def qft_dag(self, qc, qregs):
        n = len(qregs)
        for i in reversed(range(n)):
            qc.h(qregs[i])
            for k in reversed(range(i)):
                try:
                    qc.cu1(-pi/(2**(i - k)), qregs[i], qregs[k])
                except:
                    continue