  To push commercial electronics beyond its current size limits, atomic-scale
communication channels and logic units need to be designed, making the use of
quantum entities an imperative. In this regime, quantum fluctuations naturally
become prominent, and are generally considered to be detrimental. Here we show
that for spin-based information processing, these fluctuations can be uniquely
exploited to gate the flow of classical binary information across a magnetic
chain. Moreover, this information flow can be controlled with a modest external
magnetic field that drives the system through different many-body quantum
phases in which the orientation of the final spin does or does not reflect the
orientation of the initial input. Our results are general for a wide class of
anisotropic spin chains that act as magnetic cellular automata, and suggest
that quantum fluctuations may play a unique role in driving classical
information flow at the atomic scale.
