arXiv subjects

Ying Gu

Publications and source records attributed to Ying Gu.

46 records · Page 3Linked to original sources

arXiv2021

Local phase delay effect on the asymmetric spectroscopy of plasmon-exciton coupling systems

The phase delay of a local electric field, being well-known in plasmonic nanostructures, has seldom been investigated to modulate the plasmon-exciton interaction. Here, with the single-particle spectroscopy method, we experimentally investigate the phase effect in plasmon-exciton coupling systems consisting of monolayer WSe2 and an individual gold nanorod. The local plasmon phase delay is tuned by adopting various nanorods with different resonant energies respective to the exciton. We find that the local plasmon phase delay between the excitons and the plasmonic modes is as equally essential as the amplitude. The phase delay modulates the plasmon-exciton coupling considerably, resulting in an asymmetric spectral line-shape due to the interference behavior. There is an excellent agreement for the phase delay between the numerically calculated near-field phase distribution and the experimental results. The local phase delay can act as an effective way to modulate the properties of plexcitonic coupling at the nanoscale, which may have potential applications in nanoscale sensing, solar energy devices, and enhancing nonlinear processes.

physics.optics↗

arXiv2020

Nesting and Degeneracy of Mie Resonances of Dielectric Cavities within Zero-Index Materials

Resonances in optical cavities have been used to manipulate light propagation, enhance light-matter interaction, modulate quantum states, and so on. However, in traditional cavities, the permittivity contrast in and out the cavity is not so high. Recently, zero-index materials (ZIMs) with unique properties and specific applications have attracted great interest. By putting optical cavity into ZIMs, the extreme circumstance with infinite permittivity contrast can be obtained. Here, we theoretically study Mie resonances of dielectric cavities embedded in ZIMs with $\varepsilon \approx 0$, or $μ\approx 0$, or $(\varepsilon,μ) \approx 0$. Owing to ultrahigh contrast ratio of $\varepsilon$ or $μ$ in and out the cavities, with fixed wavelength, a series of Mie resonances with the same angular mode number $l$ but with different cavity radii are obtained; more interestingly, its $2^l$-TM (TE) and $2^{l+1}$-TE (TM) modes have the same resonant solution for the cavity in $\varepsilon \approx 0$ ($μ\approx 0$) material, and the resonance degeneracy also occurs between $2^l$-TM mode and $2^l$-TE mode for $(\varepsilon,μ) \approx 0$ material. We further use resonance degeneracy to modulate the Purcell effect of quantum emitter inside the cavity. The results of resonance nesting and degeneracy will provide an additional view or freedom to enhance the performance of cavity behaviors.

physics.optics↗

arXiv2019

Topologically Enabled Ultralarge Purcell Enhancement Robust to Photon Scattering

Micro/nanoscale single photon source is a building block of on-chip quantum information devices. Owing to possessing ultrasmall optical mode volume, plasmon structures can provide large Purcell enhancement, however scattering and absorption are two barriers to prevent them from being used in practice. To overcome these barriers, we propose the topological photonic structure containing resonant plasmon nanoantenna, where nanoantenna provides large Purcell enhancement while topological photonic crystal guides all scattering light into its edge state. Through the optical mode design, the rate of single photons emitted into the edge state reaches more than 104γ0 simultaneously accompanied with an obvious reduction of absorption. This kind of nonscattering large Purcell enhancement will provide new sight for on-chip quantum light sources such as a single photon source and nanolaser.

physics.optics↗

arXiv2019

SNR-adaptive OCT angiography enabled by statistical characterization of intensity and decorrelation with multi-variate time series model

In OCT angiography (OCTA), decorrelation computation has been widely used as a local motion index to identify dynamic flow from static tissues, but its dependence on SNR severely degrades the vascular visibility, particularly in low- SNR regions. To mathematically characterize the decorrelation-SNR dependence of OCT signals, we developed a multi-variate time series (MVTS) model. Based on the model, we derived a universal asymptotic linear relation of decorrelation to inverse SNR (iSNR), with the variance in static and noise regions determined by the average kernel size. Accordingly, with the population distribution of static and noise voxels being explicitly calculated in the iSNR and decorrelation (ID) space, a linear classifier is developed by removing static and noise voxels at all SNR, to generate a SNR-adaptive OCTA, termed as ID-OCTA. Then, flow phantom and human skin experiments were performed to validate the proposed ID-OCTA. Both qualitative and quantitative assessments demonstrated that ID-OCTA offers a superior visibility of blood vessels, particularly in the deep layer. Finally, implications of this work on both system design and hemodynamic quantification are further discussed.

physics.med-ph↗

arXiv2018

A photonic interface of chiral cavity quantum electrodynamics

Cavity quantum electrodynamics studies light-matter interactions at single quanta level. Chiral photon-emitter coupling in photonic structures is characterized as unidirectional propagation locked by the local polarization of light. However, to realize the strong interaction of photon-emitter with direction-locked propagation, which will bring novel applications in nonreciprocal quantum devices, has not been reported yet. Here, we propose the coupled photonic crystal and metallic nanoparticle structure, where through strong local field with high helicity, the rate of circularly polarized photons emitting into photonic crystal waveguide is one order larger than that without the nanoparticle and the linewidth of Rabi splitting spectra is about one-tenth of that with only the nanoparticle, both with $\sim$ 95$\%$ photons propagating unidirectionally, which can be utilized in directional quantum light sources.

physics.optics↗

arXiv2009

Quantum-information transfer in a coupled resonator waveguide

We propose an efficient scheme for the implementation of quantum information transfer in a onedimensional coupled resonator waveguide. We show that, based on the effective long-range dipole-dipole interactions between the atoms mediated by the cavity modes, Raman transitions between the atoms trapped in different nodes can take place. Quantum information could be transferred directly between the opposite ends of the coupled waveguide without involving the intermediate nodes via either Raman transitions or the stimulated Raman adiabatic passages. Since this scheme, in principle, is a one-step protocol, it may provide useful applications in quantum communications.

quant-ph↗

arXiv2007

Deterministic generation of polarization-entangled photon pairs in a cavity-QED system

We propose a cavity-QED scheme that can deterministically generate Einstein-Podosky-Rosen polarization-entangled photon pairs. A four-level tripod atom successively couples to two high-Q optical cavities possessing polarization degeneracy, assisted by a classical $π$-polarized pump field. The stimulated Raman adiabatic passage process in the atom-cavity system is used to produce the polarization-entangled photon pairs. The proposal is particularly robust against atomic spontaneous decay, which should have potential applications in quantum information processing.

quant-ph↗

arXiv2002

Quantum coherence in a degenerate two-level atomic ensemble: for a transition $F_e=0\leftrightarrow F_g=1$

For a transition $F_e=0\leftrightarrow F_g=1$ driven by a linearly polarized light and probed by a circularly light, quantum coherence effects are investigated. Due to the coherence between the drive Rabi frequency and Zeeman splitting, electromagnetically induced transparency, electromagnetically induced absorption, and the transition from positive to negative dispersion are obtained, as well as the populations coherently oscillating in a wide spectral region. At the zero pump-probe detuning, the subluminal and superluminal light propagation is predicted. Finally, coherent population trapping states are not highly sensitive to the refraction and absorption in such ensemble.

quant-ph↗

arXiv2002

Fluctuations and scaling of inverse participation ratios in random binary resonant composites

We study the statistics of local field distribution solved by the Green's-function formalism (GFF) [Y. Gu et al., Phys. Rev. B {\bf 59} 12847 (1999)] in the disordered binary resonant composites. For a percolating network, the inverse participation ratios (IPR) with $q=2$ are illustrated, as well as the typical local field distributions of localized and extended states. Numerical calculations indicate that for a definite fraction $p $ the distribution function of IPR $P_q$ has a scale invariant form. It is also shown the scaling behavior of the ensemble averaged $ $ described by the fractal dimension $D_q$. To relate the eigenvectors correlations to resonance level statistics, the axial symmetry between $D_2$ and the spectral compressibility $χ$ is obtained.

cond-mat.soft↗

arXiv2001

Local-field distribution in resonant composites: Green's-function formalism

The effective response depends sensitively on composite microstructure due to large fluctuations in the local electric field. For metallic clusters embedded in a dielectric host, the local field distributions are extremely inhomogeneous in space around the metallic clusters due to quasi-static resonance, leading to a large enhancement in the effective linear and nonlinear responses. In this work, we propose a general method for computing the electric field of metallic clusters near resonance via a perturbation formalism. We illustrate the method by simple examples.

cond-mat.soft↗