Sequential Quantum Gate Decomposer (SQUANDER)

The Sequential Quantum Gate Decomposer (SQUANDER) package provides a novel solution to decompose any n-qubit unitary into a sequence of one-qubit rotations and CNOT gates. SQUANDER utilizes a new gate synthesis technique that applies periodic layers of CNOTs and parametric one-qubit gates to an n-qubit unitary such that the resulting unitary is 1-qubit decoupled, i.e., is a tensor product of an (n-1)-qubit and a 1-qubit unitary. Continuing the decoupling procedure sequentially one arrives at the end to a full decomposition of the original unitary into 1- and 2-qubit gates. SQUANDER provides lower CNOT counts for generic n-qubit unitaries (up to n=7) than the previously provided upper bounds.