“…The connections used in our proof run through the real-time conversion of quantum circuits C to "phase polynomials" q C over Z K for K = 2 k , k ≥ 1 in [RC09,RCG18], which extended results by [DHH + 04] for k = 1, and the analysis of quadratic forms over Z 4 by Schmidt [Sch09] drawing on [Alb38,Bro72]. In the case of graph-state circuits and stabilizer circuits more generally, q C becomes a classical quadratic form over Z 4 , as treated also in [CGW18]. Our approach is related to ones involving Gauss sums [BvDR08, CCLL10, CGW18, Bk18] but exploits the availability of normal forms.…”