Nanoscale quantum transport for quantum information processing
Qassemi Maloomeh, Farzad
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In this thesis, I study quantum transport of electron (e.g., current and noise) in quantum dots exploring microscopic processes responsible for spin-relaxation in double quantum dots in Pauli spin blockade regime. This is a regime where current is blocked due to the spin configuration of electrons in the dot. The Pauli spin blockade provides a means for preparation, manipulation and readout in spin qubits. Hence, understanding the underlying mechanism which lifts this blockade is extremely important. First, I have developed a theory of spin-flip cotunneling (higher order tunneling) processes in double quantum dots in the Pauli spin blockade regime. Utilizing this theory, I have calculated the full analytical dependence of the stationary current on applied magnetic fields, gate voltages, and an inter-dot tunnel coupling in Pauli spin blockade. This work is important for understanding the nature of leakage, especially in systems where other spin-flip mechanisms (due, e.g., hyperfine coupling to nuclear spins or spin-orbit coupling) are weak, including silicon and carbon nanotube or graphene quantum dots. This theory explains recent experiments on carbon nanotubes and silicon double quantum dot. In addition, I propose a new scheme based on the current noise to probe spin relaxation mechanisms in double quantum dot in the Pauli spin blockade regime, where spin-selection rule applies. As a result, I provide a simple closed-form expression which can be used to fit experimental data to extract multiple spin-relaxation rates, even at very low energy splitting. This method allows for the characterization of different aspects of decay process in these systems.
Cite this work
Farzad Qassemi Maloomeh (2013). Nanoscale quantum transport for quantum information processing. UWSpace. http://hdl.handle.net/10012/7451