Exact QSP angles for odd monomials

Abstract

We present an analytical solution to the angle-finding problem in quantum signal processing (QSP) for monomials of odd degree. Specifically, we show that to implement a monomial of degree \( n \), where \( n \) is odd, it suffices to choose powers of a primitive \( n \)-th root of unity as QSP phase angles. Our approach departs from standard numerical methods and is rooted in a group-theoretic argument. Being fully analytical, it eliminates numerical errors and reduces computational overhead in QSP implementation of odd monomials. Such use cases arise, for example, in quantum computing, where self-adjoint contractions are embedded into unitary operators acting on extended Hilbert spaces.