def prep_gate(self, circuit, qreg, op):
        """
        Add state preparation gates to a circuit.

        Args:
            circuit (QuantumCircuit): circuit to add a preparation to.
            qreg (tuple(QuantumRegister,int)): quantum register to apply
            preparation to.
            op (tuple(str, int)): the basis label and index for the
            preparation op.
        """
        if self.prep_fun is None:
            pass
        else:
            self.prep_fun(circuit, qreg, op)
Add state preparation gates to a circuit.

        Args:
            circuit (QuantumCircuit): circuit to add a preparation to.
            qreg (tuple(QuantumRegister,int)): quantum register to apply
            preparation to.
            op (tuple(str, int)): the basis label and index for the
            preparation op.