impiement the function create$\_$multi$\_$control$\_$U$($qc$,$ b$,$ r$,$ ancilla, control$\_$u$\_$gate$)$ with inputs:

$-$ qc : a handle to a QuantumCircuit

$-\backslash ($ b $\backslash )$ : a quantum register with $\backslash ($ n$=\backslash )$ len$($b$)$ control qubits

$-\backslash ($ r $\backslash )$ : a single result qubit

$-$ ancilla : a quantum register with $\backslash (\backslash$mathrm$\{$n$-1\}\backslash )$ ancillary qubits

$-$ control$\_$u$\_$gate : a reference to a function that when called as control$\_$u$\_$gate$($qc$,$ ctrl$\_$qubit, res$\_$qubit$)$ will implement the controlled$-$U gate with the specified control qubit operating on the result qubit.

Your circuit can use only the specified gates and must ensure that the ancillary qubits are all transformed back to $\backslash (|0\backslash$rangle $\backslash ).$

In $[]$:

$\backslash$# your code here

raise NotImplementedError

$```$

In $[]$: from numpy import pi

from qiskit import QuantumCircuit, QuantumRegister, execute

from qiskit.providers.aer import Aer

def control$\_$phase$\_$gate$($qc$,$ ctrl$,$ res$)$:

qc$.$cp$($pi$/2,$ ctrl$,$ res$)$

b $=$ QuantumRegister$(5,\text{'}$b$\text{'})$

r $=$ QuantumRegister$(1,\text{'}$r$\text{'})$

a $=$ QuantumRegister$(4,\text{'}$a$\text{'})$

qc $=$ QuantumCircuit$($ r$,$ b$,$ a$)$

qc$.$h$($b$)$

qc$.$h$($r$)$

create$\_$multi$\_$control$\_$U$($qc$,$ b$,$r$[0],$ a$,$ control$\_$phase$\_$gate $)$

$```$