The index

Quantum information

4 entries matching the current filters. Sorted by recently added.

Everyone expected additivity. Hastings produced a random counterexample, and the classical capacity of a quantum channel became genuinely hard.

Resolved in 2020 by a complexity-theoretic argument that nobody in operator algebras saw coming.

The answer is 7 when the dimension is a prime power. In dimension 6 nobody can get past 3.

Numerically found in every dimension tried, exactly constructed in many, and proved in none in general.