Add global barrier in qasm3 dump

qiskit/qasm3/ast.py

@@ -478,6 +478,15 @@ def __init__(self, indexIdentifierList: List[Identifier]):
         self.indexIdentifierList = indexIdentifierList
 
 
+class QuantumGlobalBarrier:
+    """
+    quantumBarrier
+        : 'barrier'
+    """
+
+    __slots__ = ()
+
+
 class QuantumReset(QuantumInstruction):
     """A built-in ``reset q0;`` statement."""
 

qiskit/qasm3/experimental.py

@@ -68,3 +68,7 @@ class ExperimentalFeatures(enum.Flag):
             }
         }
     """
+    GLOBAL_BARRIER = enum.auto()
+    """Support exporting using golobal barrier as proposed in
+        https://github.com/Qiskit/qiskit/issues/13485
+    """

qiskit/qasm3/exporter.py

@@ -975,8 +975,14 @@ def build_current_scope(self) -> List[ast.Statement]:
             if isinstance(instruction.operation, Gate):
                 nodes = [self.build_gate_call(instruction)]
             elif isinstance(instruction.operation, Barrier):
-                operands = [self._lookup_bit(operand) for operand in instruction.qubits]
-                nodes = [ast.QuantumBarrier(operands)]
+                if ExperimentalFeatures.GLOBAL_BARRIER in self.experimental and len(
+                    instruction.qubits
+                ) == len(self.scope.circuit.qubits):
+                    operands = [self._lookup_bit(operand) for operand in instruction.qubits]
+                    nodes = [ast.QuantumGlobalBarrier()]
+                else:
+                    operands = [self._lookup_bit(operand) for operand in instruction.qubits]
+                    nodes = [ast.QuantumBarrier(operands)]
             elif isinstance(instruction.operation, Measure):
                 measurement = ast.QuantumMeasurement(
                     [self._lookup_bit(operand) for operand in instruction.qubits]

qiskit/qasm3/printer.py

@@ -413,6 +413,9 @@ def _visit_QuantumBarrier(self, node: ast.QuantumBarrier) -> None:
         self._visit_sequence(node.indexIdentifierList, separator=", ")
         self._end_statement()
 
+    def _visit_QuantumGlobalBarrier(self, _node: ast.QuantumGlobalBarrier) -> None:
+        self._write_statement("barrier")
+
     def _visit_ProgramBlock(self, node: ast.ProgramBlock) -> None:
         self.stream.write("{\n")
         self._current_indent += 1

test/python/qasm3/test_export.py

@@ -2665,6 +2665,40 @@ def test_switch_v1_expr_target(self):
         test = dumps(qc, experimental=ExperimentalFeatures.SWITCH_CASE_V1)
         self.assertEqual(test, expected)
 
+    def test_global_barrier_all_qubits(self):
+        """Simple test that the global barrir is created"""
+        qc = QuantumCircuit(3)
+        qc.x(0)
+        qc.barrier()
+        qc.x(1)
+        expected = """\
+OPENQASM 3.0;
+include "stdgates.inc";
+qubit[3] q;
+x q[0];
+barrier;
+x q[1];
+"""
+        test = dumps(qc, experimental=ExperimentalFeatures.GLOBAL_BARRIER)
+        self.assertEqual(test, expected)
+
+    def test_global_barrier_partial_qubits(self):
+        """Simple test that the global barrir is created"""
+        qc = QuantumCircuit(3)
+        qc.x(0)
+        qc.barrier(0, 1)
+        qc.x(1)
+        expected = """\
+OPENQASM 3.0;
+include "stdgates.inc";
+qubit[3] q;
+x q[0];
+barrier q[0], q[1];
+x q[1];
+"""
+        test = dumps(qc, experimental=ExperimentalFeatures.GLOBAL_BARRIER)
+        self.assertEqual(test, expected)
+
 
 @ddt
 class TestQASM3ExporterFailurePaths(QiskitTestCase):