fixed issue 8438 PauliList.evolve raises exception

qiskit/quantum_info/operators/symplectic/base_pauli.py

@@ -689,5 +689,5 @@ def _count_y(x, z, dtype=None):
     """Count the number of I Pauli's"""
     axis = 1
     if dtype is None:
-        dtype = np.min_scalar_type(x.shape[axis])
+        dtype = np.int64(x.shape[axis])
     return (x & z).sum(axis=axis, dtype=dtype)

releasenotes/notes/fix_evolve_raises_exception_in_Cliffordcircuits-46453dfbef7ac2e2.yaml

@@ -0,0 +1,9 @@
+---
+fixes:
+  - |
+    Fixed an issue with the a bug in the BasePauli/Pauli classes where the phase vector is sometimes set as 
+    dtype uint8 instead of int64 leading to errors when calling the evolve function for circuits containing 
+    gates that modify the pauli phase vector.
+    The dtype of the phase vector should always be the same, so that evolution and other methods that attempt
+    to inplace modify the vector don't cause exceptions for mismatched dtypes.
+    Fixed #8438 <https://github.com/Qiskit/qiskit-terra/issues/8438>

test/python/quantum_info/operators/symplectic/test_pauli.py

@@ -434,6 +434,19 @@ def test_barrier_delay_sim(self):
         value = Pauli(circ)
         self.assertEqual(value, target)
 
+    def test_evolve_clifford_with_phase(self):
+        """Create circuit with gate that modifies Pauli phase"""
+        qc = QuantumCircuit(2)
+        qc.cz(0, 1)
+        op = Operator(qc)
+
+        pauli = random_pauli(2, seed=123)
+
+        value = Operator(pauli.evolve(qc))
+        target = op.adjoint().dot(pauli).dot(op)
+
+        self.assertEqual(value, target)
+
 
 if __name__ == "__main__":
     unittest.main()