics↗

arXiv2016

Collectively induced many-vortices topology via rotatory Dicke quantum phase transition

We examine the superradiance of a Bose-Einstein condensate pumped with a Laguerre-Gaussian laser of high winding number, e.g., $\ell = 7$. The laser beam transfers its orbital angular momentum (OAM) to the condensate at once due to the collectivity of the superradiance. An $\ell$-fold rotational symmetric structure emerges with the take place of rotatory superradiance. $\ell$ number of single-charge vortices appear at the arms of this structure. Even though the pump and the condensate profiles initially have cylindrical symmetry, we observe that it is broken to $\ell$-fold rotational symmetry during the superradiance. Breaking of the cylindrical symmetry into the $\ell$-fold symmetry and OAM transfer to the BEC become possible after the same critical pump strength. Reorganization of the condensate resembles the ordering in the experiment by Esslinger and colleagues [Nature, {\bf 264}, 1301 (2010)]. We show that the critical point for the onset of the reorganization follows the form of the Dicke quantum phase transition.

cond-mat.quant-gas↗

arXiv2015

Enhanced Second Harmonic Generation from Coupled Asymmetric Plasmonic Metal Nanostructures

We show that second harmonic generation can be enhanced by Fano resonant coupling of asymmetric plasmonic metal nanostructures. We develop a theoretical model examining the effects of electromagnetic interaction between two metal nanostructures on the second harmonic generation. We compare the second harmonic generation efficiency of a single plasmonic metal nanostructure with that of two coupled ones. We show that second harmonic generation from a single metal nanostructure can be enhanced about 30 times by attaching a second metal nanostructure with a 10 times higher quality factor than that of the first one. The origin of this enhancement is Fano resonant coupling of the two metal nanostructures. We support our findings on Fano enhancement of second harmonic generation by an experimental study of a coupled plasmonic system composed of a silver nanoparticle and a silver nanowire on glass surface in which the ratio of the quality factors are also estimated to be around 10 times.

physics.optics↗

arXiv2015

Conservation relation of nonclassicality and entanglement for Gaussian states in a beam-splitter

We study the relation between single-mode nonclassicality and two-mode entanglement in a beam-splitter. We show that not all of the nonclassicality (entanglement potential) is transformed into two-mode entanglement for an incident single-mode light. Some of the entanglement potential remains as single-mode nonclassicality in the two entangled output modes. Two-mode entanglement generated in the process can be equivalently quantified as the increase in the minimum uncertainty widths (or decrease in the squeezing) of the output states compared to the input states. We use the nonclassical depth and logarithmic negativity as single-mode nonclassicality and entanglement measures, respectively. We realize that a conservation relation between the two quantities can be adopted for Gaussian states, if one works in terms of uncertainty width. This conservation relation is extended to many sets of beam-splitters.

quant-ph↗

arXiv2015

A method for achieving larger enhancement in Four-Wave Mixing via plasmonic path interference effects

Enhancement and suppression of nonlinear processes in coupled systems of plasmonic converters and quantum emitters are well-studied theoretically, numerically and experimentally, in the past decade. Here, in difference, we explicitly demonstrate --with a single equation-- how the presence of a Fano resonance leads to cancellation of nonresonant terms in a four-wave mixing process. Cancellation in the denominator gives rise to enhancement in the nonlinearity. The explicit demonstration, we present here, guides us to the method for achieving more and more orders of magnitude enhancement factors via path interference effects. We also study the coupled system of a plasmonic converter with two quantum emitters. We show that the potential for the enhancement increases dramatically due to better cancellation of the terms in the denominator.

physics.optics↗

arXiv2015

Enhancement and Suppression of Four wave mixing in coupled semiconductor quantum dot-gold grating systems

We show that, Four wave mixing (FWM) processes of grating can be controlled by the presence of interactions with a quantum dot or a molecule made by coupled quantum dots. By choosing the appropriate level spacing for the quantum emitter, one can either suppress or enhance the Four wave mixing process. We revel theoretically the underlying mechanism for this effect. (i) Suppression in FWM intensity occurs simply because induced Electromagnetic Induced Transparency does not allow the excitation at converted FWM frequency. (ii) Enhancement emerges since FWM process can be brought to resonance. Path interference effect cancels the nonresonant frequency terms. Furthermore, we have also shown that in case of coupled quantum dots enhancement increases significantly as compared to the case of a single quantum dot.

quant-ph↗

arXiv2015

Mutual emergence of noncausal optical response and nonclassicality in an optomechanical system

We show that single-mode nonclassicality of the output of an optomechanical cavity and the noncausal linear optical response of this cavity emerge at the same critical cavity-mechanical coupling. In other words, single-mode nonclassicality emerges when the barrier (in electromagnetism) avoiding faster-than-light communication is lifted off. The nature of the emergence of noncausal behavior does not depend on the length (boundary conditions) and the type of the cavity. Origin of the noncausal behavior is the temporal/frequency relations between the incident and reflected waves at the outer surface of the cavity. We further discuss the relations with the recent studies; (i) equivalence of the entanglement among identical particles to the nonclassicality of their quasiparticle excitations, (ii) necessity of superfluid behavior of vacuum, and (iii) entanglement-wormhole equivalence.

quant-ph↗

arXiv2014

Engineering nonlinear response of nanomaterials using Fano resonances

We show that, nonlinear optical processes of nanoparticles can be controlled by the presence of interactions with a molecule or a quantum dot. By choosing the appropriate level spacing for the quantum emitter, one can either suppress or enhance the nonlinear frequency conversion. We reveal the underlying mechanism for this effect, which is already observed in recent experiments: (i) Suppression occurs simply because transparency induced by Fano resonance does not allow an excitation at the converted frequency. (ii) Enhancement emerges since nonlinear process can be brought to resonance. Path interference effect cancels the nonresonant frequency terms. We demonstrate the underlying physics using a simplified model, and we show that the predictions of the model are in good agreement with the 3-dimensional boundary element method (MNPBEM toolbox) simulations. Here, we consider the second harmonic generation in a plasmonic converter as an example to demonstrate the control mechanism. The phenomenon is the semi-classical analog of nonlinearity enhancement via electromagnetically induced transparency.

cond-mat.mes-hall↗

arXiv2014

Divergent nonlinear optical response of three resonator system via Fano resonances

In a previous study, we have discovered that nonlinear processes can be enhanced several orders of magnitude due to the path interference effects which are introduced by Fano resonances. Emergence of this phenomenon has been demonstrated also in 3-dimensional solutions of Maxwell equations. However, enhancement has been found to be limited by the decay rate of the plasmonic oscillations. In the present work, we demonstrate that such a limitation can be lifted o? when the path interference from two quantum emitters to a plasmonic resonator (second harmonic converter) is considered. Enhancement factors much larger than 7 orders of magnitude are possible using such an interference scheme. Therefore, a single hybridized system of 3 particles (manufactured carefully) can account for almost all of the second harmonic generated radiation emitted from a sample of plasmonic particle clusters decorated with quantum emitters (e.g. a spaser).

quant-ph↗

arXiv2013

Metal nanoparticle plasmons operating within quantum lifetime

We investigate the dynamics of a plasmonic oscillation over a metal nanoparticle when it is strongly coupled to a quantum emitter (e.g. quantum dot, molecule). We simulate the density matrix evolution for a simple model; coupled classical--quantum oscillators system. We show that lifetime of the plasmonic oscillations can be increased several orders of magnitude, upto the decay time of the quantum emitter. This effect shows itself as the narrowing of the plasmon emission band in the spaser (surface plasmon amplification by stimulated emission of radiation) experiment [{\it Nature}, {\bf 2009}, 460, 1110], where a gold nanoparticle interacts with the surrounding molecules. Enhancement of the plasmonic excitation lifetime enables stimulated emission to overcome the spontaneous one. The enhancement occurs due to the emergence of a phenomenon analogous to electromagnetically induced transparency (EIT). The effect can find applications in many areas of nanoscale physics, such as in quantum information with plasmons and in increasing solar cell efficiency.

physics.optics↗

arXiv2012

Testing the reliability of a velocity definition in dispersive medium

We introduce a method to test if a given velocity definition corresponds to an actual physical flow, when the pulse propagation in dispersive medium is considered. i) We calculate the mean arrival time between two positions in space, using the Fourier expansion in real-ωspace. ii) We calculate the mean spatial displacement between two points in time, using the Fourier expansion in real-k space. We compare the velocities calculated in the two approaches. If the velocity definition truly corresponds to an actual flow, the two velocities must be the same. However, we show that the two velocities differ significantly (4%) in the region of superluminal propagation even for the successful definition introduced by Peatross et al. [Phys. Rev. Lett. 84, 2370 (2000)].

physics.optics↗

arXiv2011

Spin Squeezing with Coherent Light via Entanglement Swapping

We analyze theoretically a scheme that produces spin squeezing via the continuous swapping of atom-photon entanglement into atom-atom entanglement, and propose an explicit experimental system where the necessary atom-field coupling can be realized. This scheme is found to be robust against perturbations due to other atom-field coupling channels.

quant-ph↗