Self Assembled Semiconductor Quantum Dots for Spin Based All Optical and Electronic Quantum Computing

Abstract

Abstract : This project involved the study of self-assembled quantum dots as hosts for spin based qubits. Both semiconductor quantum dots, nanowires, and organic quantum dots were studied and the spin relaxation times were measured. The organic Alq3 appears to have very long longitudinal spin relaxation time of nearly 1 second at a temperature of 100 K, and a nearly temperature independent transverse relaxation time > 3 nsec in the range 2-300 K. This relaxation time is sufficient to fulfill the Knill criterion for fault-tolerant quantum computing at room temperature. Since organics have special selection rules for radiative transitions whereby triplet electron-hole pairs are dark excitons and only singlets are radiative, there is a natural qubit read out scheme for organic quantum dots. We have also studied inorganic semiconductor quantum dots, but find them inferior to their organic counterparts for spin based quantum computing, primarily because spin-orbit interactions are much stronger in inorganic quantum dots, leading to much faster spin dephasing.