Highly Efficient Decomposition of n-Qubit Quantum Gates Based on Block-ZXZ Decomposition

This paper proposes a new optimized quantum block-ZXZ decomposition method [4,5,6] that results in the construction of more optimal quantum circuits than the quantum Shannon decomposition (QSD) [17] can achieve, which has been the most optimal decomposition method since 2006. With the proposed decomposition, a general 3-qubit gate can be decomposed using 19 CNOT gates (rather than 20). For general n-qubit gates, the proposed decomposition generates circuits that have (22/48) 4ⁿ - (3/2) 2ⁿ + (5/3) CNOT gates , which is less that the best known exact decomposition algorithm by (4ⁿ⁻² -1)/3 CNOT gates.