The Research And Application Of Closed-loop Learning Control Based On Nuclear Magnetic Resonance System

The birth of quantum mechanics is one of the greatest revolutions in human's history of science.It completely changes our understandings on microcosm,promotes the progress of many fields,including physics,chemistry and information science,and in-duces a series of evolutionary technologies,e.g.,laser,nuclear energy and semiconductor.With the establishment of information science and the sophistication of controlling quantum system,we do not only understand quantum theories by observing quantum phenomenons,but try to build quantum devices that directly obey the quantum theory,thus bring us unprecedented technology revolutions over the classical technology limit.The resulting quantum technology,including quantum computation,quantum metrology,quantum simulation and quantum communication,has made substantial process,though still suffers tremendous challenges.The fragile properties and uncertainties of quantum system make it easily affected by surroundings,and it's further hampered by the exponentially increasing complexity of the system freedoms.Researching how to maintain the quantum properties meanwhile achieve high-quality quantum control in noisy systems is crucial for realizing the aforementioned quantum technology.People have developed many strategies to defend against various perturbations in environments,thus leading to efficient and accurate realizing of our control targets.Closed-loop learning control is a convenient and general method among them.Previously,closed-loop learning is widely used in the experiments of quantum chemistry.At present,its researches are mainly concentrated on preparing high-fidelity quantum states and gates.However,quantum technology demands higher requirements of the precision and robustness of the control target,thus also bring problems for closed-loop learning control,such as the low efficiency of learning algorithms and the complexity of evaluating the control target.In this context,this thesis focuses on closed-loop learning control,then introducing the author's work of applying this method to the fields of quantum computation,quantum control and quantum metrology.Mainly it includes the following three parts:1.We propose an improved differential evolutionary algorithm,then successfully apply it to the preparation of Bell state and CNOT gate,realizing better precision and robustness over classical ways;We propose a closed-loop gradient-based algorithm that can efficiently measure the gradients experimentally,then success-fully apply it to the preparation of seven-qubit coherent state.This method provides a promising approach to precisely control large-scale quantum system.2.We use differential evolutionary algorithm and pulse smoothing technique to de-sign a method for optimizing adiabatic quantum pathways,then compare it with conventional methods in typical adiabatic quantum computation problems,the results suggest that the proposed method performs better,which is likely to be applied to more complex and more realistic adiabatic quantum computation problems.3.We propose a practical probe state optimization method for quantum metrology based on closed-loop learning control,then perform numerical simulations and experiments for sensing the phase of spin chains.The proposed method is scal-able,and it can avoid the exponentially increasing resource that conventional methods needed for designing the optimal probes.Moreover,it can adaptively involve the experimental noise,thus is a great choice for automatically designing the optimal probes for quantum metrology.The researches here strengthen our understanding of the performances of closed-loop control in various control applications in quantum technology.They are very helpful for improving the efficiency of closed-loop learning itself,thus making steps towards applying it to more complex and large-scale control tasks.As the progress of closed-loop learning control,together with the developing of many other control methods,we believe that the realization of expected quantum technology will bring us tremendous revolutions of production and life.