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arXiv:1206.3436 · Symmetry Integrability and Geometry Methods and Applications

'Magic' Configurations of Three-Qubit Observables and Geometric Hyperplanes of the Smallest Split Cayley Hexagon

Метод Санига

Published Nov 6, 2012• 4 citations
arXivHTMLPDF

Abstract

Recently Waegell and Aravind [J.Phys.A: Math.Theor.45 (2012), 405301, 13 pages] have given a number of distinct sets of three-qubit observables, each furnishing a proof of the Kochen-Specker theorem.Here it is demonstrated that two of these sets/configurations, namely the 18 2 -12 3 and 2 4 14 2 -4 3 6 4 ones, can uniquely be extended into geometric hyperplanes of the split Cayley hexagon of order two, namely into those of types V 22 (37; 0, 12, 15, 10) and V 4 (49; 0, 0, 21, 28) in the classification of Frohardt and Johnson [Comm.Algebra 22 (1994), 773-797].Moreover, employing an automorphism of order seven of the hexagon, six more replicas of either of the two configurations are obtained.

DOI
10.3842/sigma.2012.083

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Recently Waegell and Aravind [J.Phys.A: Math.Theor.45 (2012), 405301, 13 pages] have given a number of distinct sets of three-qubit observables, each furnishing a proof of the Kochen-Specker theorem.Here it is demonstrated that two of these sets/configurations, namely the 18 2 -12 3 and 2 4 14 2 -4 3 6 4 ones, can uniquely be extended into geometric hyperplanes of the split Cayley hexagon of order two, namely into those of types V 22 (37; 0, 12, 15, 10) and V 4 (49; 0, 0, 21, 28) in the classification of Frohardt and Johnson [Comm.Algebra 22 (1994), 773-797].Moreover, employing an automorphism of order seven of the hexagon, six more replicas of either of the two configurations are obtained.
Abstract. Disregarding the identity, the remaining 63 elements of the generalized three-qubit Pauli group are found to contain 12 096 distinct copies of Mermin’s magic pentagram. Remarkably, 12 096 is also the number of automorphisms of the smallest split Cayley hexagon. We give a few solid arguments showing that this may not be a mere coincidence. These arguments are mainly tied to the structure of certain types of geometric hyperplanes of the hexagon. It is further demonstrated that also an (182, 123)-type of magic configurations, recently proposed by Waegell and Aravind (J. Phys. A: Math. Theor. 45 (2012) 405301), seems to be intricately linked with automorphisms of the hexagon. Finally, the entanglement properties exhibited by edges of both pentagrams and these particular Waegell-Aravind configurations are addressed. PACS numbers: 03.65.Aa, 03.65.Fd, 03.65.Ud, 02.10.Ox 1.
A ``magic rectangle" of eleven observables of four qubits, employed by Harvey and Chryssanthacopoulos (2008) to prove the Bell-Kochen-Specker theorem in a 16-dimensional Hilbert space, is given a neat finite-geometrical reinterpretation in terms of the structure of the symplectic polar space W(7,2)W(7,2)W(7,2) of the real four-qubit Pauli group. Each of the four sets of observables of cardinality five represents an elliptic quadric in the three-dimensional projective space of order two (PG(3,2)(3,2)(3,2)) it spans, whereas the remaining set of cardinality four corresponds to an affine plane of order two. The four ambient PG(3,2)(3, 2)(3,2)s of the quadrics intersect pairwise in a line, the resulting six lines meeting in a point. Projecting the whole configuration from this distinguished point (observable) one gets another, complementary ``magic rectangle" of the same qualitative structure.
In this article, we show that sets of three-qubit quantum observables obtained by considering both the classical and skew embeddings of the split Cayley hexagon of order two into the binary symplectic polar space of rank three can be used to detect quantum state-independent contextuality. This reveals a fundamental connection between these two appealing structures and some fundamental tools in quantum mechanics and quantum computation. More precisely, we prove that the complement of a classically embedded hexagon does not provide a Mermin-Peres-like proof of the Kochen-Specker theorem whereas that of a skewly-embedded one does.
Split Cayley hexagons of order two are distinguished finite geometries living in the three-qubit symplectic polar space in two different forms, called classical and skew. Although neither of the two yields observable-based contextual configurations of their own, classically -embedded copies are found to fully encode contextuality properties of the most prominent three-qubit contextual configurations in the following sense: for each set of unsatisfiable contexts of such a contextual configuration there exists some classically-embedded hexagon sharing with the configuration exactly this set of contexts and nothing else. We demonstrate this fascinating property first on the configuration comprising all 315 contexts of the space and then on doilies, both types of quadrics as well as on complements of skew-embedded hexagons. In connection with the last-mentioned case and elliptic quadrics we also conducted some experimental tests on a Noisy Intermediate Scale Quantum (NISQ) computer to substantiate our theoretical findings.
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