Thermal behavior of quantum cellular automaton wires

We investigate the effect of finite temperature on the behavior of logic circuits based on the principle of quantum cellular automata (QCA) and of ground state computation. In particular, we focus on the error probability for a wire of QCA cells that propagates a logic state. A numerical model and an analytical, more approximate model are presented for evaluation of the partition function of such a system and, consequently, of the desired probabilities. We compare the results of the two models, assess the limits of validity of the analytical approach, and show that error probabilities depend on the ratio of the energy splitting between the ground state and first excited state to the thermal energy kT. We then provide estimates of the maximum operating temperature for a few relevant cases, and discuss possible approaches for increasing it. (C) 2000 American Institute of Physics. [S0021-8979(00)01310-4].