Few-body properties of interacting spins in III-V semiconductors

Open Access
Author:
Woodworth, Ryan
Graduate Program:
Physics
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
July 02, 2009
Committee Members:
  • Gerald Dennis Mahan, Dissertation Advisor/Co-Advisor
  • Gerald Dennis Mahan, Committee Chair/Co-Chair
  • Nitin Samarth, Committee Member
  • Vincent Henry Crespi, Committee Member
  • Venkatraman Gopalan, Committee Member
Keywords:
  • semiconductor microdisk lasers
  • spin exchange scattering
  • charge diffusion
  • encoded quantum computation
Abstract:
We perform theoretical analyses of several novel device applications which make use of the distinctive electronic and optical properties of III-V semiconductors. Electron spins in semiconductor quantum dots are a promising candidate for the physical realization of a solid-state quantum computer. Whenever three or more spins interact simultaneously, the system's full Hamiltonian is found to include nonlinear interactions that significantly influence its dynamics in experimentally relevant parameter regimes. We consider the implications of these results for the proposed implementations of known quantum algorithms; in particular, we describe a method for circumventing the four-body effects in an encoded system (four spins per logical bit) by the appropriate tuning of material parameters. We calculate the spin coherence lifetime of a conduction electron in a semiconductor due to exchange scattering from neutral donors. The average lifetime is computed in two and in three dimensions using the Born approximation. We find that, for realistic values of the impurity concentrations, these lifetimes are comparable to those of spin decoherence mechanisms commonly ascribed to experimentally observed lifetimes. We also develop a numerical model for charge diffusion in a GaAs heterostructure laser. We construct and solve rate equations for conduction electrons coupled to a single optical cavity mode in a microdisk. Our results extend previous theoretical approaches to diffusion and are consistent with applicable experiments.