# A silicon quantum-dot-coupled nuclear spin qubit

## TL;DR

This paper demonstrates the control, readout, and entanglement of silicon-29 nuclear spins in quantum dots, combining long coherence times with scalable quantum dot technology, and enabling long-range nuclear spin interactions.

## Contribution

It shows that hyperfine interactions in silicon quantum dots are strong enough for nuclear spin control, enabling scalable quantum computing with long coherence times.

## Key findings

- High-fidelity nuclear spin readout and control achieved.
- Entanglement demonstrated between nuclear and electron spins.
- Electron shuttling preserves spin coherence, enabling long-range interactions.

## Abstract

Single 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 localised electrons, for example those in single atom dopants or crystal defects. However, establishing long-range interactions between multiple dopants or defects is challenging. Conversely, in lithographically-defined quantum dots, tuneable interdot electron tunnelling allows direct coupling of electron spin-based qubits in neighbouring dots. Moreover, compatibility with semiconductor fabrication techniques provides a compelling route to scaling to large numbers of qubits. Unfortunately, hyperfine interactions are typically too weak to address single nuclei. Here we show that for electrons in silicon metal-oxide-semiconductor quantum dots the hyperfine interaction is sufficient to initialise, 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.