Papers by Mehmet Emre Tasgin
An electron-positron (e − e +) pair is created in vacuum above a critical electric field strength... more An electron-positron (e − e +) pair is created in vacuum above a critical electric field strength Ecrt which is quite large in the laboratory scale. The photon, thus the field, annihilates in the pair creation process. Here, we question if the pair creation (at E = Ecrt) introduces a boundary condition in the electromagnetic state, e.g., similar to the one in angular or linear momentum. We show that introduction of such a reasonable condition yields approximately the well-known magnetic flux quanta which normally one obtains using different arguments.
An electron-positron (e − e +) pair is created in vacuum above a critical electric field strength... more An electron-positron (e − e +) pair is created in vacuum above a critical electric field strength Ecrt which is quite large in the laboratory scale. The photon, thus the field, annihilates in the pair creation process. Here, we question if the pair creation (at E = Ecrt) introduces a boundary condition in the electromagnetic state, e.g., similar to the one in angular or linear momentum. We show that introduction of such a reasonable condition yields approximately the well-known magnetic flux quanta which normally one obtains on different grounds.
We demonstrate effective background-free continuous wave nonlinear optical excitation of molecule... more We demonstrate effective background-free continuous wave nonlinear optical excitation of molecules that are sandwiched between asymmetrically constructed plasmonic gold nanoparticle clusters. Near infrared photons are converted to visible plasmon oscillations through efficient plasmonic second harmonic generation. Molecules absorb the visible plasmons and fluoresce. 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.
We show that, nonlinear optical processes of nanoparticles can be controlled by the presence of i... more 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.
We show that second harmonic generation can be enhanced by Fano resonant coupling of asymmetric p... more 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.
Physical Review A, 2015
We study the relation between the nonclassicality of single-mode Gaussian states and the twomode ... more We study the relation between the nonclassicality of single-mode Gaussian states and the twomode entanglement generated by those states via a beam splitter. The nonclassicality of a singlemode state is quantified in terms of the degree of squeezing. The two-mode entanglement is quantified as the difference between the input and the output nonclassicalities at a beam splitter, which is shown to be qualitatively equivalent to the logarithmic negativity. We derive a conservation relation between the nonclassicality of the two single-mode input states and the sum of two-mode entanglement and the output single-mode nonclassicality after a beam splitter. This conservation relation is extended to many sets of beam splitters.
Journal of Optics, 2015
We show that second harmonic generation can be enhanced by Fano resonant coupling of asymmetric p... more 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.
We investigate theoretically a topological vortex phase transition induced by a superradiant phas... more We investigate theoretically a topological vortex phase transition induced by a superradiant phase transition in an atomic Bose-Einstein condensate driven by a Laguerre-Gaussian optical mode. We show that superradiant radiation can either carry zero angular momentum, or be in a rotating Laguerre-Gaussian mode with angular momentum. The conditions leading to these two regimes are determined in terms of the width for the pump laser and the condensate size for the limiting cases where the recoil energy is both much smaller and larger than the atomic interaction energy.
The dynamics of a spinor BEC coupled magnetically to a high-Q mechanical membrane are studied the... more The dynamics of a spinor BEC coupled magnetically to a high-Q mechanical membrane are studied theoretically. In particular, we investigate the effects of using phase-contrast imaging to observe the spin of the BEC. In the case of highly dispersive measurements, the Larmor frequency of the BEC can be found to high precision, and the shift in this frequency provides useful information about the motion of the membrane. On the other hand, for projective spin measurements, a large back-action is induced in the membrane, allowing in some cases the production of non-classical states of motion. We investigate the possibilities for cooling and heating, the production of Fock and cat states, and probabilistic state control of the membrane in this latter case.
DESCRIPTION Enhancement and suppression of nonlinear processes in coupled systems of plasmonic co... more DESCRIPTION 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.
Journal of Optics, 2014
We show that, nonlinear optical processes in a plasmonic metal nanoparticle (MNP) dimer can be co... more We show that, nonlinear optical processes in a plasmonic metal nanoparticle (MNP) dimer can be controlled by the presence of a molecule or a quantum dot. (i) Frequency conversion can be suppressed if the dimer is coupled to a quantum object which is resonant to the generated frequency. This occurs simply because, EIT does not allow an excitation at the converted frequency frequency. (ii) On the contrary, a similar effect can be used to enhance the frequency conversion. Nonlinear processes can be brought to resonance without tuning the dimer modes. Path interference effect cancels the nonresonant frequency terms. Here, we consider the second harmonic generation (SHG) as an example to demonstrate the control mechanism. However, the method can be easily generalized to other nonlinear processes.
Nanoscale, 2013
We investigate the dynamics of the oscillations over a plasmonic nanometal when it is strongly co... more We investigate the dynamics of the oscillations over a plasmonic nanometal when it is strongly coupled to a quantum dot (quantum emitter). We show that life time of the plasmonic oscillations can be increased several orders of magnitude, upto the decay time of the quantum emitter. Regarding the solar cell applications, such an effect gives rise to several orders of magnitude enhanced light-matter interaction. Because, i) incident sun light is trapped for a much longer time in the plasmonic nanometals which are doped over the surface of the solar cell and ii) life time of the slow light propagation lengthens. The new duration for plasmonic polarization is limited with the phase-coherence time of the sun light. Such an enhancement occurs due to the emergence of a phenomenon analogous to electromagnetically induced transparency (EIT). Additionally, we exhibit a complementary effect: the decay time of an electronically excited quantum emitter is severely shortened due to the antenna coupling.
We show that single-mode nonclassicality of the output of an optomechanical cavity and the noncau... more 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.
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Papers by Mehmet Emre Tasgin