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I'm using qiskit for simulation. Suppose, I have 6 qubits with indices [0, 1, 2, 3, 4, 5] and I have an operator $U$ of size $4 \times 4$, such that it operates on 2 qubits.

How can we use qiskit to create a multi-control-multi-target gate such that, for example, the control qubit index is [1] and target qubit indices are [3, 4]? Or control indices are [0, 1] and target indices are [3, 4] or any other variation.

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We can create a quantum gate from any unitary operator $U$ using UnitaryGate class. And we can add any number of controls to any gate using control() method.

As an example, let's create a $4 \times 4$ unitary:

from qiskit.quantum_info import random_unitary

U = random_unitary(4)

Now, let's apply this operator to qubits $3$ and $4$ controlled by qubits $0$ and $1$.

from qiskit.circuit import QuantumCircuit
from qiskit.circuit.library import UnitaryGate

circ = QuantumCircuit(6)
circ.append(UnitaryGate(U).control(2), [0, 1, 3, 4])

The result:

enter image description here

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