Fano-like Interference Research Articles

Exciton–photocarrier interference in mixed lead-halide-perovskite nanocrystals

The use of semiconductor nanocrystals in scalable quantum technologies requires characterization of the exciton coherence dynamics in an ensemble of electronically isolated crystals in which system–bath interactions are nevertheless strong. In this communication, we identify signatures of Fano-like interference between excitons and photocarriers in the coherent two-dimensional photoluminescence excitation spectral lineshapes of mixed lead-halide perovskite nanocrystals in dilute solution. Specifically, by tuning the femtosecond-pulse spectrum, we show such interference in an intermediate coupling regime, which is evident in the coherent lineshape when simultaneously exciting the exciton and the free-carrier band at higher energy. We conclude that this interference is an intrinsic effect that will be consequential in the quantum dynamics of the system and will thus dictate decoherence dynamics, with consequences in their application in quantum technologies.

Exciton-carrier coupling in a metal halide perovskite nanocrystal assembly probed by two-dimensional coherent spectroscopy

The surface chemistry and inter-connectivity within perovskite nanocrystals play a critical role in determining the electronic interactions. They manifest in the Coulomb screening of electron–hole correlations and the carrier relaxation dynamics, among other many-body processes. Here, we characterize the coupling between the exciton and free carrier states close to the band-edge in a ligand-free formamidinium lead bromide nanocrystal assembly via two-dimensional coherent spectroscopy. The optical signatures observed in this work show: (i) a nonlinear spectral lineshape reminiscent of Fano-like interference that evidences the coupling between discrete electronic states and a continuum, (ii) symmetric excited state absorption cross-peaks that suggest the existence of a coupled exciton-carrier excited state, and (iii) ultrafast carrier thermalization and exciton formation. Our results highlight the presence of coherent coupling between exciton and free carriers, particularly in the sub-100 femtosecond timescales.

Controlling periodic Fano resonances of quantum acoustic waves with a giant atom coupled to a microwave waveguide

Nanoscale Fano resonances, with applications from telecommunications to ultra-sensitive biosensing, have prompted extensive research. We demonstrate that a superconducting qubit, jointly coupled to microwave waveguides and an inter-digital transducer composite device, can exhibit acoustic Fano resonances. Our analytical framework, leveraging the Taylor series approximation, elucidates the origins of these quantum acoustic resonances with periodic Fano-like interference. By analyzing the analytical Fano parameter, we demonstrate that the Fano resonances and their corresponding Fano widths near the resonance frequency of a giant atom can be precisely controlled and manipulated by adjusting the time delay. Moreover, not just the near-resonant Fano profiles, but the entire periodic Fano resonance features can be precisely modulated from Lorentz, Fano to quasi-Lorentz shapes by tuning the coupling strength of the microwave waveguide. Our analytical framework offers insights into the control and manipulation of periodic Fano resonances in quantum acoustic waves, thereby presenting significant potential for applications such as quantum information processing, sensing, and communication.

Magnetic field effect on transport properties of double quantum dot — Majorana wire system in cross-shaped configuration

We theoretically study the influence of an external magnetic field on the transport properties of a double quantum dot (DQD)-Majorana nanowire system in a cross-shaped configuration with central dot coupled to a superconductor and normal metallic leads. In such a system, we can observe a subtle interplay between generation of Andreev bound states, Majorana mode leaking into quantum dots and interdots Fano-like interference processes. We show that properly selected side-coupled quantum dot energy can slow down/activate the process of Majorana mode leaking into DQD and additionally can strongly affect the differential and linear conductance in the considered system. We also study the influence of spin polarization of quantum dot–Majorana mode coupling on the transport properties of the considered system, especially on its linear conductance.

Study on Sound-Insulation Performance of an Acoustic Metamaterial of Air-Permeable Multiple-Parallel-Connection Folding Chambers by Acoustic Finite Element Simulation.

In order to achieve a balance between sound insulation and ventilation, a novel acoustic metamaterial of air-permeable multiple-parallel-connection folding chambers was proposed in this study that was based on Fano-like interference, and its sound-insulation performance was investigated through acoustic finite element simulation. Each layer of the multiple-parallel-connection folding chambers consisted of a square front panel with many apertures and a corresponding chamber with many cavities, which were able to extend both in the thickness direction and in the plane direction. Parametric analysis was conducted for the number of layers nl and turns nt, the thickness of each layer L2, the inner side lengths of the helical chamber a1, and the interval s among the various cavities. With the parameters of nl = 10, nt = 1, L2 = 10 mm, a1 = 28 mm, and s = 1 mm, there were 21 sound-transmission-loss peaks in the frequency range 200-1600 Hz, and the sound-transmission loss reached 26.05 dB, 26.85 dB, 27.03 dB, and 33.6 dB at the low frequencies 468 Hz, 525 Hz, 560 Hz, and 580 Hz, respectively. Meanwhile, the corresponding open area for air passage reached 55.18%, which yielded a capacity for both efficient ventilation and high selective-sound-insulation performance.

Quench dynamics of Fano-like resonances in the presence of the on-dot superconducting pairing

We explore the electron dynamics of a system composed of double quantum dot embedded between metallic and superconducting leads in a “T-shape” geometry. In nanoscopic systems, where electron transfer between electrodes can be realized via different paths, interference effects play an important role. For double quantum dot system in the chosen geometry, interference of electrons transferred between electrodes via the interfacial quantum dot and electrons scattered on the side dot gives rise to Fano-like interference. If such a system is additionally coupled to a superconducting electrode, together with the well-understood Fano resonance an additional resonance appears on the opposite side of the Fermi level. In the recent work (Barański et al. in Sci Rep 10:2881, 2020), we showed that this resonance occurs solely as a result of the local pairing of non-scattered electrons with scattered ones. In this work, considering the quench dynamics, we explore how much time is required for formation of each of these resonances. In particular, (i) we analyze the charge oscillations between subsystems; (ii) we estimate the time required for each resonance to achieve stable equilibrium upon an abrupt change of interdot connection; (iii) we discuss a typical energy and time scales for experiments on similar architectures.

Dynamic control of Fano-like interference in the graphene periodic structure

We propose and investigate a graphene periodic subsurface structure consisting of a coplanar pair of graphene ring resonators and a graphene ribbon. The Fano-like interference can be actively regulated by the applied magnetic field, incident angle and Fermi energy. Since the excited charges of graphene monolayer have cyclotron properties in the external magnetic field, the transmittance and line-shape can be effectively controlled. At a certain frequency, different magnetic fields have different effects on the conductivity tensor of graphene, which affects the metallic properties of graphene, leading to changes in the transmittance. The Fano-like line-shape can be regulated by adjusting the incident angle to delay the phase between adjacent graphene sheets. In addition, the resonance frequency can be electrically regulated through Fermi energy. Finite element method is introduced to analyze the graphene periodic structure and the results are demonstrated by multimode interference coupled mode theory. The Faraday rotation angle exceeding 85° are observed in a small magnetic flux density B of about 0.5 T. Moreover, a plasma-optic switching with high ON/OFF ratio and large modulation depth (MD) is designed, whose ON/OFF ratio (η) and MD are 19.921 dB and 98.982%, respectively. Notably, combining the influence of magnetic flux density on transmittance and the modulation of resonance frequency by Fermi energy, optical switching can be implemented at any frequency within the frequency range studied. These results provide methods for active regulation of electromagnetic waves in the terahertz field and have potential applications in optical switching and integrated photonic circuit.

Fano-Like Resonance of Heat-Reconfigurable Silicon Grating Metasurface Tuned by Laser-Induced Graphene.

We propose a heat-reconfigurable metasurface composed of the silicon-based gold grating. The asymmetric Fano-like line shape is formed due to the mutual coupling of the local surface plasmon (LSP) in the gap between the two layers of Au gratings and the surface propagating plasmon (SPP) on the surface of the Au gratings. Then, we effectively regulate the Fano resonance by applying a bias voltage to laser-induced graphene (LIG), to generate Joule heat, so that the resonant dip of one mode of the Fano resonance can shift up to 28.5 nm. In contrast, the resonant dip of the other mode barely changes. This effectively regulates the coupling between two resonant modes in Fano resonance. Our study presents a simple and efficient method for regulating Fano-like interference in the near-infrared band.

Ventilation barrier with space-coiling channels of varying cross-section for broadband sound insulation

Efficient broadband silencing of low-frequency sound (<1000 Hz) while retaining the fluid free-flow remains a challenge in acoustical engineering. Here, a ventilated acoustic barrier, consisting of an unrestricted channel and a space-coiling structure with variable cross-sections, is proposed based on Fano-like interference. With the design of the proposed binary structure, the incident sound energy can be effectively attenuated by 90 % in the range of 377 Hz to 425 Hz and 454 Hz to 518 Hz, even at a relatively large opening rate (airflow rate >73 %). Furthermore, the susceptibility of the bands to geometrical parameters and incidence angles is investigated. The structure parameters are optimized using a genetic algorithm to achieve sound attenuation in a broader band from 400 Hz to 1000 Hz. It is shown that this design demonstrates excellent viability for customizing broadband and processing sound from various directions. Experiments are performed to verify the proposed design, and the results are in agreement with the numerical calculations and theoretical predictions. The developed barrier might be potentially applicable to scenarios desiring for low-frequency noise mitigation and free airflow.

Quasinormal modes of spheroidal resonators in the null-field framework and application to hybrid anapoles

A model for calculating the quasinormal modes (QNMs) of homogeneous and core-shell spheroidal resonators is formulated in the null-field framework. Relying on a multipole expansion of the electromagnetic fields, the Mittag-Leffler theorem is employed to extract the QNMs from the poles of a response matrix. Physical quantities such as the extinction and scattering efficiency and the total internal energy of a mode are expressed directly in terms of the multipole expansion coefficients. We apply the model to study hybrid anapoles, which are radiationless states characterized by an enhancement of the total internal energy. Interference between excited QNMs and the background comprising of all other QNMs leads to a suppression of the extinction efficiency. Further, we show this suppression is due to Fano-like interference between resonant and background multipoles.

Directional Plasmonic Excitation by Helical Nanotips.

The phenomenon of coupling between light and surface plasmon polaritons requires specific momentum matching conditions. In the case of a single scattering object on a metallic surface, such as a nanoparticle or a nanohole, the coupling between a broadband effect, i.e., scattering, and a discrete one, such as surface plasmon excitation, leads to Fano-like resonance lineshapes. The necessary phase matching requirements can be used to engineer the light–plasmon coupling and to achieve a directional plasmonic excitation. Here, we investigate this effect by using a chiral nanotip to excite surface plasmons with a strong spin-dependent azimuthal variation. This effect can be described by a Fano-like interference with a complex coupling factor that can be modified thanks to a symmetry breaking of the nanostructure.

Broadband ventilated metamaterial silencer for high reflection based on Fano-like interference

Conventional sound shielding structures is difficult to meet the requirements of low-to-middle frequency broadband sound insulation and free ventilation. In this paper, we propose a ventilated metamaterial silencer based on Fano-like interference, which can achieve the sound transmission loss (STL) of more than 10 dB in the range of 516–970 Hz with subwavelength thickness (0.11 [Formula: see text]) while remains an opening area ratio of 23%. The designed silencer is composed of a large central orifice and four surrounding coiling channels, making the sound waves passing through the two areas generate Fano-like asymmetric transmission spectrum and form efficient reflection to insulate sound coming from various directions. The parametric studies are also carried out to investigate the tunable acoustic performance. Experiment measurement matches well with the simulation results. In the future, the proposed silencer may have potential applications in practical environments requiring broadband sound insulation and free air flows.

Ultrabroadband Acoustic Ventilation Barriers via Hybrid-Functional Metasurfaces

Ventilation barriers allowing simultaneous sound blocking and free airflow passage are of great challenge but necessary for particular scenarios calling for sound-proofing ventilation. Previous works based on local resonance or Fano-like interference serve a narrow working range around the resonant or destructive-interference frequency. Efforts made on broadband designs show a limited bandwidth typically smaller than half an octave. Here, we theoretically design an ultra-broadband ventilation barrier via hybridizing dissipation and interference. Confirmed by experiments, the synergistic effect from our hybrid-functional metasurface significantly expand the scope of its working frequencies, leading to an effective blocking of more than 90% of incident energy in the range of 650-2000 Hz, while its structural thickness is only 53 mm $(\sim \lambda / 10)$. Our design shows great flexibility in customizing the broadband and is capable of handling sound coming from various directions, which has potential in air-permeable yet sound-proofing applications.

Bi2Se3-Functionalized Metasurfaces for Ultrafast All-Optical Switching and Efficient Modulation of Terahertz Waves

Because of the wealth of fascinating physical phenomena observed in topological insulators (TIs), their exciting properties have been intensively investigated for electronic and optoelectronic applications, such as quantum devices, saturable absorbers, and photodetectors, in the visible to terahertz (THz) spectral range. However, their potential for metaphotonic devices has yet to be explored. Here, we present a comprehensive investigation on the active photonic performance of a novel metaphotonic device by hybridizing ultrathin Bi2Se3 bridges into metamaterials in the THz range. Unlike THz modulation via Fano-like plasmon-phonon destructive interference in the pure Bi2Se3 structure, our Bi2Se3 microribbon arrays with high photoconductivity can short-circuit the circulating surface currents in the proposed metasurfaces, leading to remarkable electromagnetically induced transparency (EIT) transmission and group delay modulations at the operational frequency. Additionally, the width of the Bi2Se3 bridges is optimized to 20 μm to maximize the modulation depth, with the modulation of the transmission resonance amplitude and the group delay as high as 31% and 2.7 ps, respectively. Due to the short photocarrier lifetime in Bi2Se3 films (within a few picoseconds), the full recovery time after photoinjection is less than 9.5 ps, enabling an ultrafast switching speed up to a hundred GHz. The ultrafast and effective control of the light spectrum in Bi2Se3-functionalized metaphotonic systems lays the foundation for promoting the emergence of TI-based optoelectronics.

Effective Control of Photon Statistics from Electroluminescence by Fano-like Interference Effect.

The photon blockade induced by optical nonlinearity has been widely used to generate single-photon emission under optical driving in quantum optics. However, the same approach is difficult to achieve in electrically driven molecular junctions. Here we propose a scheme for tuning photon statistics via Fano-like interference effect in a system consisting of two molecules within one optical cavity. Under electrical pumping, a transition from photon bunching to antibunching takes place as a manifestation of the Fano-like interference. This effect persists even in the presence of the dipole-dipole interaction between molecules based on the parameters extracted from the experiments. Our proposal can be realized in current-carrying scanning tunneling microscope junctions.

Spectroscopic fingerprint of charge order melting driven by quantum fluctuations in a cuprate

Copper oxide high-TC superconductors possess a number of exotic orders that coexist with or are proximal to superconductivity. Quantum fluctuations associated with these orders may account for the unusual characteristics of the normal state, and possibly affect the superconductivity1–4. Yet, spectroscopic evidence for such quantum fluctuations remains elusive. Here, we use resonant inelastic X-ray scattering to reveal spectroscopic evidence of fluctuations associated with a charge order5–14 in nearly optimally doped Bi2Sr2CaCu2O8+δ. In the superconducting state, while the quasielastic charge order signal decreases with temperature, the interplay between charge order fluctuations and bond-stretching phonons in the form of a Fano-like interference increases, an observation that is incompatible with expectations for competing orders. Invoking general principles, we argue that this behaviour reflects the properties of a dissipative system near an order–disorder quantum critical point, where the dissipation varies with the opening of the pseudogap and superconducting gap at low temperatures, leading to the proliferation of quantum critical fluctuations, which melt charge order. X-ray scattering experiments show that the quantum fluctuations associated with charge order take a form that is incompatible with the idea of competition between charge order and superconductivity.

Fano-like interference induced modification of Autler-Townes doublet spectrum via phase-dependent superposition of atomic states

A four-level atomic model is proposed to exhibit the evolution of Fano-like interference effect in the spontaneous emission spectrum of Autler-Townes (AT) doublet when the atom is initially prepared in the phase-dependent superposition of quantum states. By using this model, phase-dependent generation of a narrow spectral line within the AT-doublet is predicted. This feature is shown to be modified by the AT-peak-splitting effect. In addition, it has been also shown that the latter may be accompanied by an anomalous peak shifting effect, which is found to be obtained in a typical phase-coherent atomic ensemble or phaseonium under consideration. As a whole, the emission spectrum can be obtained with three peaks instead of two peaks associated with a sharp spectral hole as a consequence of the emergence of asymmetric Fano-like resonance. This is the most interesting outcome of the present study.

Broadband Acoustic Ventilation Barriers

Conventional sound barriers impede airflow at the same time. Recent advances in acoustic metasurfaces provide a solution for air-permeable barriers utilizing the Fano-like interference. While the mechanism of Fano-like interference implies that such a realized device serves a narrow working frequency range around every destructive-interference frequency. Considering the fact that noise usually covers a wide frequency range, designing a broadband acoustic barrier is still a challenge. Here, we theoretically design a planar-profile and subwavelength-thickness (approximately $\ensuremath{\lambda}/8$) acoustic ventilation barrier prohibitive for sound in a broad range. Our design is a metasurface consisting of a central hollow orifice and two surrounding helical pathways with varying pitch. Thanks to the hornlike helical pathways, the response strength from the monopolar and dipolar modes of the system almost keeps balance in the frequency range of interest, leading to an effective blocking of more than $90\mathrm{%}$ of incident energy in the range of 900--1418 Hz. Experiments are conducted to validate the proposed design, whose results are consistent with the analytical predictions and simulations. The underlying working mechanism ensures the metasurface is capable of handling broadband sound coming from various directions. Our design has potential in air-permeable yet sound-proofing applications, such as simultaneously natural ventilation and noise reduction in green buildings.

Spectral Control of an X-Ray L-Edge Transition via a Thin-Film Cavity.

By embedding a thin layer of tantalum in an x-ray cavity, we observe a change in the spectral characteristics of an inner-shell transition of the metal. The interaction between the cavity mode vacuum and the L_{III}-edge transition is enhanced, permitting the observation of the collective Lamb shift, superradiance, and a Fano-like cavity-resonance interference effect. This experiment demonstrates the feasibility of cavity quantum electrodynamics with electronic resonances in the x-ray range with applications to manipulating and probing the electronic structure of condensed matter with high-resolution x-ray spectroscopy in an x-ray cavity setting.

Ultra-open acoustic metamaterial silencer

Recently, with advances in acoustic metamaterial science, the possibility of sound attenuation using subwavelength structures, while maintaining permeability to air, has been demonstrated. However, the ongoing challenge addressed herein is the fact that among such air-permeable structures to date, the open areas represents only small fraction of the overall area of the material. In the presented work, in order to address this challenge, we firstly demonstrate that a transversely-placed bilayer medium with large degrees of contrast in the layers' acoustic properties exhibits an asymmetric transmission, similar to the Fano-like interference phenomenon. Next, we utilize this design methodology and propose a deep-subwavelength acoustic metasurface unit cell comprising nearly 60% open area for air passage, while serving as a high-performance selective sound silencer. Finally, the proposed unit cell performance is validated experimentally, demonstrating a reduction in the transmitted acoustic energy of up to 94%. This ultra-open metamaterial (UOM) design, leveraging a Fano-like interference, enables high-performance sound silencing in a design featuring a large degree of open area, which may find utility in applications in which highly efficient, air-permeable sound silencers are required, such as smart sound barriers, fan or engine noise reduction, among others.