Valley Splitting in SiGe Quantum Dots Measured Using Pauli Blockade and Single-shot Readout

We introduce an in-situ technique to measure the valley splitting energy of SiGe quantum dots at the (2,0)-(1,1) charge boundary, the location of spin-to-charge conversion. Because the valley state is the lowest-energy excited state in many Si based spin qubits, low valley energies can limit the fidelity of both Pauli-blockaded spin readout and singlet initialization. In such systems, we can determine the valley splitting energy by measuring the extent of the Pauli blockade along the bias-voltage controlled detuning axis. In principle, this can be accomplished by comparing the behavior of the (1,1) singlet and (1,1) triplet states as they transition to the (2,0) charge state. Such an experiment would require both high fidelity initialization and calibrated spin rotations, which may be difficult to achieve when the valley splitting is small.
Our method leverages single-shot readout to measure dephasing-generated singlet and triplet transitions without either calibration or high-fidelity initialization. Using independently measured gate lever-arms and gate-to-gate capacitance ratios, we convert the separation between the spin-resolved transitions to an energy. We compare these single-shot measurements of valley splitting to those obtained using photon-assisted tunneling (PAT).