Exchange Coupling in a Linear Chain of Three Quantum-Dot Spin Qubits in Silicon

Quantum gates between spin qubits can be implemented leveraging the natural Heisenberg exchange interaction two electrons in contact with each other. This is controllable by electrically tailoring overlap electronic wavefunctions quantum dot systems, as long they occupy neighbouring dots. An alternative route exploration of superexchange - coupling remote spins mediated a third idle electron that bridges distance We experimentally demonstrate direct and provide evidence for second neighbour linear array three single-electron silicon, inferred from resonance frequency spectra. confirm theoretically through atomistic modeling device geometry only allows sizeable dots, while next nearest cannot stem vanishingly small tail wavefunction possible if mediated.