Study On Of Strong Coupling Between Optical Force Based On Surface Plasmon And Quantum System

The study of the coupling between an optical microcavity and a quantum system has always been an important scientific topic in the field of quantum information.When the coherent energy exchange rate between the optical microcavity and the quantum system exceeds their energy dissipation rate,the system reaches in the strong coupling regime.The energy states of the strong coupling system show the characteristics of partial photons and partial matter,which enable the strong coupling system to be an important platform for studying quantum effects and therefore to exhibit wide application prospect in the fields of quantum communication and quantum computing.However,the optical diffraction limit prohibits the strong coupling system in the traditional optical microcavity from meeting the requirements of integration for quantum information processing.Plasmonic nanocavity based on metal nanostructures can break through the diffraction limit and has the ability to manipulate the light at the subwavelength scale,which effectively solves the above problems and becomes an ideal system to study the strong coupling effect at the nanoscale.Achieving the strong coupling between a plasmonic nanocavity and a single molecule level quantum system is the basis of many quantum operations,and has significant scientific value,and also faces several challenges.The first and foremost challenge is to precisely locate the single molecule level quantum system in the plasmonic nanocavity,and to achieve the deterministic coupling and interaction between the microcavity and the quantum system.With the development of optical tweezers technology,plasmonic nanotweezers becomes an effective means to solve the determinate coupling of quantum system in the plasmonic nanocavity.In this thesis,we design plasmonic nanostructures which can trap single-molecule quantum system,and study the strong coupling interaction between the plasmons and trapped single molecule quantum system.The main research contents of this thesis are as follows:1.A sub-wavelength periodic hole array structure is proposed.This structure supports both a propagating surface plasmon mode in the surface of the structure and a localized surface plasmon mode at the edge of the hole.The coupling of the two modes forms a blue detuned optical trap near the surface,which can trap a molecule.The coupling of the trapped single molecule and the plasmonic cavity is investigated.It is found that the strong coupling phenomenon can be observed only when the polarization of a single molecule is in the same direction with that of the incident light,whereas the phenomenon cannot be observed when the polarization of a single molecule is in other directions.This is due to the fact that the collective effect of the single molecule along the other directions is too strong and subsequently inhibits the coupling of the molecule and the plasmonic structure.In addition,different circularly polarized light is adopted to trap chiral molecules in the blue detuning capture system.Under the excitation of different circularly polarized light,the trapped chiral molecules interact with the plasmonic structure.In the transmission spectrum,the chiral fragmentation and chiral recovery are detected,the phenomenon of which can be explained by the theory of coherent superposition of electric field polarization vectors.2.A plasmonic tweezers structure composed of a gold ring and a bowtie antenna is proposed.This structure can trap a single J-aggregates molecule and also serve as a plasmonic cavity to investigate strong coupling interaction between light and matter.The bowtie nanoantenna can localize the electromagnetic field in the gap,and the combination of the bowtie antenna and the ring can further localize and enhance the electric field in the gap,so as to provide enough optical force to trap a J-aggregates molecule.The trapped J-aggregates molecule can affect the electromagnetic field distribution of the plasmonic tweezers through self-induced back action,thus improving the trapping efficiency.The strong coupling process between the trapped J-aggregates molecule and the plasmonic cavity is analyzed by using the coupled oscillator model,and the relationship among the optical force,the mode volume and the coupling strength of the system is studied.According to theoretical analysis,the number of excitons involved in the strong coupling is at the low exciton number level,which is close to the quantum optical limit,and the virtual exciton theory is used to explain the strong coupling process at the low exciton number level theoretically.3.The chiral optical responses of a single chiral molecule and the chiral optical response of a strong coupled system of a chiral molecule and a silver nanorod is studied.The chiral molecule is composed of helically arranged quantum dots,whose chiral optical response is determined by the dipole interactions between the quantum dots and asymmetric arrangement of the quantum dots.Using a silver nanorod and the chiral molecule to form coupled hybrid systems,in the strong coupling regime,the strong coupling process and the plasmon field enhancement effect can accelerate the energy transfer and enhance the absorption of the system,improving the system’s chiral optical response.This method provides a scheme for the design of novel plasma nanostructures with a strong chiral optical response.