On-chip Generation And Manipulation Of Photonic Path Entanglement Based On An Optical Superlattice

Integrated quantum optics is a rapidly developing field in recent years, which helps people see the hope towards the practical quantum information processing. Integrated photonic chips, with all the optical elements integrated on a single chip, will be of benefit to quantum technologies for improved performance, miniaturization, and scalability. However, most of the photonic chips require external photon sources, which are usually bulky and involved with a lot of optical elements, thereby, as a further step towards integrated quantum optics, it is necessary to miniaturize the external photon sources for better performance. A solid strategy for achieving integrated quantum light sources turns to the traditional nonlinear optical crystals especially the optical superlattice. Optical superlattice acts as one of the most versatile and widely used materials for the generation of entangled photons, owing to strong quadratic nonlinearity and the state-of-the-art domain-engineering technique. By domain-engineering technique the spatial and temporal properties of entangled photons can be controlled inherently during the quasi-phase-matching (QPM) spontaneously parametric downconversion (SPDC) process, resulting in the direct generation of new types of photonic entanglement. More fortunately, thanks to the well-developed waveguide fabrication technique of lithium niobate, an on-chip integration of entangled photon sources together with waveguide circuits and phase shifters is on the way. In this dissertation, some integrated photon sources with special path entanglement and an on-chip integration of photon sources together with photonic circuits are studied. The dissertation is constructed as follows:1. We demonstrate the direct generation of a two-photon high-dimensional path entangled source from a single multi-stripe periodically poled lithium tantalate (MPPLT) crystal. We show two path entangled states with different spatial modes, one with a periodic amplitude modulation and the other with a periodic phase modulation, which are transferred from the transverse structures of MPPLT. Two-photon Talbot effect is theoretically predicted for the two entangled sources and experimentally observed using the one with periodic amplitude modulation.2. We demonstrate a multifunctional integrated photon source from a single two-dimensional optical superlattice, producing the heralded single-photon path entanglement and appealing beam-like two-photon path entanglement, which can be switched between each other by changing the temperature of the optical superlattice. We experimentally demonstrate the spatial Fourier spectrum of two entangled sources, and characterize the path entanglement by implementing quantum spatial beating experiments. Using cascaded domain structures the heralded single-photon path entanglement can be extended to a high-dimensional fashion, and a single-photon4-mode path entanglement is experimentally demonstrated.3. We demonstrate the on-chip generation and manipulation of photonic entanglement based on reconfigurable lithium niobate (LN) waveguide circuits. We confirm the validness of the fabrication technology for the LN photonic chip and do some improvement for better performance. The conversion efficiency of the PPLN waveguide photon source is measured, which has the same order of magnitude as the one reported in a reference paper. In order to characterize the on-chip manipulation of path entanglement, we carry out on-chip quantum interference experiments when varying the on-chip relative phase by electrooptical effect. We also perform an off-chip Hong-Ou-Mandel interference experiment to evaluate the entangled photons emit from the chip.