Experimental Chip-based Quantum Communication

Quantum communication,featuring its absolute security,is the key element of future communication network.However,current systems composed by bulk optical components are hard to be effectively extended,while integrated photonics show high reliability and applicability in manipulating size and flexibility of quantum systems.Thus,integrated photonics is now playing more and more important role in quantum communication.Several international groups have devoted years in research and accumulated valuable experimental results.As an emerging area,integrated photonics is still in fast development and has many unsolved problems,such as loss,stability,physical extendibility and load.As a result,it is quite important conducting research in chip-base quantum communication terminal.The goal of this project is to prepare terminal chips for quantum communication,realizing integrated and practical scheme of bulk optical components;set up testing platform for typical functional integrated photonic chips,such as beam focusing inspection,insertion loss,output mode and birefringence analysis;switch the chip into quantum communication network for feasibility feedback and end up with complete chip-based quantum communication terminal.The main work of this paper includes the following:First,the preparation of fundamental integrated photonic devices.Based on femtosecond laser direct writing technology,this paper implements the prepara-tion of on-chip single-mode waveguide,waveguide-based polarizing beam splitter,and creates novel rotated polarization directional couplers?which are able to make projections on arbitrary orthogonal states?,broadband polarization insensitive couplers and waveguide retarders.Second,novel quantum key distribution receiver chip based on the BB84 protocol.For the first time,a new broadband polarization insensitive coupler as well as rotated polarization directional couplers are connected in series on the same chip with stable phase.Projection measurements of the four polarization states in the BB84 protocol are realized,which is of great significance and practical value for the point-to-point quantum communication clients.Third,novel integrated server for quantum key distribution network.For the first time,this paper proposes and implements the integrated server for the star-type measurement device-independent quantum key distribution network.This paper designs and develops a quantum photonic chip that can integrate hundreds of high-performance Bell-state analyzers.Through proof-of-principle demonstration,this paper realizes 1.37×10^-6bits/pulse and 1.75×10^-6bits/pulse gain rates,0.058 and 0.081 quantum bit error rates for horizontal and diagonal bases.This work effectively proves the feasibility of integrated server and lays foundation for promoting the large-scale quantum internet.