Quantum contextuality of a qutrit state

We present a study of quantum contextuality of three-dimensional mixed states for the Klyachko-Can-Binicioğlu-Shumovsky (KCBS) and the Kurzyński-Kaszlikowski (KK) noncontextuality inequalities. For any class of states whose eigenvalues are arranged in decreasing order, a universal set of measurements always exists for the KK inequality, whereas none exists for the KCBS inequality. This difference can be reflected from the spectral distribution of the overall measurement matrix. Our results would facilitate the error analysis for experimental setups, and our spectral method in the paper combined with graph theory could be useful in future studies on quantum contextuality.

Figure 1

The exclusivity graph of (a) KCBS and (b) KK.

Figure 2

The upper (blue) and lower (red) bounds of $C_q$ of mixed states for (a) KCBS and (b) KK, where $A(0,\sqrt{5}),B(\frac{3}{40}(11-\sqrt{5}),2),C(\frac{3}{4},2)$, $D(1,\frac{5}{3})$, $E(0,10/3),F(2/3,29/9),G(1,3)$.

Figure 3

The curve of $(m_1,m_2)$ for (a) KCBS and (b) KK, where $A(2,2)$, $B(\sqrt{5},\frac{5-\sqrt{5}}{2})$, $C(3,3)$, $D(\frac{10}{3},3)$.

Figure 4

The violation $C_q$ of diagonal states for KCBS, where $A,B,C$ stands for pure states $|1\rangle ,|3\rangle ,|5\rangle$, respectively, and each point in the triangle stands for a mixed state which is a convex mixture of $|1\rangle ,|3\rangle ,|5\rangle$. The inner white region is the set of states which do not violate the classical bound 2.