Fix registering global_phase parameters when creating CircuitData (…

…#13538) (#13541)

* fix registering global phase params

* add tests and reno

(cherry picked from commit 6f0a176)

Co-authored-by: Julien Gacon <jules.gacon@googlemail.com>

crates/accelerate/src/twirling.rs

@@ -267,7 +267,7 @@ fn generate_twirled_circuit(
     custom_gate_map: Option<&CustomGateTwirlingMap>,
     optimizer_target: Option<&Target>,
 ) -> PyResult<CircuitData> {
-    let mut out_circ = CircuitData::clone_empty_like(circ, None);
+    let mut out_circ = CircuitData::clone_empty_like(py, circ, None)?;
 
     for inst in circ.data() {
         if let Some(custom_gate_map) = custom_gate_map {

crates/circuit/src/circuit_data.rs

@@ -928,6 +928,7 @@ impl CircuitData {
             instruction_iter.size_hint().0,
             global_phase,
         )?;
+
         for item in instruction_iter {
             let (operation, params, qargs, cargs) = item?;
             let qubits = res.qargs_interner.insert_owned(qargs);
@@ -994,9 +995,13 @@ impl CircuitData {
             qubits,
             clbits,
             param_table: ParameterTable::new(),
-            global_phase,
+            global_phase: Param::Float(0.0),
         };
 
+        // use the global phase setter to ensure parameters are registered
+        // in the parameter table
+        res.set_global_phase(py, global_phase)?;
+
         for inst in instruction_iter {
             res.data.push(inst?);
             res.track_instruction_parameters(py, res.data.len() - 1)?;
@@ -1038,6 +1043,7 @@ impl CircuitData {
             instruction_iter.size_hint().0,
             global_phase,
         )?;
+
         let no_clbit_index = res.cargs_interner.get_default();
         for (operation, params, qargs) in instruction_iter {
             let qubits = res.qargs_interner.insert(&qargs);
@@ -1071,8 +1077,13 @@ impl CircuitData {
             qubits: BitData::new(py, "qubits".to_string()),
             clbits: BitData::new(py, "clbits".to_string()),
             param_table: ParameterTable::new(),
-            global_phase,
+            global_phase: Param::Float(0.0),
         };
+
+        // use the global phase setter to ensure parameters are registered
+        // in the parameter table
+        res.set_global_phase(py, global_phase)?;
+
         if num_qubits > 0 {
             let qubit_cls = QUBIT.get_bound(py);
             for _i in 0..num_qubits {
@@ -1526,16 +1537,18 @@ impl CircuitData {
     /// * capacity - The capacity for instructions to use in the output `CircuitData`
     ///     If `None` the length of `other` will be used, if `Some` the integer
     ///     value will be used as the capacity.
-    pub fn clone_empty_like(other: &Self, capacity: Option<usize>) -> Self {
-        CircuitData {
+    pub fn clone_empty_like(py: Python, other: &Self, capacity: Option<usize>) -> PyResult<Self> {
+        let mut empty = CircuitData {
             data: Vec::with_capacity(capacity.unwrap_or(other.data.len())),
             qargs_interner: other.qargs_interner.clone(),
             cargs_interner: other.cargs_interner.clone(),
             qubits: other.qubits.clone(),
             clbits: other.clbits.clone(),
             param_table: ParameterTable::new(),
-            global_phase: other.global_phase.clone(),
-        }
+            global_phase: Param::Float(0.0),
+        };
+        empty.set_global_phase(py, other.global_phase.clone())?;
+        Ok(empty)
     }
 
     /// Append a PackedInstruction to the circuit data.

releasenotes/notes/fix-global-phase-assign-d05f182ed9ddcf57.yaml

@@ -0,0 +1,14 @@
+---
+fixes:
+  - |
+    Fixed a series of bugs when processing circuit with parameterized global phases,
+    where upon assignment the global phase was not correctly assigned.
+    Known cases this affected include:
+
+    * assigning parameters after calling :meth:`.QuantumCircuit.decompose` on a circuit, 
+      where the decomposition introduces a global phase
+    * assigning parameters on a circuit constructed from a DAG via :func:`.dag_to_circuit`
+    * assigning parameters on circuits created with :func:`.pauli_twirl_2q_gates`, where 
+      the circuit to be twirled had a parameterized global phase
+
+    Fixed `#13534 <https://github.com/Qiskit/qiskit/issues/13534>`__.

test/python/circuit/test_parameters.py

@@ -1246,6 +1246,18 @@ def test_repeated_gates_to_dag_and_back(self):
         bound_test_qc = test_qc.assign_parameters({theta: 1})
         self.assertEqual(len(bound_test_qc.parameters), 0)
 
+    def test_global_phase_to_dag_and_back(self):
+        """Test global phase parameters are correctly handled to dag and back."""
+        from qiskit.converters import circuit_to_dag, dag_to_circuit
+
+        theta = Parameter("theta")
+        qc = QuantumCircuit(global_phase=theta)
+
+        test_qc = dag_to_circuit(circuit_to_dag(qc))
+
+        bound_test_qc = test_qc.assign_parameters({theta: 1})
+        self.assertEqual(bound_test_qc.global_phase, 1)
+
     def test_rebinding_instruction_copy(self):
         """Test rebinding a copied instruction does not modify the original."""
 
@@ -1617,6 +1629,22 @@ def test_sub_allow_unknown_parameters(self):
         subbed = x.subs({y: z}, allow_unknown_parameters=True)
         self.assertEqual(subbed, x)
 
+    def test_decompose_with_global_phase(self):
+        """Test decomposing a circuit which introduces a global phase is correctly bound.
+
+        Regression test of #13534.
+        """
+        x = Parameter("x")
+        qc = QuantumCircuit(1)
+        qc.rz(x, 0)
+
+        bound = qc.decompose().assign_parameters([1])
+
+        expect = QuantumCircuit(1)
+        expect.rz(1, 0)
+
+        self.assertEqual(expect.decompose(), bound)
+
 
 def _construct_circuit(param, qr):
     qc = QuantumCircuit(qr)

test/python/circuit/test_twirling.py

@@ -15,7 +15,7 @@
 import ddt
 import numpy as np
 
-from qiskit.circuit import QuantumCircuit, pauli_twirl_2q_gates, Gate
+from qiskit.circuit import QuantumCircuit, pauli_twirl_2q_gates, Gate, Parameter
 from qiskit.circuit.library import (
     CXGate,
     ECRGate,
@@ -210,3 +210,13 @@ def test_error_on_parameterized_gate(self):
         qc = QuantumCircuit(5)
         with self.assertRaises(QiskitError):
             pauli_twirl_2q_gates(qc, [RZXGate(3.24)])
+
+    def test_with_global_phase(self):
+        """Test twirling a circuit with parameterized global phase."""
+
+        x = Parameter("x")
+        qc = QuantumCircuit(2, global_phase=x)
+        res = pauli_twirl_2q_gates(qc, seed=2)
+        bound = res.assign_parameters([1])
+
+        self.assertEqual(bound.global_phase, 1)