Precision tomography of silicon donor qubits at the threshold of fault tolerance

Abstract: Last year, the cover of Nature announced “Silicon qubits cross key error-correction threshold for quantum computing”. I’ll explain [some of] the science behind this claim, and its context within the current explosive growth of quantum computing science and technology. In that issue of Nature, three independent papers reported broadly similar experimental demonstrations. I’ll focus on one of the others, co-authored by experimentalists from UNSW (Sydney) and theorists from Sandia’s Quantum Performance Lab (QPL). I’ll explain the basic physics of the 3-qubit electronuclear device created at UNSW, and then I’ll explain how we (the QPL) achieved complete, precise characterization of six logic gates on two donor-atom nuclear spin qubits, to demonstrate error rates below 1%. If time permits, I'll try to peel back the curtain and explain why characterizing qubit gate error rates in a way that actually sheds light on the viability of error correction is really tricky.