Coupled Double Quantum Dot Devices, Electronic Spin States Of Quantum Measurement

Quantum measurement of single electron spin states is an important topic in both fundamental aspects and potential applications of quantum information processing. In this thesis, we study the readout of single electron spin states in a double quantum dots (DQD) using a quantum point contact (QPC).In Chapter 1, we briefly review the quantum dot system and its physical properties such as quantum size effect, Coulomb blockade, Pauli spin blockade and quantum tunneling. Some of the concepts in this Chapter serves as the framework of the subsequent chapters.In Chapter 2, we introduce the basic knowledge regarding the readout the of single electron spin states. It includes the physical principle of single electron spin resonance and its experimental implementation, the Fermi contact hyperfine interaction between an electron spin in a quantum dot and many nuclear spins in the host material, and the application of the rate equations approach in electron transport through quantum dot.In Chapter 3, we present our main results. First, we briefly introduce experimental results obtained by others for the single electron spin readout in single quantum dot. Then, we study the dynamics of a single electron spin in a DQD and its readout via QPC. We model the system microscopically and derive rate equations for the reduced electron density matrix of the DQD. Two cases with one and two electrons in the DQD are studied. In the one-electron case (studied in Chapter 3), the electron spin states are distinctly characterized by a constant and an oscillatory current through the QPC. Moreover, to ensure that an electron is properly injected into the qubit dot, we propose to determine the success of the electron injection from the variations of the QPC current after applying an oscillating magnetic field to the qubit dot.In Chapter 4, we study the two-electron case, where the readout of the spin state of the electron in one of the dots called the qubit dot is essentially similar after considering hyperfine interactions between the electrons and the nuclear spins of the host materials and a uniform magnetic field applied to the DQD. Same as in the one-electron case, we determine the success of the electron injection again from the variations of the QPC current after applying an oscillating magnetic field to the qubit dot. Finally, we give a brief summary in Chapter 5.