On Estimating Quantum Divergences with $p$-Power Means

Abstract

We study the problem of estimating the quantum divergence with $p$-power means, $Φ_p(ρ\,\|\,σ)$. This quantity was investigated by Lam and Le (\textit{Linear Algebra Appl.}\ 2021). For any constant $p \in (0, 1)$, we present sample-efficient and query-efficient quantum algorithms for estimating $Φ_p(ρ\,\|\,σ)$ and further show that estimating $Φ_p(ρ\,\|\,σ)$ is $\mathsf{BQP}$-complete in the low-rank case.