The Modulation And On-chip Integration Of Single Photon Emitters In Two-dimensional Materials

Modulation and integration of single photon emitters(SPEs)hold great significance in fields such as quantum communication and quantum information processing,representing a challenging and promising frontier of research.Currently,the research on deterministic SPEs still faces challenges such as high efficiency,low noise,ease of integration,and fabrication.To achieve high-performance requirements in practical applications,it is necessary to modulate and optimize SPEs and investigate how to integrate them with optical structures.The scalability,mode matching,and stability of optical quantum circuits based on spatial optics are limited,hindering the large-scale and practical application of optical quantum systems.One potential solution is to integrate optical components on the platform into photonic chips,also known as quantum photonic chips.Research on SPEs based on quantum dots has become quite mature;however,only the indium arsenide(InAs)quantum dots embedded in a gallium arsenide(GaAs)can currently meet the requirements for use in quantum key distribution in experiments.Unfortunately,this material imposes numerous constraints on integrated optical platform materials.Fortunately,in recent years,the continuous discovery of highbrightness SPEs in two-dimensional(2D)materials with thicknesses less than 1 nm has facilitated their integration and modulation with various optical structures.Notably,it has been found that SPEs in monolayer or few-layer hexagonal boron nitride(h-BN)can work at room temperature.This paper is devoted to studying the modulaton of arbitrary SPEs and the integration of monolayer 2D materials with optical waveguides.The main achievements include:utilizing surface plasmon polaritons to achieve efficient near-field collection fluorescence from quantum dot SPEs while enhancing the fluorescence;preparing SPEs from different materials and employing probes with silver nanowires to collect and modulate SPEs with different orientations in the near field;transferring monolayer 2D materials onto a lithium niobate thin film and successfully integrating them into the chip using the mechanism of bound states in the continuum,laying the experimental foundation for realizing stable transmission of integrated quantum light sources.The specific research content includes the following aspects:1.Achieving brightness enhancement and the high-efficiency collection of SPEs based on surface plasmon polaritonsSurface plasmon polaritons have a small mode volume and can be used to modulate light-matter interactions.We utilize an integrated near-field probe consisting of a fiber taper and silver nanowire to enhance and collect the fluorescence of SPEs.We chose cadmium selenide(CdSe)quantum dot SPEs as the subject of our study,as they exhibit better interaction with surface plasmon polaritons.When positioning the probe at a distance of 20 nm from the SPE,we observed a rapid enhancement of light-matter interaction,and the single-photon signal could be collected by the near-field probe.Moreover,numerical results show that its collection efficiency can be optimized to over 10%.This scheme provides a flexible way to modulate the emission of SPEs.2.Achieving controllable lifetime modulation of SPEs with different orientations based on surface plasmon polaritonsBy modulating light-matter interactions,the quality of SPEs can be improved.We conducted an in-depth investigation of the controllable modulation of the radiative properties of SPEs with different orientations using a probes with silver nanowires.We prepared CdSe quantum dots and h-BN defect SPEs with different orientations for our experiments.For the SPEs with out-of-plane orientations,their radiative lifetime can be reduced by 70%;for those with in-plane orientations,their average modulation amplitude of lifetime is 0.69 to 1.23.The experimental results are in excellent agreement with simulations and theoretical predictions,providing an effective method for optimizing the performance of SPEs.3.Achieving low-loss on-chip photonic routing by the integration between a monolayer 2D material and an etchless lithium niobate filmOn-chip light sources are essential components of scalable photonic integrated circuits.We sandwich a monolayer 2D material between a lithium niobate thin film(with a high refractive index)and a polymer waveguide(with a low refractive index).By designing a suitable waveguide width,the fluorescence from the 2D material can be bounded within the thin film(with the bound states in the continuum mode),and transmitted along the waveguide with a low loss.This approach reduces manufacturing costs and complexity while avoiding damage to the two-dimensional material.Experimentally,we demonstrated that the photoluminescence of a monolayer tungsten disulfide(WS2)can be coupled into the waveguide and propagate with a bound state in the continuum mode.For in-plane oriented dipoles,numerical simulations obtained a coupling efficiency of about 2.3%with a near-zero loss at 620 nm wavelength.For out-of-plane oriented dipoles,coupling efficiency of up to 10.9%can be achieved in the simulation.This work breaks through the limitations of integrating 2D materials with conventional optical structures(with TM mode),opening up new avenues for light-matter coupling in monolithic photonic integrated circuits,and laying the technical foundation for realizing low-loss on-chip SPEs.The innovative points of this thesis are as follows:1.We proposed using silver nanowire probes to modulate SPEs,and experimentally achieved precise fixed-point operation of the probes.The collection efficiency of the probe has been improved by at least two orders of magnitude compared to conventional metal-coated near-field probes.2.We have conducted a detailed theoretical and experimental study on the strong polarization dependence of coherent modulation by the silver nanowire probes for SPEs,providing a new scheme for in-situ modulation of SPEs,which is an important step toward on-demand modulation and practical applications related to the SPEs’s performance.3.We proposed using the bound states in the continuum mechanism to achieve integratable 2D material-based on-chip quantum light sources,and experimentally verified the feasibility of this idea.This not only eliminates the need for etching high-refractiveindex materials but also enables low-loss routing of on-chip photons.