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Observation of evolution dynamics from bound states to single-pulse states in a passively mode-locked fiber laser
摘要： We report what is, to our knowledge, the first experimental observation of the ultrafast evolution dynamics from bound states (BSs) to single-pulse states (SPSs) by using the dispersive Fourier-transform (DFT) technique. The evolutions from three categories of initial BSs to SPSs are spectrally resolved in real time. Usually, accompanied by complex soliton–soliton interaction and competition, one of the two bound pulses weakens to disappearance, and the other one evolves into SPS. During the transition, the two bound pulses ordinarily depart away from each other with complex changes of relative phase. However, it is found that not all the evolutions are accompanied by the increase of temporal separation between two bound pulses. The obtained results would facilitate a deep understanding of complex dynamics in nonlinear systems and provide valuable data for further theoretical studies.
关键词： single-pulse states,bound states,fiber lasers,Ultrafast evolution dynamics
更新于2025-11-28 14:24:03
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Experimental Observation of Bound States of 2D Dirac Electrons at Surface Steps of the Topological Insulator Bi <sub/>2</sub> Se <sub/>3</sub>
摘要： Topologically protected surface states of three-dimensional topological insulators provide a model framework for studying massless Dirac electrons in two dimensions. Usually a step on the surface of a topological insulator is treated as a scatterer for the Dirac electrons, and the study of its effect is focused on the interference of the incident and scattered electrons. Then a major role plays the warping of the Dirac cone far from the Dirac point. The existence of another significant effect near the Dirac point brought about by the presence of steps is experimentally demonstrated here. Namely the band bending in the vicinity of steps leads to formation of 1D bound states in the corresponding potential wells. The observation of bound states in such potential wells in our scanning tunneling microscopy and spectroscopy investigation of the surface of the topological insulator Bi2Se3 is reported. Numerical simulations support our conclusion and provide a recipe for the identification of such states.
关键词： density of states,Dirac electrons,surface states,edge states,bound states,scanning tunneling microscopy,Bi2Se3,topological insulators,scanning tunneling spectroscopy
更新于2025-09-23 15:23:52
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Avoided crossings and bound states in the continuum in low-contrast dielectric gratings
摘要： We consider bound states in the continuum (BICs) in low-contrast dielectric gratings. It is demonstrated that the BICs originate from the reduced guided modes on the effective dielectric slab with the permittivity equal to the average permittivity of the dielectric grating. In the case of isolated resonances, the positions of BICs can be found from two-wave dispersion relationships for guided leaky modes. In the case of the degeneracy between the two families of leaky modes, the system exhibits an avoided crossing of resonances. In the spectral vicinity of the avoided crossing the transmittance as well as the emergence of BICs is described in the framework of the generic formalism by Volya and Zelevinsky [Phys. Rev. C 67, 054322 (2003)] with a single fitting parameter.
关键词： leaky modes,dielectric gratings,bound states in the continuum,avoided crossings
更新于2025-09-23 15:21:21
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Nondegeneracy and stability of antiperiodic bound states for fractional nonlinear Schr?dinger equations
摘要： We consider the existence and stability of real-valued, spatially antiperiodic standing wave solutions to a family of nonlinear Schr?dinger equations with fractional dispersion and power-law nonlinearity. As a key technical result, we demonstrate that the associated linearized operator is nondegenerate when restricted to antiperiodic perturbations, i.e. that its kernel is generated by the translational and gauge symmetries of the governing evolution equation. In the process, we provide a characterization of the antiperiodic ground state eigenfunctions for linear fractional Schr?dinger operators on R with real-valued, periodic potentials as well as a Sturm–Liouville type oscillation theory for the higher antiperiodic eigenfunctions.
关键词： antiperiodic bound states,nondegeneracy,fractional nonlinear Schr?dinger equations,stability
更新于2025-09-23 15:21:21
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Extreme Huygens' metasurfaces based on quasi-bound states in the continuum
摘要： We introduce the concept and a generic approach to realize Extreme Huygens’ Metasurfaces by bridging the concepts of Huygens’ conditions and optical bound states in the continuum. This novel paradigm allows creating Huygens’ metasurfaces whose quality factors can be tuned over orders of magnitudes, generating extremely dispersive phase modulation. We validate this concept with a proof-of-concept experiment at the near-infrared wavelengths, demonstrating all-dielectric Huygens’ metasurfaces with different quality factors. Our study points out a practical route for controlling the radiative decay rate while maintaining the Huygens’ condition, complementing existing Huygens’ metasurfaces whose bandwidths are relatively broad and complicated to tune. This novel feature can provide new insight for various applications, including optical sensing, dispersion engineering and pulse-shaping, tunable metasurfaces, meta-devices with high spectral selectivity, and nonlinear meta-optics.
关键词： all-dielectric,dispersion,bound states in the continuum,Huygens’ condition,metasurfaces
更新于2025-09-23 15:21:21
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Hybrid atom-molecule quantum walks in a one-dimensional optical lattice
摘要： We study hybrid atom-molecule quantum walks in one-dimensional optical lattices with two interacting bosonic atoms which may be converted into a molecule. The hybrid atom-molecule energy bands include a continuum band and two isolated bands, which respectively correspond to scattering states and dressed bound states (DBSs). Because of the atom-molecule coupling, the DBSs may appear even in the absence of atom-atom interaction. From an initial state of two atoms occupying the same site, in addition to independent quantum walks which correspond to scattering states, correlated quantum walks appear as a signature of DBSs. Even if the atom-atom interaction and the atom-molecule coupling are much stronger than the tunneling strengths, independent quantum walks may still appear under certain resonant conditions. The correlated quantum walks show two light cones with different propagation velocities, which can be analytically explained by the effective tunneling strengths of the two different DBSs. Furthermore, the effective nearest-neighbor tunneling of DBSs can be suppressed to zero, which can be explained by the destructive interference between the atomic pair and the molecule.
关键词： Quantum walks,dressed bound states,atom-molecule coupling,tunneling,optical lattices
更新于2025-09-23 15:21:01
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Aharonov-Bohm Interferometer in a T-Shaped Quantum Dot Embedded in Majorana Bound States
摘要： We theoretically study the spin-dependent transport properties of an Aharonov-Bohm (AB) interferometer composed by a T-shaped quantum dot (QD) embedded in Majorana bound states (MBS). We use the equation of motion method to calculate the conductance across the interferometer. We note that the conductance exhibits sensitive dependence on the MBS-QD coupling strength as well as the polarization strength of the leads when the phase factor of AB ring changes periodically. The conductance shows a transition from resonance to anti-resonance when the MBS-QD coupling strength changes from small to large. Also, there is di?erent p-dependence conductance when the leads alignment changes from parallel to anti-parallel. These ?ndings suggest that such a model could be used for a sensitive detection of MBS interactions, exploiting the high sensitivity of conductance to the AB phase in the interferometer.
关键词： quantum dot,Majorana bound states,Aharonov-Bohm e?ect
更新于2025-09-23 15:19:57
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Fanoa??Andreev and Fanoa??Majorana Correspondence in Quantum Dot Hybrid Structures
摘要： A correspondence on the single-electron transport properties between systems of different nature, a topological quantum system and a (conventional) non-topological one, is demonstrated. Specifically, the equivalence between the Fano resonances obtained in T-shaped double quantum dot system coupled to a superconducting lead (QD–QD–S) and a topological superconductor ring nanowire (QD–MBSs) is presented. The non-zero value of the Fano (anti)resonance in the conductance of the QD-MBSs systems is shown as a consequence of a complex Fano factor qM, which is equivalent to the complex Fano factor qS of the QD–QD–S. The complex nature of qS is understood as a sign of a phase introduced by the superconducting lead in the QD–QD–S. It is because of this phase that the correspondence between the QD–QD–S and the QD–MBSs is possible. It is believed that these results can help to reveal the importance of the Fano interference process toward the understanding of the role of the superconductor lead in the QD–QD–S system as well as giving a clear signature of the presence of MBS’s in the topological system.
关键词： Majorana bound states,proximity effects,Andreev reflection,(anti)fano resonances,topological superconductors
更新于2025-09-23 15:19:57
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Experimental observation of bound states of Q-switched fiber lasers mode-locked by carbon nanotubes
摘要： We demonstrate the experimental observation of bound states of Q-switched lasers mode-locked by carbon nanotubes. When bound states of Q-switched mode-locked lasers are formed, the Fourier transformation results into multiwavelength spectrum due to the small temporal interval induced by polarization controller. We find that the wavelength spacing is highly sensitive to pump power. A wavelength spacing tuning from ~0.057 nm to 1.569 nm with a pump power variation less than 4 mW is obtained. The wavelength spacing is also highly sensitive to the nonlinear phase induced by polarization controller. These findings enrich our understanding about the complex dynamics of the Q-switched mode-locked lasers.
关键词： carbon nanotubes,bound states,mode-locked,nonlinear phase,Q-switched fiber lasers
更新于2025-09-23 15:19:57
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Guided‐Mode Resonances in All‐Dielectric Terahertz Metasurfaces
摘要： Coupling of diffracted waves in gratings with the waveguide modes gives rise to the guided mode resonances (GMRs). The GMRs provide designer linewidth and resonance intensity amidst a broad background, and thus have been widely used for numerous applications in visible and infrared spectral regions. Here, terahertz GMRs are demonstrated in low-loss, all-dielectric metasurfaces, which are periodic square lattices of silicon cuboids on quartz substrates. The silicon cuboid lattice simultaneously acts as a diffraction grating and an in-plane slab waveguide, thereby resulting in the formation of terahertz GMRs. At oblique incidence, two distinct frequency detuned GMRs are observed. The frequency difference between these two GMRs increases at larger angle of incidence. However, extremely small angle of incidence causes destructive interference between these counter-propagating GMRs that leads to a nonradiative symmetry-protected bound state in the continuum. GMRs in all-dielectric silicon metasurfaces can have potential applications in the realization of efficient terahertz devices such as high-Q transmission filters with angular spectral selectivity, ultrafast modulators, and free-space couplers.
关键词： guided-mode resonance,bound states in the continuum,all-dielectric metasurface,terahertz
更新于2025-09-19 17:13:59