Draft: Add support for Clifford+T target with NWQEC

pyproject.toml

@@ -18,6 +18,7 @@ classifiers = [
 ]
 dependencies = [
     "cirq-core>=1.4.1,<2.0.0",
+    "nwqec>=0.1.1",
     "ply>=3.11,<4.0.0",
     "pytket>=1.40.0,<3.0.0",
     "qbraid>=0.9.3,<1.0.0",

ucc/tests/test_compile.py

@@ -15,6 +15,11 @@
 from ucc import compile
 from ucc.transpilers.ucc_defaults import UCCDefault1
 from ucc.transpilers.aqc.mps_pass import MPSPass
+from ucc.transpilers.ucc_nwqec import (
+    CliffordTPass,
+    CliffordReduction,
+    is_clifford_or_t,
+)
 import numpy as np
 
 
@@ -644,3 +649,30 @@ def test_compiled_circuits_equivalent(circuit_function, num_qubits, seed):
     sv1 = Statevector(circuit)
     sv2 = Statevector(transpiled)
     assert sv1.equiv(sv2)
+
+
+def test_compile_clifford_t_pass():
+    circuit = qcnn_circuit(5, seed=42)
+    compiled_circuit = compile(circuit, custom_passes=[CliffordTPass()])
+
+    fidelity = np.abs(
+        np.vdot(Statevector(circuit).data, Statevector(compiled_circuit).data)
+    )
+
+    # Ensure fidelity is large, but not perfect since its approximate
+    assert np.abs(fidelity) > 0.95
+
+    for op in set(op.name for op in compiled_circuit):
+        assert is_clifford_or_t(op), f"Found non-Clifford+T gate: {op}"
+
+
+def test_compile_clifford_reduction_pass():
+    circuit = qcnn_circuit(5, seed=42)
+    compiled_circuit = compile(circuit, custom_passes=[CliffordReduction()])
+
+    fidelity = np.abs(
+        np.vdot(Statevector(circuit).data, Statevector(compiled_circuit).data)
+    )
+
+    # Ensure fidelity is large, but not perfect since its approximate
+    assert np.abs(fidelity) > 0.95

ucc/transpilers/ucc_nwqec.py

@@ -0,0 +1,103 @@
+import tempfile
+import nwqec
+import qiskit
+from qiskit.qasm2 import dump, loads
+from qiskit.qasm2 import LEGACY_CUSTOM_INSTRUCTIONS
+
+
+def is_clifford_or_t(gate_name: str) -> bool:
+    """Check if a gate is a Clifford or T gate using qiskit naming conventions."""
+    clifford_gates = {
+        "x",
+        "y",
+        "z",
+        "h",
+        "sx",
+        "sxdg",
+        "s",
+        "sdg",
+        "cx",
+        "cz",
+        "swap",
+        "id",
+    }
+    t_gates = {"t", "tdg"}
+    return gate_name in clifford_gates or gate_name in t_gates
+
+
+class CliffordTPass(qiskit.transpiler.basepasses.TransformationPass):
+    """
+    A transpiler pass that applies NWQEC's Clifford+T translation to a Qiskit DAGCircuit, lowering
+    the circuit to Clifford+T form.
+    """
+
+    def __init__(
+        self,
+        keep_ccx: bool = False,
+        epsilon: float | None = None,
+    ):
+        """
+        Args:
+            keep_ccx: preserve CCX gates when True.
+            epsilon: absolute error tolerance for RZ synthesis;
+                     defaults to abs(theta) * nwqec.DEFAULT_EPSILON_MULTIPLIER per angle.
+        """
+        super().__init__()
+        self._keep_ccx = keep_ccx
+        self._epsilon = epsilon
+
+    def run(self, dag):
+        circuit = qiskit.converters.dag_to_circuit(dag)
+
+        with tempfile.NamedTemporaryFile(suffix=".qasm") as tmp:
+            tmp_qasm = tmp.name
+            dump(circuit, tmp_qasm)
+            nwqec_circuit = nwqec.load_qasm(tmp_qasm)
+
+            nwqec_circuit = nwqec.to_clifford_t(
+                nwqec_circuit, epsilon=self._epsilon, keep_ccx=self._keep_ccx
+            )
+            return qiskit.converters.circuit_to_dag(
+                loads(
+                    nwqec_circuit.to_qasm(),
+                    custom_instructions=LEGACY_CUSTOM_INSTRUCTIONS,
+                )
+            )
+
+
+class CliffordReduction(qiskit.transpiler.basepasses.TransformationPass):
+    """
+    A transpiler pass that applies NWQEC's Clifford Reduction optimization to a Qiskit DAGCircuit.
+    Applies the Clifford reduction optimization (preserves parallelism while reducing non-T overhead).
+    Based on the technique from Wang et al. "Optimizing FTQC Programs through QEC Transpiler and Architecture Codesign" (2024).
+    """
+
+    def __init__(
+        self,
+        epsilon: float | None = None,
+    ):
+        """
+        Args:
+            epsilon: absolute error tolerance for RZ synthesis;
+                     defaults to abs(theta) * nwqec.DEFAULT_EPSILON_MULTIPLIER per angle.
+        """
+        super().__init__()
+        self._epsilon = epsilon
+
+    def run(self, dag):
+        circuit = qiskit.converters.dag_to_circuit(dag)
+
+        with tempfile.NamedTemporaryFile(suffix=".qasm") as tmp:
+            tmp_qasm = tmp.name
+            dump(circuit, tmp_qasm)
+            nwqec_circuit = nwqec.load_qasm(tmp_qasm)
+
+            nwqec_circuit = nwqec.to_clifford_reduction(
+                nwqec_circuit, epsilon=self._epsilon
+            )
+            return qiskit.converters.circuit_to_dag(
+                loads(
+                    nwqec_circuit.to_qasm(),
+                    custom_instructions=LEGACY_CUSTOM_INSTRUCTIONS,
+                )
+            )