Added the ctrl_state parameter to mcx() function (#12050)

* Added the ctrl_state parameter to mcx() function

* Fixing the Linting issue

* Fixed the Linting Issue

* Fixing Linting issue

* Added unit tests for mcx() func for ctrl_state param

* Fixed Linting Issue

* Added releasenotes for ctrl_state in mcx()

* Resolved Minor Changes

qiskit/circuit/quantumcircuit.py

@@ -4203,6 +4203,7 @@ class QuantumCircuit:
         target_qubit: QubitSpecifier,
         ancilla_qubits: QubitSpecifier | Sequence[QubitSpecifier] | None = None,
         mode: str = "noancilla",
+        ctrl_state: str | int | None = None,
     ) -> InstructionSet:
         """Apply :class:`~qiskit.circuit.library.MCXGate`.
 
@@ -4221,6 +4222,9 @@ class QuantumCircuit:
             target_qubit: The qubit(s) targeted by the gate.
             ancilla_qubits: The qubits used as the ancillae, if the mode requires them.
             mode: The choice of mode, explained further above.
+            ctrl_state:
+                The control state in decimal, or as a bitstring (e.g. '1').  Defaults to controlling
+                on the '1' state.
 
         Returns:
             A handle to the instructions created.
@@ -4234,14 +4238,16 @@ class QuantumCircuit:
         num_ctrl_qubits = len(control_qubits)
 
         available_implementations = {
-            "noancilla": MCXGrayCode(num_ctrl_qubits),
+            "noancilla": MCXGrayCode(num_ctrl_qubits, ctrl_state=ctrl_state),
-            "recursion": MCXRecursive(num_ctrl_qubits),
+            "recursion": MCXRecursive(num_ctrl_qubits, ctrl_state=ctrl_state),
-            "v-chain": MCXVChain(num_ctrl_qubits, False),
+            "v-chain": MCXVChain(num_ctrl_qubits, False, ctrl_state=ctrl_state),
-            "v-chain-dirty": MCXVChain(num_ctrl_qubits, dirty_ancillas=True),
+            "v-chain-dirty": MCXVChain(num_ctrl_qubits, dirty_ancillas=True, ctrl_state=ctrl_state),
             # outdated, previous names
-            "advanced": MCXRecursive(num_ctrl_qubits),
+            "advanced": MCXRecursive(num_ctrl_qubits, ctrl_state=ctrl_state),
-            "basic": MCXVChain(num_ctrl_qubits, dirty_ancillas=False),
+            "basic": MCXVChain(num_ctrl_qubits, dirty_ancillas=False, ctrl_state=ctrl_state),
-            "basic-dirty-ancilla": MCXVChain(num_ctrl_qubits, dirty_ancillas=True),
+            "basic-dirty-ancilla": MCXVChain(
+                num_ctrl_qubits, dirty_ancillas=True, ctrl_state=ctrl_state
+            ),
         }
 
         # check ancilla input

releasenotes/notes/added-parameter-ctrl_state-mcx-816dcd80e459a5ed.yaml

@@ -0,0 +1,18 @@
+---
+features:
+  - |
+    Added `ctrl_state` parameter to :func:`QuantumCircuit.mcx()`.
+
+
+    The :func:`QuantumCircuit.mcx()` function in the quantum circuit library has
+    been enhanced to include a `ctrl_state` parameter, allowing users to specify
+    the control state of the multi-controlled X gate. This parameter can accept
+    either a decimal value or a bitstring and defaults to controlling the '1'
+    state if not provided.
+
+    .. code-block:: python
+
+      from qiskit import QuantumCircuit
+      
+      qc = QuantumCircuit(3, 3)
+      qc.mcx([0, 1], 2, ctrl_state="00")

test/python/circuit/test_controlled_gate.py

@@ -970,6 +970,23 @@ class TestControlledGate(QiskitTestCase):
         ref_circuit.append(ccx, [qreg[0], qreg[1], qreg[2]])
         self.assertEqual(qc, ref_circuit)
 
+    @data((4, [0, 1, 2], 3, "010"), (4, [2, 1, 3], 0, 2))
+    @unpack
+    def test_multi_control_x_ctrl_state_parameter(
+        self, num_qubits, ctrl_qubits, target_qubit, ctrl_state
+    ):
+        """To check the consistency of parameters ctrl_state in MCX"""
+        qc = QuantumCircuit(num_qubits)
+        qc.mcx(ctrl_qubits, target_qubit, ctrl_state=ctrl_state)
+        operator_qc = Operator(qc)
+
+        qc1 = QuantumCircuit(num_qubits)
+        gate = MCXGate(num_ctrl_qubits=len(ctrl_qubits), ctrl_state=ctrl_state)
+        qc1.append(gate, ctrl_qubits + [target_qubit])
+        operator_qc1 = Operator(qc1)
+
+        self.assertEqual(operator_qc, operator_qc1)
+
     def test_open_control_composite_unrolling(self):
         """test unrolling of open control gates when gate is in basis"""
         # create composite gate