Engineering electrical control of single donor flip-flop qubits for universal quantum computations*

The "flip-flop" qubit is composed of the ↑↓ / ↓↑ states of the electron and nucleus spin of an implanted ³¹P atom [1] in Si. It enables fast 1-qubit gates through the electrical modulation of the hyperfine interaction, achieved by hybridizing the orbital states of the donor electron with a quantum dot at the Si/SiO₂ interface. Biasing the electron wavefunction towards the interface creates a large electric dipole allowing for long distance coupling between donors, which mediates 2-qubit logic gates. Coherent control of the flip-flop states of an ¹²³Sb donor has been demonstrated, in a non-optimized device. Here we present the progress in developing a CMOS compatible nanostructure, designed to enable accurate electric control of the hyperfine interaction (for coherent driving), and tunability on the coupling to charge reservoirs (for state readout). We report gated control of electron tunnel times of interface dots to a nearby read-out quantum dot by nearly two orders of magnitude. We further investigate the effects of our high-frequency electrical antenna on the coherent control of both electron and nuclear spins.
[1] G. Tosi et al., Nat. Commun. 8, 450 (2017).