טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentPeniakov Giora
SubjectMagneto-optical Study of Semiconductor Quantum Dots
DepartmentDepartment of Physics
Supervisors Professor Daniel Podolsky
Professor David Gershoni
Full Thesis textFull thesis text - English Version


Abstract

Quantum dots are an experimental system that implements the concept of a “qubit” by a spin two-level system. Quantum dots are considered to be the best interface between flying qubits - photons, and matter anchored spin qubits. Since the two-level system is based on the spin degree of freedom, it is interesting to study how a control of this system can be achieved by applying external magnetic field. The interaction of magnetic field with spins is described by the Zeeman Hamiltonian. A g -factor is the proportionality factor between the applied magnetic field, and the energetic split that forms as a result, between spin up and down states.

We present an experimental study of the influence of externally applied magnetic field in the Faraday configuration on the photo-luminescence of single InAs/GaAs self-assembled quantum dot. We comprehensively study 17 well characterized optical transitions from the same, optically excited quantum dot in various charge and occupation states. In our measurements, the emitted light was in the direction of the magnetic field and along the symmetry axis of the quantum dot. The Zeeman splitting as well as the diamagnetic shifts of these transitions are accurately measured and analyzed. The measurements are then accurately fitted using 4 g -factors for ground and first excited energy levels of the confined electron and hole. While the g -factors of the ground levels agree with previous measurements, those of the excited levels are reported here for the first time, to the best of our knowledge. Surprisingly, the g -factor of the ground level heavy hole is reversed in sign from that of the excited heavy hole. Possible explanations for this sign reversal are discussed. These explanations consist of both numerical calculations and intuitive theoretical modification of an existing formula for g-factors in a bulk of a semiconductor. The spatial extension of the excitonic wave-function is evaluated from the measured values of the diamagnetic shift.