Quantum Plain and Carry Look-Ahead Adders
  In this paper, two quantum networks for the addition operation are presented. One is the Modified Quantum Plain (MQP) adder, and the other is the Quantum Carry Look-Ahead (QCLA) adder. The MQP adder is obtained by modifying the Conventional Quantum Plain (CQP) adder. The QCLA adder is an extension of conventional digital Carry Look-Ahead adder. Compared with the CQP adder, two main advantages are as follows: First, the proposed MQP and QCLA adders have less number of elementary gates than the CQP adder. Secondly, the number of processing stages of the MQP and QCLA adder are less than ones of the CQP adder. As a result, the throughput time for computing the sum of two numbers on the quantum computer can be improved. 
Kai-Wen Cheng, Chien-Cheng Tseng