Electron spins in few-electron lateral quantum dots
L. H. Willems van Beveren · 2005
This thesis describes a series of experiments aimed at understanding and controlling single electron spins confined in semiconductor lateral quantum dots, with the long-term goal of creating of a small-scale quantum computer. The confinement of these electrons results in a quantized energy spectrum, and therefore, the quantum dots can be regarded as artificial atoms. At first, the quantum dots are analyzed by conventional transport experiments. Here, we can energetically resolve the Zeeman splitting of a single electron when a strong magnetic field is applied. Excited-state spectroscopy enables us to identify the ground state spin configuration of a quantum dot containing 1-5 electrons. Furthermore, by using fast voltage pulses, we find a lower bound on the spin doublet relaxation time of 50 microseconds. Second, a novel method was developed for finding the relevant dot parameters in the regime of very weak dot-lead coupling. Here a quantum point contact electrostatically coupled to the quantum dot, is used as a fast and sensitive charge detector allowing us to resolve single-electron tunnel events in real time. Then, we demonstrate one of the key ingredients for a quantum computer: single-shot read-out of the spin states. To convert the spin information to charge information, we have exploited the spin-dependent energy, and spin-dependent tunnel rates, achieving a measurement visibility of more than 80%. Both for a single spin and for the two-electron spin states, we find that the relaxation can be very slow (relaxation times up to milliseconds). We find a strong magnetic field dependence that hints at spin-orbit interaction as the dominant