Maxwell’s demon and quantum-dot cellular automata

Quantum-dot cellular automata ~QCA! involves representing binary information with the charge configuration of closed cells comprised of several dots. Current does not flow between cells, but rather the Coulomb interaction between cells enables computation to occur. We use this system to explore, quantitatively and in a specific physical system, the relation between computation and energy dissipation. Our results support the connection made by Landauer between logical reversibility and physical reversibility. While computation always involves some energy dissipation, there is no fundamental lower limit on how much energy must be dissipated in performing a logically reversible computation. We explicitly calculate the amount of energy that is dissipated to the environment in both logically irreversible ‘‘erase’’ and logically reversible ‘‘copy-then-erase’’ operations carried out in finite time at nonzero temperature. The ‘‘copy’’ operation is performed by using a near-by QCA cell which plays the role of Maxwell’s demon. The QCA shift register can then be viewed as a sequence of copy-then-erase operations where the role of the demon cell shifts down the line. © 2003 American Institute of Physics. @DOI: 10.1063/1.1581350#