  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.
