Fix another typo

Author: albertomercurio

src/qobj/states.jl

@@ -37,7 +37,7 @@ function fock(N::Int, j::Int = 0; dims::Union{Int,AbstractVector{Int},Tuple} = N
     if getVal(sparse)
         array = sparsevec([j + 1], [1.0 + 0im], N)
     else
-        array = [i == j ? 1.0 + 0im : 0.0 + 0im for i in 1:N]
+        array = [i == (j+1) ? 1.0 + 0im : 0.0 + 0im for i in 1:N]
     end
     return QuantumObject(array; type = Ket, dims = dims)
 end