  Control of entanglement between qubits at distant quantum processors using a
two-qubit gate is an essential function of a scalable, modular implementation
of quantum computation. Among the many qubit platforms, spin qubits in silicon
quantum dots are promising for large-scale integration along with their
nanofabrication capability. However, linking distant silicon quantum processors
is challenging as two-qubit gates in spin qubits typically utilize short-range
exchange coupling, which is only effective between nearest-neighbor quantum
dots. Here we demonstrate a two-qubit gate between spin qubits via coherent
spin shuttling, a key technology for linking distant silicon quantum
processors. Coherent shuttling of a spin qubit enables efficient switching of
the exchange coupling with an on/off ratio exceeding 1,000 , while preserving
the spin coherence by 99.6% for the single shuttling between neighboring dots.
With this shuttling-mode exchange control, we demonstrate a two-qubit
controlled-phase gate with a fidelity of 93%, assessed via randomized
benchmarking. Combination of our technique and a phase coherent shuttling of a
qubit across a large quantum dot array will provide feasible path toward a
quantum link between distant silicon quantum processors, a key requirement for
large-scale quantum computation.
