Define returns_state in capabilities

CHANGELOG.md

@@ -7,7 +7,7 @@
 ### Improvements
 
 * Improvement of the different `requirements.txt` and `requirements-ci.txt` files.
-[(#212)](https://github.com/PennyLaneAI/pennylane-qiskit/pull/212)
+  [(#212)](https://github.com/PennyLaneAI/pennylane-qiskit/pull/212)
 
 * The plugin now natively supports the adjoint of the `S`, `T`, and `SX` gates.
   [(#216)](https://github.com/PennyLaneAI/pennylane-qiskit/pull/216)
@@ -16,10 +16,14 @@
 
 * Use the centralized [Xanadu Sphinx Theme](https://github.com/XanaduAI/xanadu-sphinx-theme)
   to style the Sphinx documentation.
-[(#215)](https://github.com/PennyLaneAI/pennylane-qiskit/pull/215)
+  [(#215)](https://github.com/PennyLaneAI/pennylane-qiskit/pull/215)
 
 ### Bug fixes
 
+* Defines the missing `returns_state` entry of the
+  `capabilities` dictionary for devices.
+  [(#220)](https://github.com/PennyLaneAI/pennylane-qiskit/pull/220)
+
 ### Contributors
 
 This release contains contributions from (in alphabetical order):

pennylane_qiskit/qiskit_device.py

@@ -146,6 +146,7 @@ def __init__(self, wires, provider, backend, shots=1024, **kwargs):
         self.provider = provider
         self.backend_name = backend
         self._capabilities["backend"] = [b.name() for b in self.provider.backends()]
+        self._capabilities["returns_state"] = backend in self._state_backends
 
         # Check that the backend exists
         if backend not in self._capabilities["backend"]:

tests/test_integration.py

@@ -31,6 +31,7 @@ def test_load_device(self, d, backend):
         assert dev.shots == 1024
         assert dev.short_name == d[0]
         assert dev.provider == d[1]
+        assert dev.capabilities()["returns_state"] == (backend in state_backends)
 
     def test_incorrect_backend(self):
         """Test that exception is raised if name is incorrect"""