  Synthesis of quaternary quantum circuits involves basic quaternary gates and
logic operations in the quaternary quantum domain. In this paper, we propose
new projection operations and quaternary logic gates for synthesizing
quaternary logic functions. We also demonstrate the realization of the proposed
gates using basic quantum quaternary operations. We then employ our synthesis
method to design of quaternary adder and some benchmark circuits. Our results
in terms of circuit cost, are better than the existing works.
