Experimental Study On Optical Interface Based On Nanofibers And Cold Atoms

Controlling interactions between light and matters and achieving precision measurements in this process at quantum level is one of the central goals in experimental research and relevant applications of quantum optics.Neutral atom as a fundamental unit has provided an ideal platform for the research of light-matter interaction.Cooling and trapping neutral aotms in free space as well as manipulating single atoms until single atomic arrays precisely can offer the potential stage for demonstrating some phenomenon of fundamental quantum manipulations and quantum information processing,hence making the neutral-atoms-system-based optical interface as the node linking the storage and exchange of quantum information between photons and atoms become an improtant part,which has obtained long-term development in experiment.It also makes the photons-atoms interaction system exhibit the wide application prospects in many fields such as quantum information processing,non-linear optics and quantum metrology.For further experimental applications of photons-atoms interation system,it is of importance to improve the interaction strength betweeen them.The resonant scattering cross section of a single atom in free space is always at quare-of-wavelength level,hence the efficient coupling betweem photons and single atoms requires the confinement of photons to approach or even break the diffraction limit.In conventional light-atoms interfaces,vast macroscropic setups are used to trap and manipulate atoms in free space,which mainly consists of tightly focused beams,cavity quantum electrodynamics,atomic ensembles and Rydberg atoms,etc.Currently many successes have been obtained in these optical interfaces.However,the optical mode volume is still the limit in these setups,while the fundamental dissipation paths exhibited here are hard to be neglected.Owing to the existing mature field of micro and nano fabrication technologies,the experimental researches based on using micro and nano photonic devices to confine photons have experienced a long-term development in past more than ten years.Micro-nano photonic structures can provide a possible route toward robustness and scalability.As the ideal photon-confinement devices,it can confine photons in sub-wavelength region,hence decreasing the optical mode volume significantly.Compared to the conventional experimental systems,the micro-nano photonic structures docking with integrated quantum devices and quantum information precessing system possesses many advantages,therefore in recent years,the hybrid systems based on micro-nano photonic devices and neutral atoms has attracted lots of attentions.Moreover,duing to nature of fileds confined in micro-nano photonic structures,which is quite different than in free space,an increasing body of work has demonstrated a lot of novel phenomenonThe optical nanofiber waveguide with sub-wavelength diameter is one of the simplest nanophotonic structures,which can provide strong transverse confinement for guided light.Hence light propagating along the outer surface of a TOF is enhanced,called the evanescent field.The evanescent filed lies outside the nanofiber is confined in approximately half-wavelength region,which can be used to interact with single atoms and achieve efficient output.Moreover,the two-color dipole trap scheme based on evanescent field has also been implemented in experiment to load one-dimensional single atomic arrays in vicinity of nanofiber,which makes the nanofiber a significant approach to interface single atoms.Our laboratory started the experimental and theoretical researches of waveguide quantum electrodynamics based on nanofiber and cold atoms in recent years,and here I will introduce the work progress we have made in detail.The main parts of this thesis will include:1)We propose a simple hole-tailored nanofiber structure,which can be used to couple single dipole with high coupling efficiency.For specific polarization the coupling efficiency between nanofiber and single dipole can reach up to 62.8%,while the average coupling efficiency of three polarizations can reach 40%,which is almost two times that of the case of normal nanofiber.We study the coupling properties in this system,including the relations among the nanofiber diameter,hole diameter and the position,wavelength of the single dipole,which are also of importance in extending the single hole to a tailored periodic array for large-scale integrated quantum internet.Moreover,the feasibility of this system demonstrated in experiment is also disscussed here.2)In experiment we have built up the nanofiber-cold atoms coupling system,which includes the nanofiber fabrication system,ultra-high vacuum system,magneto-optical trap system and time-sequence control system.We realize the magnito-optical trap of Cesium atoms and efficient coupling between nanofiber and cold atoms.The nanofiber is used to collect the fluorescence emitted from cold atoms,and the power of which can reach up to 5×10~5 counts/s.We also use nanofiber to measure the absorption of cold atoms and obtain an absorption efficiency of approximately 7%.3)We have built up the two-color dipole trap system,and realized the loading of single atomic arrays in vicinity of nanofiber surface from magneto-optical trap.Using single atomic arrays we realize the absorption efficiency of 92%.We also measured the fundamental parameters of the two-color dipole trap,such as the lifetime of single atoms and the resonant vibrated frequency of single atoms in three dimensions.4)Based on the ready-made experimental setup we develop the optical heterodyne measurement system to measure the mechanical modes of nanofiber.We also use optical and mechanical stimulations to excite the mchanical modes of nanofiber.The thesis will introduce the priciple of the optical heterodyne measurement method and various of novel heterodyne measurement setups we have proposed.We have observed the flexural mode,longitudinal mode and torsional mode simultaneously withou any extra excitations.Furthermore,we introduce the optical and mechanical stimulations to excite the mechanical modes of nanofiber,and we can optomechanically realize the deterministic stimulations of flexural modes with specific frequencies.The effects of optical and mechanical stimulations with different modulated frequencies and exciting directions on nanofiber will be discussed here in detail.Theoretically we have calculated all four types of mechanical modes of nanofiber using numerical method and analytical method respectively,and we obtain the eigenmodes and resonant frequency relations of them.From the calculated results we can infer the localization properties of different types of mechanical modes of nanofiber.