Merge branch 'master' into clifford_simulator

.gitignore

@@ -134,6 +134,7 @@ dmypy.json
 
 # tmp files
 tmp/
+tmp.npy
 
 # Mac
 .DS_Store

src/qibo/gates/channels.py

@@ -179,6 +179,15 @@ def to_pauli_liouville(
 
         return super_op
 
+    def matrix(self, backend=None):
+        """"""
+        raise_error(
+            NotImplementedError,
+            "`matrix` method not defined for Channels. "
+            + "Please use one of the following methods: "
+            + "`to_choi` or `to_liouville` or `to_pauli_liouville`.",
+        )
+
 
 class KrausChannel(Channel):
     """General channel defined by arbitrary Kraus operators.

src/qibo/result.py

@@ -68,15 +68,16 @@ def state(self, numpy: bool = False):
         """State's tensor representation as a backend tensor.
 
         Args:
-            numpy (bool, optional): If ``True`` the returned tensor will be a numpy array,
+            numpy (bool, optional): If ``True`` the returned tensor will be a ``numpy`` array,
                 otherwise it will follow the backend tensor type.
                 Defaults to ``False``.
 
         Returns:
             The state in the computational basis.
         """
         if numpy:
-            return np.array(self._state)
+            return np.array(self._state.tolist())
+
         return self._state
 
     def probabilities(self, qubits: Optional[Union[list, set]] = None):

tests/test_gates_channels.py

@@ -45,6 +45,8 @@ def test_general_channel(backend):
     with pytest.raises(NotImplementedError):
         state = random_statevector(2**2, backend=backend)
         channel1.apply(backend, state, 2)
+    with pytest.raises(NotImplementedError):
+        channel1.matrix(backend)
 
 
 def test_controlled_by_channel_error():