Closed expressions for one-qubit states of convex roof coherence measures

Abstract

We study the closed expressions of the convex roof coherence measures for one-qubit states in this paper. We present the analytical expressions for the convex roof coherence measures, $C_f(\rho)$, of one-qubit states with $C_f(\varphi):=f(\abs{c_0}^2,\abs{c_1}^2)$ (where $\ket{\varphi}=c_0\ket{0}+c_1\ket{1}$) being convex with respect to the $l_1$ norm of coherence of $\varphi$ (i.e., $C_{l_1}(\varphi)$), such coherence measures including the coherence of formation, the geometric measure of coherence, the coherence concurrence, and the coherence rank. We further present the operational interpretations of these measures. Finally, we present the usefulness of the convex roof coherence measures $C_f(\varphi)$ being non-convex with respect to $C_{l_1}(\varphi)$ by giving the necessary and sufficient conditions for the transformations $p\varphi_1\oplus(1-p)\varphi_2\to q\phi_1\oplus(1-q)\phi_2$ via incoherent operations, where $\varphi_i$, $\phi_j$ $(i, j=1, 2)$ are one-qubit pure states and $0\leq p, q\leq 1$.