Reducing Reversible Circuit Cost by Adding Lines

Additional lines are required to implement an irreversible function as a reversible circuit. The emphasis, particularly in automated synthesis methods, has been on using the minimal number of additional lines. In this paper, we show that circuit cost reductions can be achieved by adding additional lines. We present an algorithm for line addition that can be targeted to reducing the quantum cost of a circuit or the transistor count for a CMOS implementation. Experimental results show that the cost reduction can be significant even if (1) only a small number of lines (even one) is added and (2) other circuit optimizations have already been applied.