Generation Of Coherent Light Beams And High-Dimensional Path-Entangled States Based On Concurrent Parametric Down-Conversion Processes In 2D Optical Superlattice

The rapid developing of quantum communication and quantum computation technology puts forward urgent demand on quantum light source,which serves as the key resource of modern quantum information technology.Based on this,the dissertation presents effective methods to generate various quantum states through flexible domain engineering in 2D optical superlattice.2D optical superlattice can provide several collinear or noncollinear reciprocal-vectors simultaneously,thus allowing concurrent parametrnc down-conversion processes to take place coherently,resulting in superposition and leading to the direct output ot different quantum states.The scheme shows its advantages in integration,modulation and the potential of extending to higher dimensional Hilbert space.Meanwhile,concurrent parametric down-conversion processes can also provide coherent light beams,which has application in nonlinear frequency transformation.This dissertation studies the application of 2D optical superlattice as laser sources and quantum light sources of high-dimensional path-entanglement.This dissertation contains the following researches:1.We present a scheme of integrated monolithic source of terahertz wave.Transverse terahertz wave output is acquired through two cascading nonlinear processes in monolithic 2D optical superlattice.In the first down-conversion process,pump laser splits to near-degenerated signal and idler waves,then the quasi-phase-matching condition is satisfied by a noncollinear reciprocal vector,the interaction of signal and idler waves resulting in transverse terahertz wave output.We lay the superlattice in an optical cavity to accumulate the energy of near-degenerated signal and idler waves,thus leading to the efficient conversion of terahertz wave.We design the structure of 2D superlattice,and theoretically estimates the properties such as the conversion efficiency of the terahertz wave.2.The generation of path-entangled states and the potential in high-dimension extension in monolithic optical superlattice are discussed.2D superlattice can provide several noncollinear reciprocal vectors simultaneously,so as to open wide possibilities in entanglement modulation.This dissertation provides detailed characterization of the single photon distribution and two-photon correlation properties of several typical concurrence spontaneous parametric down-conversion processes,including the tuning of single photon spatial modes,parametric photon flux and the spatial correlation anisotropy which results from the noncollinear geometry.Besides,the method to generate high-dimensional path-entangled states is discussed.These research illuminates the potential of 2D superlattice as integrated photonic chips.3.Path-entanglement generation and modulation in superlattice waveguide chips is studied.Path-entangled states can be achieved by nonlinear quantum walk in waveguide arrays,this dissertation analyses the eigenmodes of three-coupled-waveguide system,and modulates the entangled state by pump laser amplitude,phase mismatch and coupling efficiency.The case of four-and five-waveguides-system is also discussed,extending the entanglement to higher dimensional Hilbert space.Entangled states generated in this way do not vary with the length of interaction,thus showing its advantages of stable,compact and effective4.A scheme of achieving heralded single photon source in waveguide chips is presented.Bright,high signal-noise ratio heralded single photon source is of great importance in quantum communication.In this dissertation,heralded single photons are generated by splitting the pump wave into several waveguides,and convert to parametric photons separately before combined again to become a heralded single photon source.Because splitting of the pump wave can be easily achieved in waveguide chips,parametric photons can be generated in as many as 32 waveguides,thus illuminating the potential of extending to higher dimension.This dissertation design structure of the chip and router,and test the generation of the frequency doubling process.