Fix synth_mcmt_vchain for gates with parameters (Qiskit#13315)

* Fix mcmt-vchain with params * add reno * remove reno * add test that gates are 1q * add test for 1q gates
eliarbel · Oct 15, 2024 · fbfe738 · fbfe738
1 parent efdcb75
commit fbfe738
Show file tree

Hide file tree

Showing 3 changed files with 25 additions and 2 deletions.
diff --git a/crates/accelerate/src/synthesis/multi_controlled/mcmt.rs b/crates/accelerate/src/synthesis/multi_controlled/mcmt.rs
@@ -104,6 +104,7 @@ pub fn mcmt_v_chain(
     }
 
     let packed_controlled_gate = controlled_gate.operation;
+    let gate_params = controlled_gate.params;
     let num_qubits = if num_ctrl_qubits > 1 {
         2 * num_ctrl_qubits - 1 + num_target_qubits
     } else {
@@ -135,7 +136,7 @@ pub fn mcmt_v_chain(
     let targets = (0..num_target_qubits).map(|i| {
         Ok((
             packed_controlled_gate.clone(),
-            smallvec![] as SmallVec<[Param; 3]>,
+            gate_params.clone(),
             vec![Qubit::new(master_control), Qubit::new(num_ctrl_qubits + i)],
             vec![] as Vec<Clbit>,
         ))

diff --git a/qiskit/synthesis/multi_controlled/mcmt_vchain.py b/qiskit/synthesis/multi_controlled/mcmt_vchain.py
@@ -43,6 +43,9 @@ def synth_mcmt_vchain(
                   └───┘          └───┘
 
     """
+    if gate.num_qubits != 1:
+        raise ValueError("Only single qubit gates are supported as input.")
+
     circ = QuantumCircuit._from_circuit_data(
         mcmt_v_chain(gate.control(), num_ctrl_qubits, num_target_qubits, ctrl_state)
     )

diff --git a/test/python/circuit/library/test_mcmt.py b/test/python/circuit/library/test_mcmt.py
@@ -18,13 +18,14 @@
 
 from qiskit.exceptions import QiskitError
 from qiskit.compiler import transpile
-from qiskit.circuit import QuantumCircuit, QuantumRegister
+from qiskit.circuit import QuantumCircuit, QuantumRegister, Parameter
 from qiskit.circuit.library import (
     MCMT,
     MCMTVChain,
     CHGate,
     XGate,
     ZGate,
+    RYGate,
     CXGate,
     CZGate,
     MCMTGate,
@@ -264,6 +265,24 @@ def test_invalid_base_gate_width(self):
                 with self.assertRaises(ValueError):
                     _ = MCMTGate(gate, 10, 2)
 
+    def test_invalid_base_gate_width_synthfun(self):
+        """Test only 1-qubit base gates are accepted."""
+        for gate in [GlobalPhaseGate(0.2), SwapGate()]:
+            with self.subTest(gate=gate):
+                with self.assertRaises(ValueError):
+                    _ = synth_mcmt_vchain(gate, 10, 2)
+
+    def test_gate_with_parameters_vchain(self):
+        """Test a gate with parameters as base gate."""
+        theta = Parameter("th")
+        gate = RYGate(theta)
+        num_target = 3
+        circuit = synth_mcmt_vchain(gate, num_ctrl_qubits=10, num_target_qubits=num_target)
+
+        self.assertEqual(circuit.count_ops().get("cry", 0), num_target)
+        self.assertEqual(circuit.num_parameters, 1)
+        self.assertIs(circuit.parameters[0], theta)
+
 
 if __name__ == "__main__":
     unittest.main()