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Events on Monday, March 8th, 2021

Electron-electron interactions in Si/SiGe Quantum Dots
Time: 2:00 pm
Speaker: Ekmel Ercan, Physics PhD Graduate Student
Abstract: In this talk I present our work on the effects of confinement strength on two-electron states in an electrostatically-defined quantum dot in a Si/SiGe quantum well at zero magnetic field, focusing on geometries appropriate for qubits. I will discuss that the experimental signatures of strong electron-electron (e-e) interactions in these devices can be subtle. While the suppression of the singlet-triplet splitting in two-electron quantum dots formed in direct band gap materials is a clear indication of e-e interactions, in silicon devices this effect can be masked by the additional valley degree of freedom of the conduction band electrons, when the quantum well interface is flat. I will further argue that interfacial-disorder-induced valley-orbit coupling, on the other hand, can induce this suppression. Next, I will discuss implications of this physics on charge noise sensitivity and demonstrate calculations indicating that dramatic changes in dephasing times can be observed by slightly changing the confinement strength. Finally, I will discuss the role of e-e interactions in two recent experiments demonstrating (1) the use of valley-orbit states to probe Si/SiGe interface, and (2) a spectroscopically-dense set of low-lying energy levels.
Host: Sue Coppersmith, Faculty Advisor
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