  We present a proposal for a one-bit full-adder to process classical
information based on the quantum reversible dynamics of a triple quantum dot
system. The device works via the repeated execution of a Fredkin gate
implemented through the dynamics of a single time-independent Hamiltonian. Our
proposal uses realistic parameter values and could be implemented on currently
available quantum dot architectures. We compare the estimated energy
requirements for operating our full-adder with those of well-known fully
classical devices, and argue that our proposal may provide a consistently
better energy efficiency. Our work serves as a proof of principle for the
development of energy-efficient information technologies operating through
coherent quantum dynamics.
