arXiv subjects

Mehmet Gunay

Publications and source records attributed to Mehmet Gunay.

8 recordsLinked to original sources

arXiv2026

All-optical switching of continuous-variable entanglement in an absorption-suppressed plasmonic nanodimer

A subwavelength quantum-photonic circuit element should simultaneously generate nonclassical light, suppress plasmonic loss, and remain dynamically tunable. We show that an orthogonal plasmonic nanorod dimer can satisfy all three requirements. A phase-locked control polarization induces plasmonic refractive-index enhancement, driving the probe response toward a near-zero-extinction regime while simultaneously tuning the local second-harmonic parametric interaction. The resulting nonlinear plasmonic source operates in an absorption-suppressed regime and enables all-optical control of quantum correlations. We demonstrate switchable logarithmic negativity and single-mode nonclassicality, establishing a route toward actively tunable quantum-plasmonic circuit elements operating well below the diffraction limit.

quant-ph↗

arXiv2025

Active tuning of ENZ resonances in meta-antenna through phase modulation of optical pulse

Plasmonic nanoantennas offer new avenues to manipulate the propagation of light in materials due to their near field enhancement and ultrafast response time. Here we investigate the epsilon-near-zero (ENZ) response in an L-shaped nanoantenna structure under the phenomenon of plasmonic analog of enhancement in the index of refraction. Using a quantum mechanical approach, we analyze the modulation in the response of probe field and emergence of ENZ frequency region both in the linear and nonlinear plasmonic system. We also demonstrate the active tuning of ENZ frequency region in a nanoantenna structure by modulating the phase of control pulse. The analytical and 3D FDTD simulation results show a significant spectral shift in the ENZ modes. Our proposed method offers the possibility to design and control optical tunable ENZ response in plasmonic metasurfaces without the use of ENZ material. Such metasurfaces can be used in on-chip photonic integrated circuits, further localization of incident fields, slow light operations and various quantum technologies.

physics.app-ph↗

arXiv2025

Optically tunable linear and nonlinear enhancement of index of refraction

Control of optical properties of materials by tuning their refractive index can revolutionize the current state-of-the-art technology to manipulate light propagation in the high loss media. Here we demonstrate active optical tuning of the plasmonic analog of \textit{enhancement of index of refraction} (EIR) in both linear and nonlinear regimes using a quantum mechanical approach. By employing a pump-probe scheme, we investigate the tuning of refractive index of the probe field by varying amplitude and phase of the pump source. In contrast to classical approach used in \cite{Panahpour2019}, we formulate both first- and second-order quantization to analyze nonlinear enhancement in the refractive index by modulating the response function of probe field. This approach enables indirect tuning of nonlinear modes and coherent control of the probe pulse under the coupling of linear plasmonic modes supported by two L-shaped nano-ellipsoids. Varying the pump amplitude not only shows a significant enhancement in the EIR in both regimes but also effectively suppresses optical losses with zero dispersion at the system's resonance frequency. Additionally, tuning pump phase induces a spectral shift in the frequency of the probe field which open new ways for active tuning of epsilon-near-zero (ENZ) materials. Our approach offers all-optical tuning of nonlinear refractive index which is essential for quantum technological applications. It also provides coherent control of optical properties of plasmonic nanostructures with applications in loss-compensated propagation and zero-index to high-refractive-index plasmonic metamaterials, as well as photonic switches.

physics.optics↗

arXiv2023

Environmental-induced work extraction

A local measurement extracts work as a backaction, e.g., in a system of two entangled cavities: first cavity, $a$, comprises a piston and the measurement is carried out on the second cavity, $b$. When no one makes a measurement on the cavity $b$, i.e., it is simply placed in vacuum; environmental monitoring results in the coherent states as the einselected pointer states (the measurement basis) [PRL 70, 1187 (1993)]. This makes the measurement, that nature itself performs, a Gaussian one with a fixed strength $λ=1$. We show that this makes nature assign a \textit{fixed} amount of work to a particular entanglement degree $0\leq ξ(r) \leq 1$, i.e., $W=ξ(r)\times(\bar{n}\hbarω_a)$, nothing that the term in parenthesis is the entire thermal energy. Afterwards, we show that this phenomenon applies quite generally, i.e, not restricted to a two-cavities system. We also touch on the influence of inherited symmterization entanglement in this context. We can arrive an additional phenomenon by considering that work is simply the process of converting randomly moving microscopic ingredients~(vanishing mean-velocity) into a directional one, i.e, with a nonzero mean-velocity. We show that such a change in the character of the motion introduces curvature in spacetime according to general relativity. This phenomenon is the first demonstration of a quantitative relation between entanglement and curvature using solely the quantum optics arguments.

quant-ph↗

arXiv2021

Fano enhancement of second harmonic field via dark-bright plasmon coupling

Surface plasmon resonances, the coherent oscillation of free electrons, can concentrate incident field into small volumes much smaller than the incident wavelength. The intense fields at these \textit{hot spots} enhance the light-matter interactions and may lead to the appearance of nonlinearity. Controlling such nonlinearities is significant for various practical applications. Here we report that by coupling dark modes to the first and the generated second harmonic modes separately, one can gain control over both fields. We find that by engineering path interferences (Fano resonances) between bright and dark plasmon modes it is possible to enhance the fundamental mode without increasing the nonlinear field, enhance the nonlinear field without modifying the fundamental mode, and enhance the second harmonic field with enhanced fundamental mode.

physics.optics↗

arXiv2020

Enhanced spontaneous down-conversion in a nonlinear crystal embedded with plasmonic-quantum emitter hybrid structures

Control of nonlinear response of nanostructures via path interference effects, i.e. Fano resonances, has been studied extensively. In such materials, a frequency conversion process which takes place near a hot spot has been considered. Here, we study a different case. The frequency conversion process takes place along the body of a nonlinear crystal. Metal nanoparticle-quantum emitter dimers control the down-conversion process, taking place throughout the crystal body, via introducing interfering conversion paths. Dimers behave as interaction centers. We show that a 2 order of magnitude enhancement is possible, beyond an enhancement due to localization effects. This factor multiplies the enhancement taking place due to the field localization.

physics.optics↗

arXiv2019

Ultra-high resolution aSNOM imaging at off-resonant wavelengths

An atomic force microscope~(AFM) tip, with a few nm-thick noble metal coating, gives rise to strong electric-field at the near-field of tip apex, i.e. hot spot, when illuminated with a beam of light linearly polarized in the axial direction. This strong near-field enables resolving molecular landscape or nano-scale defects on crystal surfaces in apertureless scanning near field optical microscopy or tip enhanced Raman spectroscopy applications. However, strong near fields appear only at certain illumination wavelengths at which material and geometry dependent plasmon resonances take place. Once the metal coated tip is manufactured, optimal operation wavelength remains fixed since the material and geometry of the tip apex remains fixed. Here, we show for the first time a method which renders an AFM tip useful at wavelengths off-resonant to its plasmon resonances. The technique relies on decoration of the tip with appropriate auxiliary molecules. For instance, a tip originally bearing a plasmon resonance at $λ_{\rm p}=581$ nm can be effectively operated off-resonantly at $λ_{\rm exc}=532$ nm, when it is decorated by an appropriate auxiliary molecule. Furthermore, the near-field is found to be strongest just below the auxiliary molecule which enables a single-molecule-size ultra-high spatial resolution imaging. We demonstrate the phenomenon with exact solutions of 3D Maxwell equations. We also show why such an enhancement takes place.

cond-mat.mes-hall↗

arXiv2019

Nonclassicality and entanglement for wavepackets

Mode-entanglement based criteria and measures become insufficient for broadband emission, e.g. from spasers (plasmonic nano-lasers). We introduce criteria and measures for the (i) total entanglement of two wavepackets, (ii) entanglement of a wavepacket with an ensemble and (iii) total nonclassicality of a wavepacket~(WP). We discuss these criteria in the context of (i) entanglement of two WPs emitted from two initially entangled cavities (or two initially entangled atoms) and (ii) entanglement of an emitted WP with the ensemble/atom for the spontaneous emission and the single-photon superradiance. We also show that, (iii) when the two constituent modes of a WP are entangled, this creates nonclassicality in the WP as a noise reduction below the standard quantum limit. The criteria we introduce are, all, compatible with near-field detectors.

quant-ph↗