Electron Spins in Semiconductor Quantum Dots

Electron Spins in Semiconductor Quantum Dots

Hanson, R.

Kouwenhoven, L.P. (promotor)

Applied Sciences

2005-02-23

This thesis describes a series of experiments aimed at understanding and controlling the behavior of the spin degree of freedom of single electrons, confined in semiconductor quantum dots. This research work is motivated by the prospects of using the electron spin as a quantum bit (qubit), the basic building block of a quantum computer. Here, the envisioned basis states (logical 0 and 1) of the qubit are the two possible orientations of the spin in a magnetic field: spin-up (parallel to the field) and spin-down (anti-parallel to the field). In this thesis, a number of important steps towards the use of electron spins as qubits are reported: the isolation of a single electron in a quantum dot, energy spectroscopy of the electron spin states, development of a new technique to probe a nearlyisolated quantum dot, single-shot read-out of the electron spin orientation, and increased understanding of the interaction of the electron spin with its environment. A quantum dot can be thought of as a small box filled with a controllable number of electrons. This box is coupled via tunnel barriers to reservoirs, with which electrons can be exchanged, and is coupled capacitively to one or more gate electrodes that allow the number of electrons on the dot to be varied. Due to the small dot size (typically ? 50 nm), comparable to the Fermi wavelength of the electrons, it exhibits a discrete energy spectrum. The quantum dot devices studied in this work are defined in a two-dimensional electron gas (2DEG) of a GaAs/AlGaAs heterostructure, by applying negative voltages to metallic gate electrodes fabricated on top of the heterostructure.

electron spin
quantum dot
quantum information

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doctoral thesis

(c) 2005 R. Hanson