CQC2T Seminar (UNSW Sydney): A silicon quantum-dot-coupled nuclear spin qubit

Speaker – Dr Wister Huang:

Nuclear spins in the solid state have long been envisaged as a platform for quantum computing, due to their long coherence times and excellent controllability. Measurements can be performed via localized electrons, for example those in single atom dopants or crystal defects. In quantum dots, on the other hand, the electron wavefunction typically overlaps with many nuclear spins, leading to undesired effects such as loss of coherence and spin relaxation. However, tunable interdot electron tunnelling allows direct coupling of electron spin-based qubits in neighbouring dots and compatibility with semiconductor fabrication techniques provides a compelling route to scaling to large numbers of qubits.

Here we show that for electrons in silicon metal–oxide–semiconductor quantum dots the hyperfine interaction is sufficient to initialize, read-out and control single silicon-29 nuclear spins, yielding a combination of the long coherence times of nuclear spins with the flexibility and scalability of quantum dot systems. We demonstrate high-fidelity projective readout and control of the nuclear spin qubit, as well as entanglement between the nuclear and electron spins. Crucially, we find that both the nuclear spin and electron spin retain their coherence while moving the electron between quantum dots, paving the way to long range nuclear-nuclear entanglement via electron shuttling. Our results establish nuclear spins in quantum dots as a powerful new resource for quantum processing.