fix(#61): replace circuit.find_bit(q).index with compatibility wrappers

src/qc_compiler/__init__.py

@@ -28,11 +28,13 @@
     DEFAULT_TWO_QUBIT_ERROR,
     DEFAULT_TWO_QUBIT_GATE_TIME,
     TWO_QUBIT_GATES,
+    clbit_index,
     compute_circuit_depth,
     compute_cnot_count,
     compute_idle_fraction,
     get_avg_gate_time,
     get_backend_properties,
+    qubit_index,
 )
 
 __all__ = [
@@ -63,9 +65,11 @@
     "QCompilerResult",
     "ScheduleResult",
     "TranspileConfig",
+    "clbit_index",
     "compute_circuit_depth",
     "compute_cnot_count",
     "compute_idle_fraction",
     "get_avg_gate_time",
     "get_backend_properties",
+    "qubit_index",
 ]

src/qc_compiler/batching.py

@@ -26,6 +26,7 @@
 from qiskit import QuantumCircuit
 
 from qc_compiler.cost_model import CostModel
+from qc_compiler.utils import qubit_index
 
 
 @dataclass
@@ -298,7 +299,7 @@ def _compute_core_hash(self, circuit: QuantumCircuit) -> int:
             gate_name = instr.operation.name
             if gate_name in ("measure", "barrier", "reset", "snapshot"):
                 continue
-            qubits = tuple(circuit.find_bit(q).index for q in instr.qubits)
+            qubits = tuple(qubit_index(circuit, q) for q in instr.qubits)
             params = tuple(
                 float(p) if hasattr(p, '__float__') else str(p)
                 for p in instr.operation.params
@@ -328,7 +329,7 @@ def _detect_measurement_basis(
             if instr.operation.name == "measure":
                 measure_indices.add(idx)
                 for q in instr.qubits:
-                    measured_qubits.add(circuit.find_bit(q).index)
+                    measured_qubits.add(qubit_index(circuit, q))
 
         if not measured_qubits:
             return "none"
@@ -347,7 +348,7 @@ def _detect_measurement_basis(
             if instr.operation.name in ("measure", "barrier", "reset", "snapshot"):
                 continue
             if len(instr.qubits) == 1:
-                qubit_idx = circuit.find_bit(instr.qubits[0]).index
+                qubit_idx = qubit_index(circuit, instr.qubits[0])
                 if qubit_idx in measured_qubits:
                     pre_measure_gates[qubit_idx].append(
                         instr.operation.name

src/qc_compiler/cost_model.py

@@ -26,6 +26,7 @@
     TWO_QUBIT_GATES,
     compute_circuit_depth,
     get_backend_properties,
+    qubit_index,
 )
 
 SINGLE_QUBIT_GATES = {"id", "rz", "sx", "x", "h", "s", "t", "p", "u", "u1", "u2", "u3"}
@@ -212,7 +213,7 @@ def estimate_gate_error(
             for instr in circuit.data:
                 gate_name = instr.operation.name
                 qubits = tuple(
-                    circuit.find_bit(q).index for q in instr.qubits
+                    qubit_index(circuit, q) for q in instr.qubits
                 )
                 if len(qubits) == 2 and gate_name in TWO_QUBIT_GATES:
                     fidelity = self._get_gate_fidelity_for_pair(
@@ -473,7 +474,7 @@ def _get_measured_qubits(self, circuit: QuantumCircuit) -> list[int]:
         for instr in circuit.data:
             if instr.operation.name == "measure":
                 for qubit in instr.qubits:
-                    measured.add(circuit.find_bit(qubit).index)
+                    measured.add(qubit_index(circuit, qubit))
         if not measured:
             return []
         return sorted(measured)

src/qc_compiler/cutting.py

@@ -49,6 +49,7 @@
     DEFAULT_T2_TIME,
     DEFAULT_TWO_QUBIT_ERROR,
     TWO_QUBIT_GATES,
+    qubit_index,
 )
 
 
@@ -367,7 +368,7 @@ def _find_cut_candidates(
         for idx, instr in enumerate(circuit.data):
             gate_name = instr.operation.name
             qubits = tuple(
-                circuit.find_bit(q).index for q in instr.qubits
+                qubit_index(circuit, q) for q in instr.qubits
             )
 
             if gate_name in TWO_QUBIT_GATES and len(qubits) == 2:
@@ -596,7 +597,7 @@ def union(x, y):
 
         for idx, instr in enumerate(circuit.data):
             qubits = tuple(
-                circuit.find_bit(q).index for q in instr.qubits
+                qubit_index(circuit, q) for q in instr.qubits
             )
             if len(qubits) == 2:
                 q0, q1 = qubits
@@ -638,7 +639,7 @@ def _extract_subcircuit(
 
         for idx, instr in enumerate(circuit.data):
             gate_qubits = tuple(
-                circuit.find_bit(q).index for q in instr.qubits
+                qubit_index(circuit, q) for q in instr.qubits
             )
 
             if idx in cut_gate_indices:

src/qc_compiler/fusion.py

@@ -37,6 +37,7 @@
 from qiskit.synthesis import OneQubitEulerDecomposer
 
 from qc_compiler.cost_model import CircuitMetrics, CostModel
+from qc_compiler.utils import qubit_index
 
 
 @dataclass
@@ -302,7 +303,7 @@ def _find_single_qubit_chains(
 
                 affected_qubits = set()
                 for q in instr.qubits:
-                    qidx = circuit.find_bit(q).index
+                    qidx = qubit_index(circuit, q)
                     affected_qubits.add(qidx)
                 for q in affected_qubits:
                     if q in active_chains:
@@ -314,7 +315,7 @@ def _find_single_qubit_chains(
                 continue
 
             if len(instr.qubits) == 1:
-                qubit_idx = circuit.find_bit(instr.qubits[0]).index
+                qubit_idx = qubit_index(circuit, instr.qubits[0])
 
                 if qubit_idx in active_chains:
                     active_chains[qubit_idx][2].append(idx)

src/qc_compiler/scheduling.py

@@ -33,7 +33,7 @@
 from qiskit import QuantumCircuit
 
 from qc_compiler.cost_model import CostModel
-from qc_compiler.utils import DEFAULT_SINGLE_QUBIT_GATE_TIME
+from qc_compiler.utils import DEFAULT_SINGLE_QUBIT_GATE_TIME, clbit_index, qubit_index
 
 
 @dataclass
@@ -214,14 +214,14 @@ def _asap_schedule(self, circuit: QuantumCircuit) -> QuantumCircuit:
 
         for instr in circuit.data:
             gate = instr.operation
-            qubits = [circuit.find_bit(q).index for q in instr.qubits]
+            qubits = [qubit_index(circuit, q) for q in instr.qubits]
 
             earliest_cycle = max(qubit_next_cycle[q] for q in qubits) if qubits else 0
 
             gate_duration = self._get_gate_duration(gate.name, qubits)
 
             target_qubits = [circuit.qubits[q] for q in qubits]
-            target_clbits = [circuit.find_bit(c).index for c in instr.clbits]
+            target_clbits = [clbit_index(circuit, c) for c in instr.clbits]
             clbit_refs = [scheduled.clbits[i] for i in target_clbits] if target_clbits else []
 
             scheduled.append(gate, target_qubits, clbit_refs)
@@ -271,7 +271,7 @@ def _alap_schedule(self, circuit: QuantumCircuit) -> QuantumCircuit:
 
         for i in range(len(circuit.data) - 1, -1, -1):
             instr = circuit.data[i]
-            qubits = [circuit.find_bit(q).index for q in instr.qubits]
+            qubits = [qubit_index(circuit, q) for q in instr.qubits]
 
             if not qubits:
                 gate_latest_start[i] = 0
@@ -299,9 +299,9 @@ def _alap_schedule(self, circuit: QuantumCircuit) -> QuantumCircuit:
         for i in gate_order:
             instr = circuit.data[i]
             gate = instr.operation
-            qubits = [circuit.find_bit(q).index for q in instr.qubits]
+            qubits = [qubit_index(circuit, q) for q in instr.qubits]
             target_qubits = [circuit.qubits[q] for q in qubits]
-            target_clbits = [circuit.find_bit(c).index for c in instr.clbits]
+            target_clbits = [clbit_index(circuit, c) for c in instr.clbits]
             clbit_refs = [scheduled.clbits[j] for j in target_clbits] if target_clbits else []
 
             scheduled.append(gate, target_qubits, clbit_refs)
@@ -351,23 +351,23 @@ def _coherence_aware_schedule(
 
         qubit_first_gate = [-1] * circuit.num_qubits
         for i, instr in enumerate(circuit.data):
-            qubits = [circuit.find_bit(q).index for q in instr.qubits]
+            qubits = [qubit_index(circuit, q) for q in instr.qubits]
             for q in qubits:
                 if qubit_first_gate[q] == -1:
                     qubit_first_gate[q] = i
 
         for i, instr in enumerate(circuit.data):
-            qubits = [circuit.find_bit(q).index for q in instr.qubits]
+            qubits = [qubit_index(circuit, q) for q in instr.qubits]
             for q in qubits:
                 if qubit_latest_gate[q] >= 0:
                     predecessors[i].add(qubit_latest_gate[q])
                 qubit_latest_gate[q] = i
 
         for i in range(num_gates - 1):
             if circuit.data[i].operation.name == "barrier":
-                for q in [circuit.find_bit(q).index for q in circuit.data[i].qubits]:
+                for q in [qubit_index(circuit, q) for q in circuit.data[i].qubits]:
                     for j in range(i + 1, num_gates):
-                        jqubits = [circuit.find_bit(q).index for q in circuit.data[j].qubits]
+                        jqubits = [qubit_index(circuit, q) for q in circuit.data[j].qubits]
                         if q in jqubits:
                             predecessors[j].add(i)
 
@@ -391,15 +391,15 @@ def _coherence_aware_schedule(
             if not ready:
                 break
 
-            ready.sort(key=lambda i: min(t2_priority.get(q, float('inf')) for q in [circuit.find_bit(q).index for q in circuit.data[i].qubits]) if circuit.data[i].qubits else float('inf'))
+            ready.sort(key=lambda i: min(t2_priority.get(q, float('inf')) for q in [qubit_index(circuit, q) for q in circuit.data[i].qubits]) if circuit.data[i].qubits else float('inf'))
 
             gate_idx = ready[0]
 
             instr = circuit.data[gate_idx]
             gate = instr.operation
-            qubits = [circuit.find_bit(q).index for q in instr.qubits]
+            qubits = [qubit_index(circuit, q) for q in instr.qubits]
             target_qubits = [circuit.qubits[q] for q in qubits]
-            target_clbits = [circuit.find_bit(c).index for c in instr.clbits]
+            target_clbits = [clbit_index(circuit, c) for c in instr.clbits]
             clbit_refs = [scheduled.clbits[j] for j in target_clbits] if target_clbits else []
 
             scheduled.append(gate, target_qubits, clbit_refs)
@@ -440,7 +440,7 @@ def _compute_idle_times(
         qubit_active_cycles = {q: 0 for q in range(circuit.num_qubits)}
         for instr in circuit.data:
             for qubit in instr.qubits:
-                qidx = circuit.find_bit(qubit).index
+                qidx = qubit_index(circuit, qubit)
                 qubit_active_cycles[qidx] += 1
 
         idle_times = {}
@@ -464,7 +464,7 @@ def _compute_asap_starts(self, circuit: QuantumCircuit) -> list[int]:
         starts = []
 
         for instr in circuit.data:
-            qubits = [circuit.find_bit(q).index for q in instr.qubits]
+            qubits = [qubit_index(circuit, q) for q in instr.qubits]
             if not qubits:
                 starts.append(0)
                 continue

src/qc_compiler/utils.py

@@ -21,6 +21,35 @@
 DEFAULT_TWO_QUBIT_GATE_TIME = 300e-9
 
 
+def qubit_index(circuit: QuantumCircuit, qubit) -> int:
+    """Get the integer index of a qubit in a circuit.
+
+    Uses circuit.find_bit() for compatibility, but can be updated
+    if Qiskit deprecates find_bit in a future release.
+
+    Args:
+        circuit: The quantum circuit.
+        qubit: A qubit reference from circuit.data.
+
+    Returns:
+        Integer index of the qubit.
+    """
+    return circuit.find_bit(qubit).index
+
+
+def clbit_index(circuit: QuantumCircuit, clbit) -> int:
+    """Get the integer index of a classical bit in a circuit.
+
+    Args:
+        circuit: The quantum circuit.
+        clbit: A classical bit reference from circuit.data.
+
+    Returns:
+        Integer index of the classical bit.
+    """
+    return circuit.find_bit(clbit).index
+
+
 def get_backend_properties(backend: BackendV2) -> dict:
     """Extract calibration properties from a quantum backend.