review comments

qiskit_experiments/library/randomized_benchmarking/clifford_utils.py

@@ -38,7 +38,9 @@
 _CLIFFORD_INVERSE_2Q = np.load(f"{_DATA_FOLDER}/clifford_inverse_2q.npz")["table"]
 _clifford_compose_2q_data = np.load(f"{_DATA_FOLDER}/clifford_compose_2q_dense_selected.npz")
 _CLIFFORD_COMPOSE_2Q_DENSE = _clifford_compose_2q_data["table"]
+# valid indices for the columns of the _CLIFFORD_COMPOSE_2Q_DENSE table
 _valid_sparse_indices = _clifford_compose_2q_data["valid_sparse_indices"]
+# map a clifford number to the index of _CLIFFORD_COMPOSE_2Q_DENSE
 _clifford_num_to_dense_index = {idx: ii for ii, idx in enumerate(_valid_sparse_indices)}
 
 # Transpilation utilities

qiskit_experiments/library/randomized_benchmarking/data/generate_clifford_data.py

@@ -109,7 +109,27 @@ def gen_clifford_compose_2q_gate():
         for rhs in _CLIFF_SINGLE_GATE_MAP_2Q.values():
             composed = cliff_lhs.compose(_CLIFF_2Q[rhs])
             products[lhs, rhs] = _TO_INT_2Q[_hash_cliff(composed)]
-    return products.tocsr()
+    return products.tocsc()
+
+
+def gen_clifford_compose_2q_dense() -> tuple[np.typing.NDArray[int], list[int]]:
+    """Generate a dense multiplication table for 1-qubit Clifford numbers
+
+    The multiplication table is generated from the sparse table generated by :meth:`gen_clifford_compose_2q_gate`.
+
+    Returns:
+        Tuple with a dense multiplication table and the valid indices for the columns
+    """
+    _CLIFFORD_COMPOSE_2Q = gen_clifford_compose_2q_gate()
+    number_of_cliffords = _CLIFFORD_COMPOSE_2Q.shape[0]
+    valid_sparse_indices = [
+        num
+        for num in range(number_of_cliffords)
+        if _CLIFFORD_COMPOSE_2Q[:, num].nnz == number_of_cliffords - 1
+    ]
+    _CLIFFORD_COMPOSE_2Q_DENSE = _CLIFFORD_COMPOSE_2Q[:, valid_sparse_indices].toarray()
+
+    return _CLIFFORD_COMPOSE_2Q_DENSE, valid_sparse_indices
 
 
 _GATE_LIST_1Q = [
@@ -185,18 +205,10 @@ def gen_cliff_single_2q_gate_map():
         )
     np.savez_compressed("clifford_inverse_2q.npz", table=gen_clifford_inverse_2q())
 
-    _CLIFFORD_COMPOSE_2Q = gen_clifford_compose_2q_gate()
-    scipy.sparse.save_npz("clifford_compose_2q_sparse.npz", _CLIFFORD_COMPOSE_2Q)
-
-    _CLIFFORD_COMPOSE_2Q_TRANSPOSED = _CLIFFORD_COMPOSE_2Q.T
-    valid_sparse_indices = [
-        num for num in range(11520) if _CLIFFORD_COMPOSE_2Q_TRANSPOSED[num, :].nnz == 11520 - 1
-    ]
-    clifford_num_to_dense_index = {idx: ii for ii, idx in enumerate(valid_sparse_indices)}
+    _CLIFFORD_COMPOSE_2Q_DENSE, valid_sparse_indices = gen_clifford_compose_2q_dense()
 
     np.savez_compressed(
         "clifford_compose_2q_dense_selected.npz",
-        table=_CLIFFORD_COMPOSE_2Q[:, valid_sparse_indices].toarray(),
+        table=_CLIFFORD_COMPOSE_2Q_DENSE,
         valid_sparse_indices=valid_sparse_indices,
-        clifford_num_to_dense_index=clifford_num_to_dense_index,
     )

test/library/randomized_benchmarking/test_clifford_utils.py

@@ -204,7 +204,8 @@ def test_num_from_2q_circuit(self):
         qc.h(0)
         num = num_from_2q_circuit(qc)
         self.assertEqual(num, 5760)
-        qc = qc.decompose()
+        qc = QuantumCircuit(2)
+        qc.u(0, 0, np.pi, 0)
         with self.assertRaises(QiskitError):
             # raising an error is ok, num_from_2q_circuit does not support all 2-qubit gates
             num_from_2q_circuit(qc)