Quantum Circuit Based on Electron Spins in Semiconductor Quantum Dots

dc.contributor.authorHsieh, Chang-Yu
dc.description.abstractIn this thesis, I present a microscopic theory of quantum circuits based on interacting electron spins in quantum dot molecules. We use the Linear Combination of Harmonic Orbitals-Configuration Interaction (LCHO-CI) formalism for microscopic calculations. We then derive effective Hubbard, t-J, and Heisenberg models. These models are used to predict the electronic, spin and transport properties of a triple quantum dot molecule (TQDM) as a function of topology, gate configuration, bias and magnetic field. With these theoretical tools and fully characterized TQDMs, we propose the following applications: 1. Voltage tunable qubit encoded in the chiral states of a half-filled TQDM. We show how to perform single qubit operations by pulsing voltages. We propose the "chirality-to-charge" conversion as the measurement scheme and demonstrate the robustness of the chirality-encoded qubit due to charge fluctuations. We derive an effective qubit-qubit Hamiltonian and demonstrate the two-qubit gate. This provides all the necessary operations for a quantum computer built with chirality-encoded qubits. 2. Berry's phase. We explore the prospect of geometric quantum computing with chirality-encoded qubit. We construct a Herzberg circuit in the voltage space and show the accumulation of Berry's phase. 3. Macroscopic quantum states on a semiconductor chip. We consider a linear chain of TQDMs, each with 4 electrons, obtained by nanostructuring a metallic gate in a field effect transistor. We theoretically show that the low energy spectrum of the chain maps onto that of a spin-1 chain. Hence, we show that macroscopic quantum states, protected by a Haldane gap from the continuum, emerge. In order to minimize decoherence of electron spin qubits, we consider using electron spins in the p orbitals of the valence band (valence holes) as qubits. We develop a theory of valence hole qubit within the 4-band k.p model. We show that static magnetic fields can be used to perform single qubit operations. We also show that the qubit-qubit interactions are sensitive to the geometry of a quantum dot network. For vertical qubit arrays, we predict that there exists an optimal qubit separation suitable for the voltage control of qubit-qubit interactions.
dc.publisherUniversité d'Ottawa / University of Ottawa
dc.subjectQuantum Information Processing
dc.subjectSemiconductor Quantum Dots
dc.subjectStrongly Correlated Electronic System in Nanostructures
dc.subjectElectron Spin Qubits
dc.subjectQuantum Circuits
dc.subjectMesoscale and Nanoscale Physics
dc.titleQuantum Circuit Based on Electron Spins in Semiconductor Quantum Dots
dc.faculty.departmentPhysique / Physics
dc.contributor.supervisorHawrylak, Pawel
dc.degree.disciplineSciences / Science
thesis.degree.disciplineSciences / Science
uottawa.departmentPhysique / Physics
CollectionThèses, 2011 - // Theses, 2011 -