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Different types of concave plasmonic nanoresonators have been optimized to achieve superradiantly enhanced emission of SiV color centers in diamond. Comparative study has been performed to consider advantages of different N number of SiV color centers, different diamond-silver (bare) and diamond-silver-diamond (coated) core-shell nanoresonator types, as well as of spherical and ellipsoidal geometry. The complete fluorescence enhancement (qualified by Px factor) monitoring and the cQE corrected quantum efficiency weighted PxcQE objective function optimization promotes to design bad-cavities for plasmonic Dicke effect. The switching into a collective Dicke state via optimized nanoresonators results in a radiated power proportional to N^2, which manifest itself in an enhancement proportional to N both of the excitation and emission rates. Accordingly, enhancement proportional to N^2 of the Px factor and PxcQE has been reached both via four and six SiV color centers arranged in symmetrical square and hexagonal patterns inside all types of inspected nanoresonators. Coated spherical and bare ellipsoidal nanoresonators result in stronger non-cooperative fluorescence enhancement, while superradiance is better achieved via bare spherical nanoresonators independently of SiV color centers number, and via coated (bare) ellipsoidal nanoresonators seeded by four (six) SiV color centers. Indistinguishable superradiant state of four color centers and line-width narrowing is achieved via bare nanoresonators. Six color centers seeded bare spherical (ellipsoidal) nanoresonators result in larger fluorescence enhancement and more significantly overridden superradiance thresholds, while having slightly more (less) pronounced bad-cavity characteristics. Both phenomena are simultaneously optimized in ellipsoidal bare nanoresonators embedding six color centers with a slightly larger detuning., Comment: 14 pages, 5 figures in paper, 8 figures and corresponding tables in Supporting information

Optical response of silicon (SiV) and nitrogen (NV) vacancy diamond color centers coupled to silver and gold nanorod dimers was numerically inspected. Optimization of the coupled emitter - nanorod dimer configurations was performed to attain the highest possible fluorescence enhancement by enhancing the excitation and emission of color centers simultaneously through plasmonic antenna resonances. To minimize losses conditional optimization was realized by setting a criterion regarding the minimum quantum efficiency of the coupled system (cQE). Restricted symmetric and allowed asymmetric antenna designs were also inspected to prove the potential advantages of asymmetric configurations tuneability. Among all inspected systems the highest 2.59*10^8 fluorescence enhancement with 46.08% cQE was achieved in case of NV color center coupled to asymmetric silver nanoantenna dimer. This is 3.17-times larger than the enhancement in corresponding symmetric configuration, which has larger 68.52% cQE. In case of SiV color center the highest 1.04*10^8 fluorescence enhancement with 37.83% cQE was achieved via asymmetric silver nanoantenna dimer. This is 1.06-times larger than the enhancement in the corresponding symmetric configuration, which has larger 57.46% cQE. The highest fluorescence enhancement achieved by gold nanorods is 4.75*10^4 with 21.8% cQE, which was shown in case of SiV color center coupled to asymmetric dimer. The attained enhancement is 8.48- (92.42-) times larger than the fluorescence enhancement achievable via symmetric (asymmetric) gold nanorod dimer coupled to SiV (NV) color center., Comment: 17 pages, 8 figures

Configuration of three different concave silver core-shell nanoresonators was numerically optimized to enhance the excitation and emission of embedded silicon vacancy (SiV) diamond color centers simultaneously. According to the tradeoff between the radiative rate enhancement and quantum efficiency (QE) conditional optimization was performed to ensure ~2-3-4 and 5-fold apparent cQE enhancement of SiV color centers with ~10% intrinsic QE. The enhancement spectra, as well as the near-field and charge distribution were inspected to uncover the physics underlying behind the optical responses. The conditionally optimized coupled systems were qualified by the product of the radiative rate enhancements at the excitation and emission, which is nominated as Px factor. The optimized spherical core-shell nanoresonator containing a centralized emitter is capable of enhancing considerably the emission via bonding dipolar resonance. The Px factor is 529-fold with 49.7% cQE at the emission. Decentralization of the emitter leads to appearance of higher order multipolar modes, which is not advantageous caused by their nonradiative nature. Transversal and longitudinal dipolar resonances of the optimized ellipsoidal core-shell resonator were tuned to the excitation and emission, respectively. The simultaneous enhancements result in 6.2x10^5 Px factor with 50.6% cQE at the emission. Rod-shaped concave core-shell nanoresonators exploit similarly transversal and longitudinal dipolar resonances, moreover they enhance the fluorescence more significantly due to their antenna-like geometry. Px factor of 8.34x10^5 enhancement is achievable while the cQE is 50.3% at the emission. The enhancement can result in 2.03x10^6-fold Px factor, when the criterion regarding the minimum QE is set to 20%., Comment: 15 pages, 10 figures

Plasmonic biosensing chips were prepared by fabricating wavelength-scaled dielectric-metal interfacial gratings on polymer film covered bimetal layers. Lysozyme biomolecules (LYZ) and gold nanoparticle bioconjugates (AuNP-LYZ) with 1:5 mass ratio were seeded onto the biochip surfaces. Comparison of the reflectance curves measured in a modified Kretschmann arrangement and computed numerically proved that monitoring the narrower secondary peaks under optimal rotated-grating coupling condition makes it possible to achieve enhanced sensitivity in biodetection. The enlarged resonance peak shift is due to the horizontally and vertically antisymmetric long-range plamonic modes propagating at the edge of the valleys and hills, which originate from Bragg scattered surface plasmon polaritons. The sensitivity is further increased in case of bioconjugates due to the coupled localized resonances on Au NPs., Comment: 20 pages, 6 figures

A novel numerical methodology has been developed, which makes possible to optimize arbitrary emitting dipole and plasmonic nano-resonator configuration with an arbitrary objective function. By selecting quantum efficiency as the objective function that has to be maximized at preselected Purcell factor criteria, optimization of plasmonic nanorod based configurations has been realized to enhance fluorescence of NV and SiV color centers in diamond. Gold and silver nanorod based configurations have been optimized to enhance excitation and emission separately, as well as both processes simultaneously, and the underlying nanophotonical phenomena have been inspected comparatively. It has been shown that considerable excitation enhancement is achieved by silver nanorods, while nanorods made of both metals are appropriate to enhance emission. More significant improvement can be achieved via silver nanorods at both wavelengths of both color centers. It has been proven that theoretical limits originating from metal dielectric properties can be approached by simultaneous optimization, which results in configurations determined by preferences corresponding to the emission. Larger emission enhancement is achieved via both metals in case of SiV center compared to the NV center. Gold and silver nanorod based configurations making possible to improve SiV centers quantum efficiency by factors of 1.18 and 5.25 are proposed, which have potential applications in quantum information processing., Comment: 20 pages, 8 figures

Dispersion characteristics of four types of superconducting nanowire single photon detectors, nano-cavity-array- (NCA-), nano-cavity-deflector-array- (NCDA-), nano-cavity-double-deflector-array- (NCDDA-) and nano-cavity-trench-array- (NCTA-) integrated (I-A-SNSPDs) devices was optimized in three periodicity intervals commensurate with half-, three-quarter- and one SPP wavelength. The optimal configurations capable of maximizing NbN absorptance correspond to periodicity dependent tilting in S-orientation (90{\deg} azimuthal orientation). In NCAI-A-SNSPDs absorptance maxima are reached at the plasmonic Brewster angle (PBA) due to light tunneling. The absorptance maximum is attained in a wide plasmonic-pass-band in NCDAI_1/2*lambda-A, inside a flat-plasmonic-pass-band in NCDAI_3/4*lambda-A and inside a narrow plasmonic-band in NCDAI_lambda-A. In NCDDAI_1/2*lambda-A bands of strongly-coupled cavity and plasmonic modes cross, in NCDDAI_3/4*lambda-A an inverted-plasmonic-band-gap develops, while in NCDDAI_lambda-A a narrow plasmonic-pass-band appears inside an inverted-minigap. The absorptance maximum is achieved in NCTAI_1/2*lambda-A inside a plasmonic-pass-band, in NCTAI_3/4*lambda-A at inverted-plasmonic-band-gap center, while in NCTAI_lambda-A inside an inverted-minigap. The highest 95.05% absorptance is attained at perpendicular incidence onto NCTAI_lambda-A. Quarter-wavelength type cavity modes contribute to the near-field enhancement around NbN segments except in NCDAI_lambda-A and NCDDAI_3/4*lambda-A. The polarization contrast is moderate in NCAI-A-SNSPDs (~10^2), NCDAI- and NCDDAI-A-SNSPDs make possible to attain considerably large polarization contrast (~10^2-10^3 and ~10^3-10^4), while NCTAI-A-SNSPDs exhibit a weak polarization selectivity (~10-10^2)., Comment: 26 pages, 8 figures