fix(#57): _get_gate_duration now uses device calibration data

src/qc_compiler/scheduling.py

@@ -481,9 +481,12 @@ def _get_gate_duration(
     ) -> int:
         """Get the duration of a gate in abstract time units.
 
-        Uses device calibration data when available. Falls back to
-        a simple model: single-qubit gates = 1 unit, two-qubit gates
-        = 3 units (reflecting typical duration ratios on IBM hardware).
+        Uses device calibration data when available. Looks up the
+        actual gate duration from gate_lengths and converts it to
+        abstract units relative to a single-qubit gate. Falls back
+        to a simple model: single-qubit gates = 1 unit, two-qubit
+        gates = 3 units (reflecting typical duration ratios on IBM
+        hardware).
 
         Args:
             gate_name: Name of the gate.
@@ -492,6 +495,26 @@ def _get_gate_duration(
         Returns:
             Duration in abstract time units.
         """
+        gate_lengths = self.cost_model.device.gate_lengths
+
+        if gate_lengths:
+            avg_sq_time = DEFAULT_SINGLE_QUBIT_GATE_TIME
+
+            sq_times = [
+                v for (g, qs), v in gate_lengths.items()
+                if len(qs) == 1
+            ]
+            if sq_times:
+                avg_sq_time = sum(sq_times) / len(sq_times)
+
+            key = (gate_name, tuple(qubits))
+            if key in gate_lengths:
+                return max(1, round(gate_lengths[key] / avg_sq_time))
+
+            for (g, qs), v in gate_lengths.items():
+                if g == gate_name and len(qs) == len(qubits):
+                    return max(1, round(v / avg_sq_time))
+
         if qubits and len(qubits) >= 2:
             return 3
         return 1

tests/test_scheduling.py

@@ -442,4 +442,52 @@ def test_alap_produces_different_schedule_than_asap(self, scheduler):
 
         assert asap_result.method == "asap"
         assert alap_result.method == "alap"
-        assert asap_result.method != alap_result.method
+        assert asap_result.method != alap_result.method
+
+
+class TestGateDurationCalibration:
+    """Regression tests for gate duration from device calibration (issue #57)."""
+
+    def test_gate_duration_uses_device_data(self):
+        from qc_compiler.cost_model import DeviceCharacterization
+
+        device = DeviceCharacterization(
+            backend_name="test",
+            num_qubits=2,
+            gate_lengths={
+                ("sx", (0,)): 50e-9,
+                ("sx", (1,)): 60e-9,
+                ("cx", (0, 1)): 300e-9,
+            },
+        )
+        model = CostModel()
+        model.device = device
+        scheduler = CoherenceAwareScheduler(cost_model=model)
+
+        assert scheduler._get_gate_duration("sx", [0]) == 1
+        assert scheduler._get_gate_duration("sx", [1]) == 1
+        assert scheduler._get_gate_duration("cx", [0, 1]) == 5
+
+    def test_gate_duration_fallback_without_device(self):
+        scheduler = CoherenceAwareScheduler(cost_model=CostModel())
+        assert scheduler._get_gate_duration("sx", [0]) == 1
+        assert scheduler._get_gate_duration("cx", [0, 1]) == 3
+
+    def test_gate_duration_matches_same_size_gate(self):
+        from qc_compiler.cost_model import DeviceCharacterization
+
+        device = DeviceCharacterization(
+            backend_name="test",
+            num_qubits=3,
+            gate_lengths={
+                ("sx", (0,)): 50e-9,
+                ("cx", (0, 1)): 250e-9,
+                ("cx", (1, 2)): 400e-9,
+            },
+        )
+        model = CostModel()
+        model.device = device
+        scheduler = CoherenceAwareScheduler(cost_model=model)
+
+        assert scheduler._get_gate_duration("cx", [0, 1]) == 5
+        assert scheduler._get_gate_duration("cx", [1, 2]) == 8