Experimentally Investigation Of Quantum Control Based On Trapped Ion System

Quantum mechanics,which mainly describes the laws of matter in the micro world,is considered as the two cornerstones of modern physics together with the theory of relativity.Since the second quantum mechanics revolution,benefiting from the im-provement of technology,quantum communication,quantum metrology and quantum computation based on principles of quantum mechanics have been greatly developed.In recent years,the concept of Noisy Intermediate-Scale Quantum(NISQ)technology is proposed.In order to apply quantum technology to practical problems in sociology,it is necessary to effectively and accurately control the quantum system of medium scale.At present,there are many promising platforms to explore quantum information process in the world,among which the trapped ion system has received a lot of attention due to its outstanding advantages,such as long coherent time,identical quantum bits and effective coupling of any two qubits.In this thesis,we have built a needle ion trap and carried out a series of research on quantum control,including:(1).Experimental demonstration of suppressing residual geometric dephasing.The dephasing of quantum systems is a very difficult obstacle to carry out accurate quan-tum control and improve the fidelity of quantum gates.Traditional dynamic decoupling methods can effectively suppress the dephasing of fynamics,but they can not supress geometric dephasing.Based on the evolution of quantum system,we design a method to improve the dynamic decoupling,which can effectively suppress the dynamics and geometric dephasing.The decoherence of qubit under Gaussian noise is explored in the two-level system of a trapped ion.It is verified that the modefied dynamic decou-pling method can reduce decoherence rate by more than one order of magnitude than the traditional method.(2).Experimental realization of nonadiabatic holonomic single-qubit quantum gates with optimal control in a trapped ion.Quantum gates based on geometric phase have natural anti noise properties.However,in previous proposal,geometric phase quantum gates have to be implemented adiabatically.The limited coherent time of the system ofter limits the anti noise properties of geometric phase quantum gates.Using the three-level structure of trapped ion,we develop a method to realize nonadiabatic holonomic quantum gates.This method is more robust to the rabi frequency error than previous geometric quantum gates.(3).Experimentally verifying anti-Kibble-Zurek behavior in a quantum system under noisy control field.Kibble-Zurek(KZ)mechanism is a universal framework to describe the phase transition process.However,some phenomena violating KZ mech-anism have been observed in the field of ferromagnetic phase transition in recent years.Because it is difficult to effectively control the parameters in the process of phase tran-sition,there are few experiments in this area.We quantitatively explore the relationship between the noise intensity and the defects in the phase transition process by using the mixing Gaussian noise in microwave and controllable two-level system in driving ions.(4).Experimentally realizing efficient quantum control with reinforcement learn-ing.By using reinforcement learning method and the effective control time of shortcut to adiabatic(STA)as a priori imformation,we develop a fast and robust quantum control method.Different from the waveform which needs to be changed continuously in the adiabatic path,we design a digital multi pulse waveform to complete specific quantum tasks.The experimental results show that the proposed method is robust to both rabi frequency errors and detuning errors.