Fix pauli.evolve dtype casting error (backport #8877)

qiskit/quantum_info/operators/symplectic/base_pauli.py

@@ -131,9 +131,9 @@ def compose(self, other, qargs=None, front=False, inplace=False):
         # Get phase shift
         phase = self._phase + other._phase
         if front:
-            phase += 2 * _count_y(x1, z2)
+            phase += 2 * _count_y(x1, z2, dtype=phase.dtype)
         else:
-            phase += 2 * _count_y(x2, z1)
+            phase += 2 * _count_y(x2, z1, dtype=phase.dtype)
 
         # Update Pauli
         x = np.logical_xor(x1, x2)
@@ -185,7 +185,7 @@ def conjugate(self):
     def transpose(self):
         """Return the transpose of each Pauli in the list."""
         # Transpose sets Y -> -Y. This has effect on changing the phase
-        parity_y = self._count_y() % 2
+        parity_y = self._count_y(dtype=self._phase.dtype) % 2
         if np.all(parity_y == 0):
             return self
         return BasePauli(self._z, self._x, np.mod(self._phase + 2 * parity_y, 4))
@@ -388,7 +388,8 @@ def _from_array(z, x, phase=0):
             raise QiskitError("z and x vectors are different size.")
 
         # Convert group phase convention to internal ZX-phase conversion.
-        base_phase = np.mod(_count_y(base_x, base_z) + phase, 4)
+        dtype = getattr(phase, "dtype", None)
+        base_phase = np.mod(_count_y(base_x, base_z, dtype=dtype) + phase, 4)
         return base_z, base_x, base_phase
 
     @staticmethod
@@ -601,23 +602,23 @@ def _evolve_h(base_pauli, qubit):
     z = base_pauli._z[:, qubit].copy()
     base_pauli._x[:, qubit] = z
     base_pauli._z[:, qubit] = x
-    base_pauli._phase += 2 * np.logical_and(x, z).T
+    base_pauli._phase += 2 * np.logical_and(x, z).T.astype(base_pauli._phase.dtype)
     return base_pauli
 
 
 def _evolve_s(base_pauli, qubit):
     """Update P -> S.P.Sdg"""
     x = base_pauli._x[:, qubit]
     base_pauli._z[:, qubit] ^= x
-    base_pauli._phase += x.T
+    base_pauli._phase += x.T.astype(base_pauli._phase.dtype)
     return base_pauli
 
 
 def _evolve_sdg(base_pauli, qubit):
     """Update P -> Sdg.P.S"""
     x = base_pauli._x[:, qubit]
     base_pauli._z[:, qubit] ^= x
-    base_pauli._phase -= x.T
+    base_pauli._phase -= x.T.astype(base_pauli._phase.dtype)
     return base_pauli
 
 
@@ -629,19 +630,21 @@ def _evolve_i(base_pauli, qubit):
 
 def _evolve_x(base_pauli, qubit):
     """Update P -> X.P.X"""
-    base_pauli._phase += 2 * base_pauli._z[:, qubit].T
+    base_pauli._phase += 2 * base_pauli._z[:, qubit].T.astype(base_pauli._phase.dtype)
     return base_pauli
 
 
 def _evolve_y(base_pauli, qubit):
     """Update P -> Y.P.Y"""
-    base_pauli._phase += 2 * base_pauli._x[:, qubit].T + 2 * base_pauli._z[:, qubit].T
+    xp = base_pauli._x[:, qubit].T.astype(base_pauli._phase.dtype)
+    zp = base_pauli._z[:, qubit].T.astype(base_pauli._phase.dtype)
+    base_pauli._phase += 2 * (xp + zp)
     return base_pauli
 
 
 def _evolve_z(base_pauli, qubit):
     """Update P -> Z.P.Z"""
-    base_pauli._phase += 2 * base_pauli._x[:, qubit].T
+    base_pauli._phase += 2 * base_pauli._x[:, qubit].T.astype(base_pauli._phase.dtype)
     return base_pauli
 
 
@@ -658,7 +661,7 @@ def _evolve_cz(base_pauli, q1, q2):
     x2 = base_pauli._x[:, q2].copy()
     base_pauli._z[:, q1] ^= x2
     base_pauli._z[:, q2] ^= x1
-    base_pauli._phase += 2 * np.logical_and(x1, x2).T
+    base_pauli._phase += 2 * np.logical_and(x1, x2).T.astype(base_pauli._phase.dtype)
     return base_pauli
 
 
@@ -670,7 +673,7 @@ def _evolve_cy(base_pauli, qctrl, qtrgt):
     base_pauli._x[:, qtrgt] ^= x1
     base_pauli._z[:, qtrgt] ^= x1
     base_pauli._z[:, qctrl] ^= np.logical_xor(x2, z2)
-    base_pauli._phase += x1 + 2 * np.logical_and(x1, x2).T
+    base_pauli._phase += x1 + 2 * np.logical_and(x1, x2).T.astype(base_pauli._phase.dtype)
     return base_pauli
 
 
@@ -687,7 +690,4 @@ def _evolve_swap(base_pauli, q1, q2):
 
 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])
-    return (x & z).sum(axis=axis, dtype=dtype)
+    return (x & z).sum(axis=1, dtype=dtype)

qiskit/quantum_info/operators/symplectic/pauli.py

@@ -286,12 +286,12 @@ def settings(self) -> Dict:
     def phase(self):
         """Return the group phase exponent for the Pauli."""
         # Convert internal ZX-phase convention of BasePauli to group phase
-        return np.mod(self._phase - self._count_y(), 4)[0]
+        return np.mod(self._phase - self._count_y(dtype=self._phase.dtype), 4)[0]
 
     @phase.setter
     def phase(self, value):
         # Convert group phase convention to internal ZX-phase convention
-        self._phase[:] = np.mod(value + self._count_y(), 4)
+        self._phase[:] = np.mod(value + self._count_y(dtype=self._phase.dtype), 4)
 
     @property
     def x(self):
@@ -639,7 +639,9 @@ def _from_scalar_op(cls, op):
             raise QiskitError(f"{op} is not an N-qubit identity")
         base_z = np.zeros((1, op.num_qubits), dtype=bool)
         base_x = np.zeros((1, op.num_qubits), dtype=bool)
-        base_phase = np.mod(cls._phase_from_complex(op.coeff) + _count_y(base_x, base_z), 4)
+        base_phase = np.mod(
+            cls._phase_from_complex(op.coeff) + _count_y(base_x, base_z), 4, dtype=int
+        )
         return base_z, base_x, base_phase
 
     @classmethod

qiskit/quantum_info/operators/symplectic/pauli_list.py

@@ -237,12 +237,12 @@ def equiv(self, other):
     def phase(self):
         """Return the phase exponent of the PauliList."""
         # Convert internal ZX-phase convention to group phase convention
-        return np.mod(self._phase - self._count_y(), 4)
+        return np.mod(self._phase - self._count_y(dtype=self._phase.dtype), 4)
 
     @phase.setter
     def phase(self, value):
         # Convert group phase convetion to internal ZX-phase convention
-        self._phase[:] = np.mod(value + self._count_y(), 4)
+        self._phase[:] = np.mod(value + self._count_y(dtype=self._phase.dtype), 4)
 
     @property
     def x(self):

releasenotes/notes/fix_8438-159e67ecb6765d08.yaml

@@ -0,0 +1,7 @@
+---
+fixes:
+  - |
+    Fixes issue where :meth:`~.Pauli.evolve` and `~.PauliList.evolve` would
+    raise a dtype error when evolving by certain Clifford gates which
+    modified the Pauli's phase.
+    Fixes `issue #8438 <https://github.com/Qiskit/qiskit-terra/issues/8438>`_

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

@@ -404,6 +404,34 @@ def test_evolve_clifford2(self, gate, label):
         self.assertEqual(value, value_h)
         self.assertEqual(value_inv, value_s)
 
+    @data(
+        *it.product(
+            (
+                IGate(),
+                XGate(),
+                YGate(),
+                ZGate(),
+                HGate(),
+                SGate(),
+                SdgGate(),
+                CXGate(),
+                CYGate(),
+                CZGate(),
+                SwapGate(),
+            ),
+            [int, np.int8, np.uint8, np.int16, np.uint16, np.int32, np.uint32, np.int64, np.uint64],
+        )
+    )
+    @unpack
+    def test_phase_dtype_evolve_clifford(self, gate, dtype):
+        """Test phase dtype for evolve method for Clifford gates."""
+        z = np.ones(gate.num_qubits, dtype=bool)
+        x = np.ones(gate.num_qubits, dtype=bool)
+        phase = (np.sum(z & x) % 4).astype(dtype)
+        paulis = Pauli((z, x, phase))
+        evo = paulis.evolve(gate)
+        self.assertEqual(evo.phase.dtype, dtype)
+
     def test_evolve_clifford_qargs(self):
         """Test evolve method for random Clifford"""
         cliff = random_clifford(3, seed=10)

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

@@ -2034,6 +2034,40 @@ def test_evolve_clifford2(self, gate):
         self.assertListEqual(value, value_h)
         self.assertListEqual(value_inv, value_s)
 
+    def test_phase_dtype_evolve_clifford(self):
+        """Test phase dtype during evolve method for Clifford gates."""
+        gates = (
+            IGate(),
+            XGate(),
+            YGate(),
+            ZGate(),
+            HGate(),
+            SGate(),
+            SdgGate(),
+            CXGate(),
+            CYGate(),
+            CZGate(),
+            SwapGate(),
+        )
+        dtypes = [
+            int,
+            np.int8,
+            np.uint8,
+            np.int16,
+            np.uint16,
+            np.int32,
+            np.uint32,
+            np.int64,
+            np.uint64,
+        ]
+        for gate, dtype in itertools.product(gates, dtypes):
+            z = np.ones(gate.num_qubits, dtype=bool)
+            x = np.ones(gate.num_qubits, dtype=bool)
+            phase = (np.sum(z & x) % 4).astype(dtype)
+            paulis = Pauli((z, x, phase))
+            evo = paulis.evolve(gate)
+            self.assertEqual(evo.phase.dtype, dtype)
+
     @combine(phase=(True, False))
     def test_evolve_clifford_qargs(self, phase):
         """Test evolve method for random Clifford"""