Lifting of spin blockade by charged impurities in Si-MOS double quantum dot devices

One obstacle that has slowed the development of electrically gated metal-oxide-semiconductor (MOS) singlet-triplet qubits is the frequent lack of observed spin blockade, even in samples with large singlet-triplet energy splittings. We present theoretical and experimental evidence that this problem in MOS double quantum dots can be caused by stray positive charges in the oxide, inducing accidental localized levels near the device's active region that lead to the lifting of the spin blockade. We also present evidence that these effects can be mitigated by device design modifications, such as overlapping gates.