We propose an information -- theoretic framework for quantifying Kochen-Specker contextuality. Two complementary measures are introduced: the mutual information energy, a state-independent quantity inspired by Onicescu's information energy that captures the geometric overlap between joint eigenspaces within a context; and an operational measure based on commutator expectation values that reflects contextual behavior at the level of measurement outcomes. We establish a hierarchy of bounds connecting these measures to the Robertson uncertainty relation, including spectral, purity-corrected, and operator norm estimates. The framework is applied to the Klyachko-Can-Binicioğlu-Shumovsky (KCBS) scenario for spin-1 systems, where all quantities admit closed-form expressions. The Majorana-stellar representation furnishes a common geometric platform on which both the operational measure and the uncertainty products can be analyzed. For spin-1, this representation yields a three-dimensional Euclidean-like visualization of the Hilbert space in which, states lying on a plane exhibit maximum uncertainty for the observable along the perpendicular direction; simultaneous optimization across all KCBS contexts singles out a unique state on the symmetry axis. Notably, states achieving the optimal sum of uncertainty products exhibit vanishing operational contextuality, while states with substantial operational contextuality satisfy a nontrivial Robertson bound -- the two extremes are achieved by distinct quantum states.
We propose an information -- theoretic framework for quantifying Kochen-Specker contextuality. Two complementary measures are introduced: the mutual information energy, a state-independent quantity inspired by Onicescu's information energy that captures the geometric overlap between joint eigenspaces within a context; and an operational measure based on commutator expectation values that reflects contextual behavior at the level of measurement outcomes. We establish a hierarchy of bounds connecting these measures to the Robertson uncertainty relation, including spectral, purity-corrected, and operator norm estimates. The framework is applied to the Klyachko-Can-Binicioğlu-Shumovsky (KCBS) scenario for spin-1 systems, where all quantities admit closed-form expressions. The Majorana-stellar representation furnishes a common geometric platform on which both the operational measure and the uncertainty products can be analyzed. For spin-1, this representation yields a three-dimensional Euclidean-like visualization of the Hilbert space in which, states lying on a plane exhibit maximum uncertainty for the observable along the perpendicular direction; simultaneous optimization across all KCBS contexts singles out a unique state on the symmetry axis. Notably, states achieving the optimal sum of uncertainty products exhibit vanishing operational contextuality, while states with substantial operational contextuality satisfy a nontrivial Robertson bound -- the two extremes are achieved by distinct quantum states.
We place several known indicators of Kochen--Specker contextuality -- the KCBS correlator χ, the contextual fraction $\CF$, the Shannon-entropic n-cycle inequality of Chaves and Fritz, and the operational commutator witness D of Paper~I -- into a single projector-geometric framework organized around the overlap matrix $\Tcal_{ij} = d^{-1}\tr[(\hat P_i \hat Q_j)^2]$, where P^i and Q^j are the joint-eigenspace projectors of the two compatible observable pairs within a measurement context. The state-independent scalar content of $\Tcal$ is carried by two independent contractions: the mutual information energy $E = \sum_{ij}\Tcal_{ij}$ of Paper~I (equivalently, its logarithmic form S2=−log2E), and the Maassen--Uffink extremal overlap $c_\MU = \max_{i,j}|\langle a_i,b_i | c_j,b_j\rangle|$. We prove that S2 is non-increasing under coarse-graining, that $S_2(\Gcal) > 0$ is a necessary configuration-level condition for observable contextuality, and that the additive composition $S_2(\Gcal) = \sum_αS_2(\Gcal_α)$ is exact for the KCBS pentagon. We further show that in the spin-1 realization of the KCBS pentagon, a shared ms=0 eigenstate in each context forces $c_\MU = 1$, rendering every Maassen--Uffink-type bound trivial -- a structural mechanism that makes explicit why outcome-entropic uncertainty relations based on $c_\MU$ are silent on KCBS contextuality, while S2≈2.7266~bits throughout. Applied to KCBS and CHSH, the framework identifies regimes in which every state-dependent witness considered here is silent yet $S_2(\Gcal) > 0$ by an amount set by the projector geometry alone.
This volume is a computational and mathematical companion to the article "Information-Theoretic and Operational Measures of Quantum Contextuality". Rather than introducing new conceptual results, it provides complete derivations, independent cross-validations, and reproducible numerical implementations of every key result in the main article. Each quantity is established by two independent routes ---a direct matrix method using spin-1 operators, eigenvalue decompositions, and trace operations, and a geometric method based on the Majorana–Stellar representation on the Bloch–Poincaré sphere--- ensuring robustness against basis choices, degeneracies, and numerical artefacts. The treatment covers the KCBS geometry and observables, the mutual information energy, the operational contextuality measure D(G, ρ̂), the Majorana–Stellar formulation, and the associated uncertainty-optimization results, together with the accompanying Python reference implementation. It is intended for researchers and graduate students in quantum foundations, quantum information theory, and mathematical physics, assuming a working familiarity with finite-dimensional quantum mechanics. Published open access by Mersin University Press under a Creative Commons Attribution 4.0 International (CC BY 4.0) license.
Abstract We develop a geometric formulation of quantum contextuality organized around the overlap matrix T i j = d − 1 Tr [ ( P ^ i Q ^ j ) 2 ] in a d -dimensional Hilbert space, where P ^ i and Q ^ j are the joint-eigenspace projectors of two pairs of compatible observables sharing a common observable. The matrix T quantifies the information shared between these joint-eigenspaces. Rather than characterizing contextuality through outcome statistics alone, this formulation analyzes the geometric incompatibility encoded in T . Two distinct scalar contractions of T summarize this geometric content: the mutual information energy E = ∑ i j T i j , and the Maassen–Uffink parameter c MU , the largest amplitude overlap between vectors from the two joint eigenbases. We work with the logarithmic form S 2 = − log E (the subscript indicates Rényi order
Contextuality is a key distinguishing feature between classical and quantum physics. It expresses a fundamental obstruction to describing quantum theory using classical concepts. In turn, understood as a resource for quantum computation, it is expected to hold the key to quantum advantage. Yet, despite its long recognised importance in quantum foundations and, more recently, in quantum computation, the structural essence of contextuality has remained somewhat elusive - different frameworks address different aspects of the phenomenon, yet their precise relationship often remains unclear. This issue already looms large at the level of the Bell-Kochen-Specker theorem: while traditional proofs proceed by showing the nonexistence of valuations, the notion of state-independent contextuality in the marginal approach allows to prove contextuality from seemingly weaker assumptions. In the light of this, and at the absence of a unified mathematical framework for Kochen-Specker contextuality, the original algebraic approach has been widely abandoned, in favour of the study of contextual correlations. Here, we reinstate the algebraic perspective on contextuality. Concretely, by building on the novel concept of context connections, we reformulate the algebraic relations between observables originally postulated by Kochen and Specker, and we explicitly demonstrate their consistency with the notion of state-independent contextuality. In the present paper, we focus on the new conceptual ideas and discuss them in the concrete setting of spin-1 observables, specifically those in the example of [S. Yu and C.H. Oh, Phys. Rev. Lett., 108, 030402 (2012)]; in a companion paper, we generalise these ideas, obtain a complete characterisation of Kochen-Specker contextuality and provide a detailed comparison with the related notions of contextuality in the marginal and graph-theoretic approach.
In this paper we analyze the notion of measurement noncontextuality (MNC) and identify contextual scenarios which involve sequential measurements of only a single measurement device. We show that any noncontextual ontological model fails to explain the statistics of outcomes of a single carefully constructed positive-operator-valued measure (POVM) executed sequentially on a quantum system. The context of measurement arises from the different configurations in which the device can be used. We develop an inequality from the noncontextual (NC) ontic model, and construct a quantum situation involving measurements from the Klyachko-Can-Binicio\ifmmode \check{g}\else \v{g}\fi{}lu-Shumovsky (KCBS) inequality. We show that the resultant statistics arising from this device violate our NC inequality. This device can be generalized by incorporating measurements from arbitrary n-cycle contextuality inequalities of which n=5 corresponds to the KCBS inequality. We show that the NC and quantum bounds for various scenarios can be derived more easily using only the functional relationships between the outcomes for larger values n. This makes it one of the simpler contextual inequalities to analyze.
Quantum mechanics fundamentally challenges classical intuitions regarding reality and measurement, most notably through contextuality theorems such as Kochen-Specker and Bell-type inequalities. Traditional formulations treat measurement contexts as discrete sets of compatible observables or operational setups without a native, continuous geometric topology. In this paper, we introduce the framework of Quantum Measurement Context Curvature (QMCC), proposing that sequential, non-commutative measurements and environments naturally induce an irreducible geometric structure known as context curvature. By defining measurement contexts as ordered tuples C = (M_1, M_2, ..., M_n) and constructing non-commutative loops in context space, we quantify the path-dependence of quantum transition probabilities. We formalize the context curvature R_C as a sum over loops involving conditional probability discrepancies between alternative measurement orderings. This geometric perspective transcends standard operational descriptions, establishing a formal bridge between non-commutative algebraic structures of quantum mechanics and differential geometry, with potential applications in foundational quantum mechanics and advanced quantum information processing.