We show how single quantum dots, each hosting a singlet–triplet qubit, can be placed in arrays
to build a spin quantum cellular automaton. A fast (∼10 ns) deterministic coherent singlet–triplet
filtering, as opposed to current incoherent tunneling/slow-adiabatic based quantum gates
(operation time ∼300 ns), can be employed to produce a two-qubit gate through capacitive
(electrostatic) couplings that can operate over significant distances. This is the coherent version
of the widely discussed charge and nano-magnet cellular automata, and would increase speed,
reduce dissipation, and perform quantum computation while interfacing smoothly with its
classical counterpart. This combines the best of two worlds—the coherence of spin pairs known
from quantum technologies, and the strength and range of electrostatic couplings from the
charge-based classical cellular automata. Significantly our system has zero electric dipole
moment during the whole operation process, thereby increasing its charge dephasing time.