Objective.We investigated the competition mechanism between topological order and quasiperiodic disorder in one-dimensional double chain systems.Under the uniform limit,the Hamiltonian of the system maintains chiral symmetry,and the topological phase of the system is related to the band gap,which can be characterized by the winding number.We focus on study-ing the competition and localization transition mechanisms between topological order and quasiperiodic disorder. Methods.With numerical analysis methods,we study the energy spectrum,edge states,topological evolution,and localization properties of the system.For example,we identify topological phase transitions and edge state features from the energy spectrum,and calculate the number of windings to characterize the topological phase.Meanwhile,the phase diagram is determined by cal-culating the mean inverse participation ratio(IPR)and the mean normalized participation ratio(NPR)to distinguish the extended,localized,and critical states of the system.In addition,finite size scaling analysis is conducted to verify reentrant behavior. Results and Discussions.Our research results indicate that there is an intermediate regime in the system,where the extended state and localized state coexist,providing evidence for the emergence of a mobility edge.When this intermediate phase reappears under strong quasiperiodic modulation,it indicates the existence of nonmonotonic reentrant localization phenomenon.In addi-tion,through finite size scaling analysis,it was confirmed that this behavior is an inherent property of the system,rather than a finite size artifact.Therefore,the findings show that the competition between topological protection and disorder induced localiza-tion has generated rich phase structures. Conclusions.This work discusses the competitive physical mechanism between topological order and quasiperiodic disorder in one-dimensional double chain systems,and finds that through their interactions,mobility edges and reentrant local behavior can be generated.Our research findings provide theoretical support for understanding and controlling topological states in quasiperi-odic and quasicrystalline systems.
Objective.The Titanium:sapphire-on-insulator(Ti:SaOI)platform provides a brand new route to realize ultra-broadband tunable integrated lasers.To get high efficiency,the amplifier design must be treated carefully to handle the pump and signal light well.Here,we study the optical characteristics of Ti:SaOI waveguide amplifiers and do a systematic geometric opti-mization.The target is to maximize the optical gain and push down the lasing threshold.This work is expected to offer theoretical supports for fabricating high-performance on-chip Ti:sapphire lasers. Methods.We use the multi-physics finite element method to do the numerical simulation.First,mode field analysis is applied.By doing this,the critical bending radius and the single-mode cutoff condition are found to avoid light leakage.After that,a coupled rate equation model is built.We use it to check how the waveguide width affects two competing parameters:the mode confine-ment factor and the effective mode area.Besides,we also look at the waveguide length to see its effect on both the small-signal gain and the large-signal saturation output during the light propagation. Results and discussions.From the mode analysis,we get the safe boundaries for single-mode working.The rate equation simula-tion shows a clear competition.A narrower width makes the effective mode area smaller,which is good for pump intensity,but it drops the confinement factor at the same time.Balancing these things,the device works best when the width is 1.0 μm and the length is 2.0 cm.Using this exact size,we simulated the gain spectrum covering the 700 to 950 nm band.The result points out a very good broadband amplification.The peak gain is increased by about 16 dB compared to the reported experimental data.This increase proves our model works and shows the great potential of the Ti:SaOI platform for wideband applications. Conclusions.Optimizing the geometry is very useful for improving the amplifier performance.We also set up a semi-analytical model to calculate the laser threshold based on the best parameters we found.The calculation tells us that our new waveguide design can reduce the threshold pump power a lot.In short,the findings in this paper give clear design rules and theoretical help for future experiments on ultra-broadband,low-threshold on-chip Ti:sapphire lasers.
Objective.This work aims to build a theoretical framework to simulate one-dimensional Anderson localization within a periodically driven cavity quantum electrodynamics(QED)system.By using the discrete Fock-space structure found in the Jaynes-Cummings model,we attempt to map the Floquet dynamics of this circuit QED setup onto an effective tight-binding model.This mapping then allows us to control and mimic localization and delocalization behavior by adjusting external driving parameters. Methods.We focus on a resonantly coupled atom and single-mode cavity described by the Jaynes-Cummings Hamiltonian.The atom experiences a periodic sequence of pulses;each Floquet period consists of a rotation followed by Jaynes-Cummings evolu-tion lasting a specific time.The single-period Floquet operator is formed by multiplying the rotation operator and the Jaynes-Cummings evolution operator in sequence.We expand the Floquet eigenstates in the photon-number basis,which leads to coupled recurrence relations for the amplitudes of ground and excited states.Applying a nearest-neighbor closure approximation,we remove the excited-state amplitudes and derive an effective difference equation for the ground-state amplitudes alone.This equa-tion has the form of a 1D inhomogeneous tight-binding model,where the photon number plays the role of lattice sites,parameter-dependent coefficients act like hopping amplitudes connecting neighboring sites,and a site-dependent term functions as an effec-tive potential. Results and Discussions.Numerical simulations were done by iterating the Floquet operator repeatedly,starting from the initial condition with the atom in the ground state and no photons.We tracked the photon-number distribution and the mean photon number as indicators of localization.Over a broad range of rotation angles and interaction durations,the mean photon number tended to remain much smaller than the number of evolution steps,suggesting diffusion suppression typical of Anderson localiza-tion.The probability distributions mostly stayed concentrated at low photon numbers,with dominant population in the lowest pho-ton states.Yet,for certain parameter choices,the behavior shifted,showing delocalized transport where probabilities rapidly spread to higher photon-number states and the mean photon number approached the step count.Overall,this demonstrates that the driven cavity QED system can emulate both localized and delocalized regimes,with control over the transition via pulse parameters. Conclusions.We show that a cavity QED system under periodic pulsing offers a practical platform for simulating 1D Anderson localization in Fock space.The Floquet dynamics naturally map onto a generalized Anderson model with parameter-dependent hopping and effective disorder potentials.Numerical evidence indicates localization prevails over most parameters,but delocaliza-tion emerges in certain regions,allowing dynamical switching through external control.This approach provides a clear theoretical picture,good experimental tunability,and aligns well with current quantum technology.Importantly,the framework can be extended to account for detuning,dissipation,quasi-periodic drives,and multi-qubit setups—opening up possibilities for explor-ing richer localization phenomena,nonequilibrium phase transitions,and many-body Floquet quantum simulation.
Objective.Photons serve as excellent carriers for quantum information.The generation of single photons with high retrieval efficiency facilitates the entanglement distribution rate in long-distance quantum communication.The Duan-Lukin-Cirac-Zoller(DLCZ)protocol based on atomic ensembles not only enables the generation of single photons but also supports the storage of quantum states,which inherently provides a natural advantage in temporal synchronization.In this work,we employ the cavity-enhanced DLCZ protocol to prepare heralded single-photon sources with high retrieval efficiency in an 87Rb cold atomic ensemble. Methods.We first prepare the atoms in the ground state|5S1/2,F=1,m=-1>,and then apply a write pulse to stimulate the sponta-neous Raman scattering process,generating correlated pairs of Stokes photons and atomic spin waves.The successful detection of Stokes photons heralds the creation of atomic spin waves.After a programmable delay,a read pulse is applied to convert the spin waves into anti-Stokes photons,thereby realizing the experimental preparation of heralded single-photon sources.In the experi-ment,we construct a ring cavity around the atomic ensemble to enhance the conversion efficiency from spin waves to single pho-tons.The dependence of the retrieval efficiency on the storage time is measured,and furthermore,the effects of the storage time t and the write excitation rate x on the autocorrelation function of the anti-Stokes photons α are investigated. Results and Discussions.By utilizing cavity-enhanced technology,we increase the conversion efficiency from spin waves to pho-tons to 48％.The autocorrelation function of the prepared optical field is less than 1 when t＜100 μs(x=1％)orx＜8％(t=1 μs),which maintains the anti-bunching effect of single photon sources.In the next step,we aim to further improve the intrinsic retrieval efficiency of single photons by reducing intracavity losses and optimizing the resonance between the anti-Stokes photons and the cavity.Meanwhile,we also plan to improve the practical retrieval efficiency of single photons by designing a high signal-to-noise ratio filtering system and optimizing the fiber coupling efficiency. Conclusions.The results show that we prepare single-photon sources with the intrinsic retrieval efficiency of 48％and the storage lifetime of 100 μs based on the cavity-enhanced DLCZ protocol.This research provides an experimental foundation for the prepa-ration of high-quality single-photon sources based on the DLCZ protocol.
Objective.Ultraviolet radiation is an important component of solar radiation.Ultraviolet radiation has a variety of important applications,including high-resolution light sources,phototherapy,disinfection,sterilization,deodorization,organic decomposition,photocatalysis,gas sensing,optical dialysis dose monitoring,identification of harmful agents,and more.However,at present,metamaterial absorbers are mainly used in microwave,infrared and visible light frequency bands,and there are relatively few absorbers that can cover the 200～400 nm ultraviolet frequency band.Therefore,it is of great significance to carry out the research on the perfect absorber of broadband metamaterials for the ultraviolet band.In addition,our goal in design-ing this ultraviolet absorber is to create a design that can adapt to various environments,has a simple structure,and achieves high absorption efficiency. Methods.In this paper,Nickel(Ni)metal is selected as the absorbing material,and an ultraviolet(UV)absorber is designed based on a simple metal-insulator-metal(MIM)structure.Figure 1 illustrates the unit structure of the MIM-type ultraviolet absorber based on Ni metal,which is a two-dimensional grating absorber arranged horizontally with P periods.The cell structure consists of a dielectric layer of silicon dioxide(SiO2)with a height of h2,grown on an Ni metal substrate with a thickness of h1.On top of this,a Ni metal pattern layer with a thickness of h3 is formed.This pattern layer is composed of two parts:the outer ring and the inner structure.The outer radius is designated as R,while the inner radius is r1.The internal structure consists of a hollow cylinder with a radius of r2,which is etched inside an Ni metal rectangular cuboid that has a height of h3 and a width of L.Additionally,half air cylinders with a radius of r3 are etched on the four sides of the rectangular cuboid.The finite element method(Comsol Multiphysics™ 5.4)is used to simulate the designed absorber.In the calculation,the minimum grid size used isλ/20,and the maximum grid size is λ/5. Results and Discussions.It is found through a large number of numerical simulations that the optimal parameters of the absorber are as follows:unit period P=400 nm,Ni metal substrate height h1=170 nm,SiO2 dielectric height h2=50 nm,upper Ni pattern height h3=180 nm,upper Ni pattern outer radius R=200 nm,inner ring radius r1=185 nm,inner cavity radius r2=40 nm,pattern layer inner pattern outer semicircle radius r3=85 nm.The side length of the internal original cube is L=255 nm.Under the condition of using the optimal parameters,when the angle of incidence is zero,the average absorption of the absorber can reach more than 90％in the wavelength range of 200～400 nm.Notably,the absorption rate exceeds 95％within the 200～250 nm wavelength range,300～325 nm and 375～400 nm.At 220 nm,the absorption reaches a maximum of 98.8％.Across the 200～400 nm spectral band,the absorption rate remains above 90％.Over a broad range of incident angles(0～50o)and wavelengths(200～400 nm),the average absorption rate maintains above 90％.Due to their rotational symmetry,UV absorbers can achieve polarization-insensitive effects. Conclusions.A novel MIM structured UV absorber consisting of Ni metal,SiO2 dielectric,and Ni metal layers was introduced in this article.Through the finite element method analysis,it is found that the structure can efficiently absorb ultraviolet rays with a wavelength of 200～400 nm,with an absorption efficiency of more than 90％,and the structure is not affected by the angle of incidence and polarization.This design simplifies the manufacturing process and improves absorption efficiency,which is expected to be used in areas such as UV detection,protection,and lithography.
