A universal quantum circuit for two-qubit transformations with three CNOT gates

摘要

We consider the implementation of two-qubit unitary transformations by meansof CNOT gates and single-qubit unitary gates. We show, by means of an explicitquantum circuit, that together with local gates three CNOT gates are necessaryand sufficient in order to implement an arbitrary unitary transformation of twoqubits. We also identify the subset of two-qubit gates that can be performedwith only two CNOT gates.