Stabilizer formalism: codespace = simultaneous +1 eigenspace of abelian subgroup S ⊂ P_n

Gottesman 1997 stabilizer formalism. The Pauli group P_n on n qubits has 4·4^n elements; an abelian subgroup S ⊂ P_n with n − k independent generators that does not contain −I defines a stabilizer code that encodes k logical qubits in n…