fix(#50): centralize duplicated default constants in utils.py

src/qc_compiler/__init__.py

@@ -21,6 +21,12 @@
 from qc_compiler.scheduling import CoherenceAwareScheduler, ScheduleResult
 from qc_compiler.transpiler import OptimizerConfig, QCompiler, QCompilerResult
 from qc_compiler.utils import (
+    DEFAULT_READOUT_ERROR,
+    DEFAULT_SINGLE_QUBIT_ERROR,
+    DEFAULT_SINGLE_QUBIT_GATE_TIME,
+    DEFAULT_T2_TIME,
+    DEFAULT_TWO_QUBIT_ERROR,
+    DEFAULT_TWO_QUBIT_GATE_TIME,
     TWO_QUBIT_GATES,
     compute_circuit_depth,
     compute_cnot_count,
@@ -30,6 +36,12 @@
 )
 
 __all__ = [
+    "DEFAULT_READOUT_ERROR",
+    "DEFAULT_SINGLE_QUBIT_ERROR",
+    "DEFAULT_SINGLE_QUBIT_GATE_TIME",
+    "DEFAULT_T2_TIME",
+    "DEFAULT_TWO_QUBIT_ERROR",
+    "DEFAULT_TWO_QUBIT_GATE_TIME",
     "TWO_QUBIT_GATES",
     "AdaptiveErrorMitigation",
     "AutoTuner",

src/qc_compiler/cost_model.py

@@ -18,6 +18,11 @@
 from qiskit import QuantumCircuit
 
 from qc_compiler.utils import (
+    DEFAULT_READOUT_ERROR,
+    DEFAULT_SINGLE_QUBIT_ERROR,
+    DEFAULT_SINGLE_QUBIT_GATE_TIME,
+    DEFAULT_T2_TIME,
+    DEFAULT_TWO_QUBIT_ERROR,
     TWO_QUBIT_GATES,
     compute_circuit_depth,
     get_backend_properties,
@@ -342,15 +347,15 @@ def _get_gate_fidelity_for_pair(
     def _avg_single_qubit_error(self) -> float:
         """Compute average single-qubit gate error across all qubits."""
         if not self.device.single_qubit_gate_errors:
-            return 0.0005
+            return DEFAULT_SINGLE_QUBIT_ERROR
 
         errors = list(self.device.single_qubit_gate_errors.values())
         return sum(errors) / len(errors)
 
     def _avg_two_qubit_error(self) -> float:
         """Compute average two-qubit gate error across all qubit pairs."""
         if not self.device.two_qubit_gate_errors:
-            return 0.01
+            return DEFAULT_TWO_QUBIT_ERROR
 
         errors = list(self.device.two_qubit_gate_errors.values())
         return sum(errors) / len(errors)
@@ -401,20 +406,17 @@ def _estimate_decoherence_error_default(
 
         Uses typical superconducting qubit T2 time of 150 μs.
         """
-        DEFAULT_T2 = 150e-6
-        DEFAULT_GATE_TIME = 50e-9
-
         depth = compute_circuit_depth(circuit)
-        total_time = depth * DEFAULT_GATE_TIME
-        fidelity = float(2.0 ** (-total_time / DEFAULT_T2))
+        total_time = depth * DEFAULT_SINGLE_QUBIT_GATE_TIME
+        fidelity = float(2.0 ** (-total_time / DEFAULT_T2_TIME))
         product = fidelity**circuit.num_qubits
 
         return 1.0 - product
 
     def _avg_gate_time(self) -> float:
         """Compute average gate duration across all gate types."""
         if not self.device.gate_lengths:
-            return 50e-9
+            return DEFAULT_SINGLE_QUBIT_GATE_TIME
 
         times = list(self.device.gate_lengths.values())
         return sum(times) / len(times)
@@ -435,7 +437,6 @@ def estimate_measurement_error(
         measured_qubits = self._get_measured_qubits(circuit)
 
         if not self.device.readout_errors:
-            DEFAULT_READOUT_ERROR = 0.015
             return 1.0 - (1.0 - DEFAULT_READOUT_ERROR) ** len(measured_qubits)
 
         product = 1.0

src/qc_compiler/cutting.py

@@ -43,7 +43,13 @@
 from qiskit import QuantumCircuit
 
 from qc_compiler.cost_model import CostModel
-from qc_compiler.utils import TWO_QUBIT_GATES
+from qc_compiler.utils import (
+    DEFAULT_SINGLE_QUBIT_ERROR,
+    DEFAULT_SINGLE_QUBIT_GATE_TIME,
+    DEFAULT_T2_TIME,
+    DEFAULT_TWO_QUBIT_ERROR,
+    TWO_QUBIT_GATES,
+)
 
 
 @dataclass
@@ -535,8 +541,8 @@ def _estimate_cut_error(
             depth = max(1, circuit.depth() // num_groups)
             avg_t2 = self._avg_t2()
             decoherence_error = 1 - float(
-                2.0 ** (-depth * 50e-9 / avg_t2)
-            ) if avg_t2 > 0 else 0.01
+                2.0 ** (-depth * DEFAULT_SINGLE_QUBIT_GATE_TIME / avg_t2)
+            ) if avg_t2 > 0 else DEFAULT_TWO_QUBIT_ERROR
 
             group_error = 1 - (1 - gate_error) * (1 - decoherence_error)
             group_errors.append(group_error)
@@ -654,7 +660,7 @@ def _avg_single_qubit_error(self) -> float:
                 self.cost_model.device.single_qubit_gate_errors.values()
             )
             return sum(errors) / len(errors)
-        return 0.0005
+        return DEFAULT_SINGLE_QUBIT_ERROR
 
     def _avg_two_qubit_error(self) -> float:
         """Get average two-qubit gate error from device or default."""
@@ -663,11 +669,11 @@ def _avg_two_qubit_error(self) -> float:
                 self.cost_model.device.two_qubit_gate_errors.values()
             )
             return sum(errors) / len(errors)
-        return 0.01
+        return DEFAULT_TWO_QUBIT_ERROR
 
     def _avg_t2(self) -> float:
         """Get average T2 time from device or default."""
         if self.cost_model.device.t2_times:
             times = list(self.cost_model.device.t2_times.values())
             return sum(times) / len(times)
-        return 150e-6
+        return DEFAULT_T2_TIME

src/qc_compiler/scheduling.py

@@ -33,6 +33,7 @@
 from qiskit import QuantumCircuit
 
 from qc_compiler.cost_model import CostModel
+from qc_compiler.utils import DEFAULT_SINGLE_QUBIT_GATE_TIME
 
 
 @dataclass
@@ -504,7 +505,7 @@ def _avg_gate_time(self) -> float:
         if self.cost_model.device.gate_lengths:
             times = list(self.cost_model.device.gate_lengths.values())
             return sum(times) / len(times)
-        return 50e-9
+        return DEFAULT_SINGLE_QUBIT_GATE_TIME
 
     def _compute_t2_priority(self, num_qubits: int) -> dict[int, float]:
         """Compute per-qubit T2-based scheduling priority.

src/qc_compiler/utils.py

@@ -13,6 +13,13 @@
 
 TWO_QUBIT_GATES = {"cx", "cz", "ecr", "swap", "rxx", "rzz", "ryy", "crx", "cry", "crz"}
 
+DEFAULT_SINGLE_QUBIT_ERROR = 0.0005
+DEFAULT_TWO_QUBIT_ERROR = 0.01
+DEFAULT_READOUT_ERROR = 0.015
+DEFAULT_T2_TIME = 150e-6
+DEFAULT_SINGLE_QUBIT_GATE_TIME = 50e-9
+DEFAULT_TWO_QUBIT_GATE_TIME = 300e-9
+
 
 def get_backend_properties(backend: BackendV2) -> dict:
     """Extract calibration properties from a quantum backend.
@@ -164,8 +171,8 @@ def get_avg_gate_time(device_props: dict, gate_type: str = "all") -> float:
 
     if not gate_lengths:
         if gate_type == "two":
-            return 300e-9
-        return 50e-9
+            return DEFAULT_TWO_QUBIT_GATE_TIME
+        return DEFAULT_SINGLE_QUBIT_GATE_TIME
 
     times = []
     for (gate_name, qubits), duration in gate_lengths.items():
@@ -174,7 +181,7 @@ def get_avg_gate_time(device_props: dict, gate_type: str = "all") -> float:
 
     if not times:
         if gate_type == "two":
-            return 300e-9
-        return 50e-9
+            return DEFAULT_TWO_QUBIT_GATE_TIME
+        return DEFAULT_SINGLE_QUBIT_GATE_TIME
 
     return sum(times) / len(times)