Experimental Research Of Quantum Entanglement Based On Photonics System

Quantum entanglement is the most significant feature of the quantum world.It first came into people’s sight as ’spooky action at a distance’,causing fierce debates on ’reality’,’locality’ and ’completeness of quantum mechanics’,and then verified the correctness of quantum mechanics with the introduction of Bell inequality.Through the long-term efforts of researchers all over the world,quantum entanglement has gradually developed from theory to experiment and become the core of quantum information applications,such as quantum computation,quantum communication,quantum precision measurement,quantum simulation and so on.However,there are still many important but unsolved problems of quantum entanglement.Photonic systems have been considered as one of the best systems for studying quantum entanglement due to its advantages of easy manipulation and low noise.In photonic systems,by taking advantage of its multi-degree-of-freedom,through certain nonlinear transformation and linear transformation,the preparation of various quantum states including multi-photon entanglement can be completed.Then we can explore the entanglement properties by measuring these quantum states.In this dissertation,we have studied the properties of quantum entanglement theoretically and experimentally based on photonic systems,and explored related applications of quantum entanglement by combining weak measurement and classical algorithms.The main achievements are as follows:1.The invariants of three-body entanglement,the tradeoff relation of twobody entanglement(correlation)in multiparticle entanglement.Multi-body entanglement,the relationship between quantum entanglement and other correlations are two important topics in quantum entanglement.On the one hand,we measure isotropic and anisotropic invariants of three-qubit quantum states,and establish quantitative relations with Horodecki parameters and entanglement sequences respectively.On the other hand,by preparing and measuring the three-qubit quantum state and the four-qubit classical-classical state,we study two tradeoff relations:the tradeoff relation between internal entanglement and external entanglement,and the tradeoff relation between internal entanglement and external classical correlation.We also give quantitative inequalities under different metric choices.2.Quantum non-locality multi-party sharing.Quantum non-localilty multiparty sharing is of great significance in quantum network,generation of quantum randomness,one-sided quantum key distribution and so on.It is usually realized by constructing sequence measurement model with the help of weak measurement.The Bell non-localilty and Einstein-Podolsky-Rosen steering in one-sided model have been proved theoretically and realized experimentally.Here,we consider the two-sided model with four observers for the first time.We present the steering parameter formulas in the case of unbiased measurement,and observe the double EPR steering experimentally.3.The simulation of the two-site Fermi-Hubbard model.Quantum computation is one of the main applications of quantum entanglement.Because universal quantum computation has serious requirements on qubit number,gate fidelity and error correction,a method combining classical optimization algorithms and near-term quantum systems was proposed.We prepared the ansatz state with unknown parameters in the photonic system and iterated the parameters according to the optimization algorithm untill convergence.After iteration we obtained the ground state and excited state of two-site Fermi-Hubbard model,and then we measured the transition amplitude to calculate the corresponding Green function.4.Optical realization of multi-degree-of-freedom coupling system.As a typical topological structure,skyrmions are often formed in magnetic materials and thin film systems.They are prime candidate for realizing high-speed memory.Inspired by quantum entanglement,we coupled the polarization state and the orbital angular momentum state of photons to construct the optical skyrmions in free space.We calculated the corresponding topological number-the skyrmion number,and analyzed its noise robustness.