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

We implement a technique for measuring the singlet-triplet energy splitting responsible for spin-to-charge conversion in semiconductor quantum dots. This method, which requires fast, single-shot charge measurement, reliably extracts both large and small splittings. We perform this technique on an undoped, accumulation-mode Si/Si-Ge triple-quantum dot and find that the measured splitting varies smoothly as a function of confinement gate biases. Not only does this demonstration prove the value of having an in situ excited-state measurement technique as part of a standard tune-up procedure, but it also suggests that in typical Si/Si-Ge quantum-dot devices, spin blockade can be limited by lateral orbital excitation energies rather than valley splitting.