Move measurements after verbatim box (#187)

Author: speller26

qiskit_braket_provider/providers/adapter.py

@@ -29,10 +29,12 @@
 from qiskit.circuit import Measure, Parameter, ParameterExpression
 from qiskit.circuit.parametervector import ParameterVectorElement
 from qiskit.transpiler import Target
-from qiskit_ionq import ionq_gates
+from qiskit_ionq import add_equivalences, ionq_gates
 
 from qiskit_braket_provider.exception import QiskitBraketException
 
+add_equivalences()
+
 _GPHASE_GATE_NAME = "global_phase"
 
 _BRAKET_TO_QISKIT_NAMES = {
@@ -436,6 +438,7 @@ def to_braket(
     _validate_name_conflicts(circuit.parameters)
 
     # Handle qiskit to braket conversion
+    measured_qubits = set()
     for circuit_instruction in circuit.data:
         operation = circuit_instruction.operation
         gate_name = operation.name
@@ -445,7 +448,11 @@ def to_braket(
         if gate_name == "measure":
             qubit = qubits[0]  # qubit count = 1 for measure
             qubit_index = circuit.find_bit(qubit).index
-            braket_circuit.measure(qubit_index)
+            if qubit_index in measured_qubits:
+                raise ValueError(
+                    f"Cannot measure previously measured qubit {qubit_index}"
+                )
+            measured_qubits.add(qubit_index)
         elif gate_name == "barrier":
             warnings.warn(
                 "The Qiskit circuit contains barrier instructions that are ignored."
@@ -463,6 +470,10 @@ def to_braket(
 
             # Getting the index from the bit mapping
             qubit_indices = [circuit.find_bit(qubit).index for qubit in qubits]
+            if intersection := measured_qubits.intersection(qubit_indices):
+                raise ValueError(
+                    f"Cannot apply operation {gate_name} to measured qubits {intersection}"
+                )
             params = _create_free_parameters(operation)
             if gate_name in _QISKIT_CONTROLLED_GATE_NAMES_TO_BRAKET_GATES:
                 for gate in _QISKIT_CONTROLLED_GATE_NAMES_TO_BRAKET_GATES[gate_name](
@@ -492,10 +503,13 @@ def to_braket(
             )
 
     if verbatim:
-        return Circuit(braket_circuit.result_types).add_verbatim_box(
+        braket_circuit = Circuit(braket_circuit.result_types).add_verbatim_box(
             Circuit(braket_circuit.instructions)
         )
 
+    for qubit in sorted(measured_qubits):
+        braket_circuit.measure(qubit)
+
     return braket_circuit
 
 

qiskit_braket_provider/version.py

@@ -1,3 +1,3 @@
 """Qiskit-Braket provider version."""
 
-__version__ = "0.4.0"
+__version__ = "0.4.1"

tests/providers/test_adapter.py

@@ -323,6 +323,28 @@ def test_measure(self):
 
         self.assertEqual(braket_circuit, expected_braket_circuit)
 
+    def test_measure_repeated(self):
+        """Tests that repeated measurement on a qubit raises a ValueError."""
+        qiskit_circuit = QuantumCircuit(2, 2)
+        qiskit_circuit.h(0)
+        qiskit_circuit.cx(0, 1)
+        qiskit_circuit.measure(0, 0)
+        qiskit_circuit.measure([0, 1], [0, 1])
+
+        with self.assertRaises(ValueError):
+            to_braket(qiskit_circuit)
+
+    def test_gate_after_measure(self):
+        """Tests that adding a gate to a measured qubit raises a ValueError."""
+        qiskit_circuit = QuantumCircuit(2, 2)
+        qiskit_circuit.h(0)
+        qiskit_circuit.cx(0, 1)
+        qiskit_circuit.measure(0, 0)
+        qiskit_circuit.h(0)
+
+        with self.assertRaises(ValueError):
+            to_braket(qiskit_circuit)
+
     def test_reset(self):
         """Tests if NotImplementedError is raised for reset operation."""
 
@@ -436,13 +458,14 @@ def test_multiple_registers(self):
 
     def test_verbatim(self):
         """Tests that transpilation is skipped for verbatim circuits."""
-        qiskit_circuit = QuantumCircuit(2)
+        qiskit_circuit = QuantumCircuit(2, 1)
         qiskit_circuit.h(0)
         qiskit_circuit.cx(0, 1)
+        qiskit_circuit.measure(1, 0)
 
         assert to_braket(qiskit_circuit, {"x"}, True) == Circuit().add_verbatim_box(
             Circuit().h(0).cnot(0, 1)
-        )
+        ).measure(1)
 
     def test_parameter_vector(self):
         """Tests ParameterExpression translation."""