Masters defense: Bertram Seck Brovang

Multi-gate control of quantum-point-contact potentials in GaAs Hall bars 

I present the fabrication and measurement of a top-gated GaAs/AlGaAs quan- tum device, designed to investigate algorithm-based tuning of quantised conductance and quantum Hall states. The device consists of a GaAs Hall bar with a high-mobility two- dimensional electron gas (2DEG), on which a pixel-like array of gate electrodes is fabricated in such a fine geometry that a tunable quantum point contact (QPC) can be induced in the 2DEG. Importantly, the presence of up to 17 gate electrodes allows application of up to 17 independent gate voltages, with is far beyond the control capability of prior quantum- point-contact devices. To demonstrate the resulting tunability of the potential landscape experienced by the electron gas, we apply a new tuning algorithm that optimizes for observ- ing a quantized conductance staircase without human intervention. I also present magnetic field measurements in the quantum Hall configuration, with an outlook towards applying multi-gate quantum point contacts in future integer and fractional quantum Hall experiments. 

Zoom: https://ucph-ku.zoom.us/j/65415894449?pwd=Sk9uRUhXdDdibHRpQ0M5WFRyMGl1UT09

Meeting ID: 654 1589 4449
Passcode: 896100