Strong electron-electron interactions in Si/SiGe quantum dots

Abstract

Interactions between electrons can strongly affect the shape and functionality of multi-electron quantum dots. The resulting charge distributions can be localized, as in the case of Wigner molecules, with consequences for the energy spectrum and tunneling to states outside the dot. The situation is even more complicated for silicon dots, due to the interplay between valley, orbital, and interaction energy scales. Here, we study two-electron wavefunctions in electrostatically confined quantum dots formed in a SiGe/Si/SiGe quantum well at zero magnetic field, using a combination of tight-binding and full-configuration-interaction (FCI) methods, and taking into account atomic-scale disorder at the quantum well interface. We model dots based on recent qubit experiments, which straddle the boundary between strongly interacting and weakly interacting systems, and display a rich and diverse range of behaviors. Our calculations show that strong electron-electron interactions, induced by weak confinement, can significantly suppress the low-lying, singlet-triplet (ST) excitation energy. However, when the valley-orbit interactions caused by interfacial disorder are weak, the ST splitting can approach its noninteracting value, even when the electron-electron interactions are strong and Wigner-molecule behavior is observed. These results have important implications for the rational design and fabrication of quantum dot qubits with predictable properties.

22 pages, 11 figures

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• Low disorder and high valley splitting in silicon
• How valley-orbit states in silicon quantum dots probe quantum well interfaces
• Mapping of valley-splitting by conveyor-mode spin-coherent electron shuttling
• Strong hole-photon coupling in planar Ge for probing charge degree and strongly-correlated states
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• Spin-orbit enhancement in Si/SiGe heterostructures with oscillating Ge concentration
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• High-precision real-space simulation of electrostatically-confined few-electron states
• Non-reciprocal Pauli Spin Blockade in a Silicon Double Quantum Dot
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• Valleytronic full configuration-interaction approach: An application to the excitation spectra of Si double-dot qubits
• Wigner-molecularization-enabled dynamic nuclear field programming
• Theory of multi-dimensional quantum capacitance and its application to spin and charge discrimination in quantum-dot arrays
• Charge-noise resilience of two-electron quantum dots in Si/SiGe heterostructures
• Path integral simulation of exchange interactions in CMOS spin qubits
• Crystal-field effects in the formation of Wigner-molecule supercrystals in moiré TMD superlattices
• Robust entangling gate for capacitively coupled few-electron singlet-triplet qubits
• Microscopic theory on magnetic-field-tuned sweet spot of exchange interactions in multielectron quantum-dot systems
• Sign-switching of superexchange mediated by few electrons under non-uniform magnetic field
• Ab initio modelling of quantum dot qubits: Coupling, gate dynamics and robustness versus charge noise
• Electronic Correlations in Multielectron Silicon Quantum Dots
• Dressed basis sets for the modeling of exchange interactions in double quantum dots
• Towards Utilizing Scanning Gate Microscopy as a High-Resolution Probe of Valley Splitting in Si/SiGe Heterostructures
• Anomalous zero-field splitting for hole spin qubits in Si and Ge quantum dots
• Effects of rotation on the thermodynamic properties of a quantum dot