  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.
