  Multi-controlled unitary gates have been a subject of interest in quantum
computing since its inception, and are widely used in quantum algorithms. The
current state-of-the-art approach to implementing n-qubit multi-controlled
gates involves the use of a quadratic number of single-qubit and CNOT gates.
However, linear solutions are possible for the case where the controlled gate
is a special unitary SU(2). The most widely-used decomposition of an n-qubit
multi-controlled SU(2) gate requires a circuit with a number of CNOT gates
proportional to 28n. In this work, we present a new decomposition of n-qubit
multi-controlled SU(2) gates that requires a circuit with a number of CNOT
gates proportional to 20n, and proportional to 16n if the SU(2) gate has at
least one real-valued diagonal. This new approach significantly improves the
existing algorithm by reducing the number of CNOT gates and the overall circuit
depth. As an application, we show the use of this decomposition for sparse
quantum state preparation. Our results are further validated by demonstrating a
proof of principle on a quantum device accessed through quantum cloud services.
