Experimental Research On Multi-Mode Coupled Quantum Entanglement

With the development of theory and technology,quantum information science has brought development opportunities to a series of related technologies,not only in the field of quantum computation,it also has broad application prospects in the fields of quantum communication,quantum simulation,and quantum sensing.As the most ma-ture quantum information experimental platform,linear optical system has a good de-velopment prospect.In the future practical composite quantum network,photons,as the optimal flying qubits will be used to connect experimental platform such as trapped ions,neutral atoms,superconducting systems,and solid color centers to realize quantum information transfer among various nodes.Many degree of freedoms of photon have been used to encode information,includ-ing polarization,path,frequency,time-bin and orbital angular momentum,etc.While single mode based information encoding method brings the convenience of simplify-ing theoretical models and experimental devices,it also exposes experiments to a series of problems such as the loss of information carried by photons,weak interaction be-tween photons,and the inability to integrate the advantages of different modes.Study-ing the coupling of different modes can effectively solve these problems,realizing ex-pansion of the scale of photon systems,coherent information transformation between different modes,entangled measurement between modes,and the simulation of open quantum dynamics.These are of great importance to fulfill the potential of photonic systems in quantum information science.This thesis will focus on photonic mode cou-pling and study its applications in the preparation of high-dimensional entangled states,measurement-device-independent verification of high-dimensional quantum nonlocal-ity,quantum communication with indefinite causal orders,and simulation of multi-time quantum memory effect.The main contents include:1.To remove the characterizations on the measuremental apparatus,we developed an experimentally friendly high-dimensional quantum refereed steering witness game.In the experiment,we constructed a hybrid entangled source encoded in photonic polar-ization and path degree of freedoms,further expanded the photon path space to prepare"question states",and realize high-dimensional Bell state measurement between polar-ization and path modes.Our experiment results verified 3-dimensional quantum steer-ing in a measurement-device-independent way.As an application,the observed data in the experiment is used to generate quantum randomness.With two measurement settings,we extract 1.106±0.023 bits of private randomness per every photon pair,which surpasses the one-bit limit for projective measurements performed on qubit sys-tems.This work is the first valid experimental demonstration on measurement-device-independent quantum information processing tasks beyond qubits.2.By studying genuine multi-level entanglement and irreducible dimensionality of entanglement,we explored the particular structure of high-dimensional entanglement.For genuine multi-level entanglement we realized the witness of genuine three-and four-dimensional entangled states and observed three-and four-dimensional quantum correlations that cannot be simulated with two-dimensional systems.However,the wit-ness of genuine multi-level entanglement still relies on the assumption on measurement apparatus.To solve this problem,we introduced the concept of irreducible entangle-ment and proved that the quantitative measurement-device-independent entanglement witness can detect the irreducible entanglement of the system.We then demonstrated this protocol with a 3-level bipartite entangled state and quantified a lower bound of its generalized robustness that exceeded the bound of 2-dimensional systems,presenting the existence of irreducible 3-dimensional entanglement.This work provides a good template for the study of high-dimensional quantum correlations.3.We constructed an optical quantum switch using photonic polarization and path mode,designed a phase-locking system to greatly improve the phase stability of the quantum interference,and realized quantum communication protocols with channels arranged in a superposition of two alternative causal orders.We experimentally ob-served classical information transmission through two completely depolarizing chan-nels and quantum information transmission through entanglement-breaking channels,effectively verifing the communication advantages of superposed causal orders.This is the first proof-of-principle experimental demonstration of quantum communication beyond standard quantum Shannon theory,and represented an important step in the second quantization of Shannon theory.In addition,this novel quantum resource also has important applications for other quantum information processes,such as quantum computation,quantum metrology,and simulation of quantum space-time.4.We explored multi-time quantum memory effects with a multi-qubit entangle-ment source.Two three-step non-Markovian processes were simulated,and a variety of POVM were realized based on quantum walks.The experimental results showed that the two processes have different Markov orders under different instruments.In partic-ular,certain POVMs can block the memory effects of non-Markovian processes,and based on this,we effectively predicted the expected values of some observ-ables on these quantum stochastic processes.This experiment provide the first demon-stration of multitime quantum memory effects beyond the two-time setting and the re-sults fully demonstrated the instrument-specific nature of quantum memory.