Theoretical Study Of Quantum Control On Solid-state Spin System

Quantum computing utilizes the principles of quantum mechanics.On some issues,such as large-number decomposition,quantum computing has great advantages over its classical conterpart.However,there are still many challenges to physically realize large-scale quantum computing.Decoherence is one of the important difficulties that must be overcome.It affects the storage,operation,transmission and other processes of quantum information.A variety of methods for suppressing decoherence have been proposed,such as quantum error correction,decoherence-free subspace,and dynamic decoupling.Scalability is another important issue in quantum computing.In 1998,Kane proposed a semiconductor-based scalable quantum computing architecture.With the advancement of technology,more and more excellent candidate systems have entered people's sights,such as doped fullerene with different atoms and nitrogen-vacancy(NV)centers in diamond.Scalability is still one significant direction that many researchers are studying and exploring.Based on the quantum control of a solid-state spin system,which is one of the important candidate systems for quantum computing,we propose a new method to suppress decoherence and a scalable quantum computing architecture.This dissertation first introduces the basic concepts of quantum computing,and then introduces the NV center system in diamond.The central content of this dissertation is divided into the following two aspects:1.A new method for suppressing decoherence by optimal control of a spin bath is proposed.Different from the existing methods of suppressing decoherence,which mostly focus on the quantum system itself,we focus on the environment.Via optimally control the spin bath to"freezes"the bath,the coherence time of the central spin can be extended.Through numerical simulations,we demonstrate the feasibility of the method.The simulation results show that the coherence time of the central spin can be increased from 4?s to 1 ms,and the effect of suppressing the decoherence is obvious.At the same time,this method can be compatible with DC magnetic field detection.In simulations the sensitivity of DC magnetometry is dramatically improved by 1 order of magnitude to nT/(?)by our method.It has broad applications in quantum metrology.2.A new scalable quantum computing architecture is proposed.Combined with the decoherent-free subspace(DFS)qubit and quantum actuator,we realize the initialization,readout and universal quantum gates of the DFS qubits through the control of a single quantum actuator,and discusse the scalability.We numerically simulate the above processes,and verify the feasibility.In this method,the difficulty of directly controlling a large number of qubits through the classical interface is simplified to the control of a single quantum actuator,which provides a new method to deal with complex quantum systems.