Quantum weight-enumerator A(x,y) and MacWilliams-Shor-Laflamme identity via quadratic form

Quantum weight enumerator polynomial and MacWilliams-Shor-Laflamme identity. Setup: for an [[n,k,d]] stabiliser code with projector Π, define the primary weight enumerator A_j = #{E ∈ G_n : wt(E) = j, E·Π = ±Π·E} counting Pauli errors of…