Coherent Spin-State Transfer via Heisenberg Exchange*

Spin qubits in semiconductors are a promising scalable architecture for quantum computing. Long chains of spin qubits have already been realized in different semiconductor platforms but transferring quantum information throughout such chains is still a challenge. Here we present the first experimental demonstration of the coherent transfer of electron spin states back and forth across a chain of four quantum-dot spin qubits using Heisenberg exchange coupling between neighboring electrons, which arises from the overlap of their wavefunctions. We swap the spin states of a pair of electrons via precisely-controlled exchange pulses. Successive SWAP operations between different pairs can transfer a quantum spin state to a distant qubit, without moving any electrons. Because this method is scalable to long chains of spin qubits, coherent spin -state transfer using Heisenberg exchange will be useful in multi qubit operations, measurement-based entanglement swapping and gate teleportation, and error correction in spin-based quantum computers.