Spin-Blockade Spectroscopy of Si / Si - Ge Quantum Dots

Singlet-triplet spin states of a quantum dot support promising semiconductor-based qubits, yet often suffer from poor state preparation and measurement, due to low-lying excited states. Engineering a large energy splitting is impeded by the inability to accurately measure both large and small energy splittings with the device biased to nominal operation. The authors present a measurement and fitting approach that accurately extracts both large and small splittings in this regime. They also find evidence that both orbital and valley degrees of freedom may set this energy separation, significantly affecting which paths to pursue in device design.