# Coherent transfer of quantum information in silicon using resonant SWAP gates

## TL;DR

This paper demonstrates a high-fidelity, phase-coherent resonant SWAP gate in silicon quantum dots, enabling coherent transfer of quantum states and extending qubit connectivity for scalable quantum computing.

## Contribution

The authors introduce a novel single-step resonant SWAP gate in silicon quantum dots, achieving coherent spin transport and benchmarking its fidelity for the first time.

## Key findings

- Achieved a 98% average fidelity for spin state transfer in 100 ns.
- Demonstrated transfer of arbitrary two-qubit states with 84% fidelity.
- Enabled coherent coupling of non-adjacent qubits in silicon quantum processors.

## Abstract

Solid state quantum processors based on spins in silicon quantum dots are emerging as a powerful platform for quantum information processing. High fidelity single- and two-qubit gates have recently been demonstrated and large extendable qubit arrays are now routinely fabricated. However, two-qubit gates are mediated through nearest-neighbor exchange interactions, which require direct wavefunction overlap. This limits the overall connectivity of these devices and is a major hurdle to realizing error correction, quantum random access memory, and multi-qubit quantum algorithms. To extend the connectivity, qubits can be shuttled around a device using quantum SWAP gates, but phase coherent SWAPs have not yet been realized in silicon devices. Here, we demonstrate a new single-step resonant SWAP gate. We first use the gate to efficiently initialize and readout our double quantum dot. We then show that the gate can move spin eigenstates in 100 ns with average fidelity $\bar{F}_{SWAP}^p$ = 98%. Finally, the transfer of arbitrary two-qubit product states is benchmarked using state tomography and Clifford randomized benchmarking, yielding an average fidelity of $\bar{F}_{SWAP}^c$ = 84% for gate operation times of ~300 ns. Through coherent spin transport, our resonant SWAP gate enables the coupling of non-adjacent qubits, thus paving the way to large scale experiments using silicon spin qubits.