Quantum / CONCEPT

The inverse Gram matrix of an orthocross MIC is half-integral

For every dimension d and every orthonormal basis of C^d, the Gram matrix G of the orthocross MIC is invertible and every entry of G^(-1) is an integer or a half-integer. This proves the conjecture of J. B. DeBrota, C. A. Fuchs and B. C. Stacey (arXiv:1812.08762), who observed it numerically.