Latched readout for the semiconductor quantum dot hybrid qubit

We explain and demonstrate a latched readout scheme for the semiconductor quantum dot hybrid qubit (QDHQ), working at the 5-electron (4,1)-(3,2) charge configuration. This configuration enables latching into either the (3,1) or the (4,2) charge states which can be detected with time-averaged or single-shot measurement. Here we demonstrate a single-shot measurement fidelity of 90.2% achieved using only a single electron reservoir for the double-quantum-dot pair; this will become increasingly important when scaling to larger arrays.  We also show that the 5-electron QDHQ has an improved readout window in gate voltage space when compared with the 3-electron QDHQ, which is sometimes limited by small valley splitting in Si/SiGe heterostructures. This combination of latched readout and an enhanced readout window in gate voltage space makes the 5-electron QDHQ a promising semiconductor quantum dot qubit with fast manipulation and a relatively long coherence time.