pick[n] input-seq randomly pick n elements from each superposition in the input sequence if n is greater than the size of the superposition, then only return size(superposition) elements if n is less than or equal 0, return the empty ket
-- randomly pick three elements from the given superposition: pick[3] (|one> + |two> + |three> + |four> + |five> + |six> + |seven>) |three> + |seven> + |four>