  Quantum information science has the potential to revolutionize modern
technology by providing resource-efficient approaches to computing,
communication, and sensing. Although the physical qubits in a realistic quantum
device will inevitably suffer errors, quantum error correction creates a path
to fault-tolerant quantum information processing. Quantum error correction,
however, requires that individual qubits can interact with many other qubits in
the processor. Engineering this high connectivity can pose a challenge for
platforms like electron spin qubits that naturally favor linear arrays. Here,
we present an experimental demonstration of the transmission of electron spin
states via Heisenberg exchange in an array of spin qubits. We transfer both
single-spin and entangled states back and forth in a quadruple quantum-dot
array without moving any electrons. Because it is scalable to large numbers of
qubits, state transfer through Heisenberg exchange will be especially useful
for multi-qubit gates and error-correction in spin-based quantum computers.
