Lindblad model RWA bug fix

qiskit_dynamics/models/rotating_wave_approximation.py

@@ -232,7 +232,7 @@ def jax_transformable_func(t):
         )
 
         if return_signal_map:
-            signal_translator = lambda a, b: (get_rwa_signals(a), get_rwa_signals(b))
+            signal_translator = lambda a: (get_rwa_signals(a[0]), get_rwa_signals(a[1]))
             return rwa_model, signal_translator
         return rwa_model
 

qiskit_dynamics/solvers/solver_classes.py

@@ -190,7 +190,9 @@ def signals(self) -> SignalList:
         return self._signals
 
     @signals.setter
-    def signals(self, new_signals: Union[List[Signal], SignalList]):
+    def signals(
+        self, new_signals: Union[List[Signal], SignalList, Tuple[List[Signal]], Tuple[SignalList]]
+    ):
         """Set signals for the solver, and pass to the model."""
         self._signals = new_signals
         if self._rwa_signal_map is not None:

releasenotes/notes/lindblad-rwa-bug-491aaeed27ab4780.yaml

@@ -0,0 +1,9 @@
+---
+fixes:
+  - |
+    The ``rotating_wave_approximation`` function has been fixed in the case of
+    the ``model`` argument being a ``LindbladModel`` with ``return_signal_map=True``.
+    The returned signal mapping function was erroneously defined to take two inputs,
+    one for Hamiltonian signals and one for dissipator signals. This behaviour has been updated
+    to be consistent with the documentation, which states that in general this function accepts
+    only a single argument (in this case a tuple storing both sets of signals).

test/dynamics/models/test_rotating_wave_approximation.py

@@ -282,13 +282,13 @@ def test_signal_translator_lindblad_model(self):
             dissipator_signals=sigs,
         )
         f = rotating_wave_approximation(LM, 100, return_signal_map=True)[1]
-        rwa_ham_sig, rwa_dis_sig = f(sigs, sigs)
+        rwa_ham_sig, rwa_dis_sig = f((sigs, sigs))
         self.assertAllClose(rwa_ham_sig.complex_value(2)[:4], SignalList(sigs).complex_value(2))
         self.assertAllClose(rwa_dis_sig.complex_value(2)[:4], SignalList(sigs).complex_value(2))
         self.assertAllClose(rwa_ham_sig.complex_value(2)[4:], SignalList(s_prime).complex_value(2))
         self.assertAllClose(rwa_dis_sig.complex_value(2)[4:], SignalList(s_prime).complex_value(2))
 
-        self.assertTrue(f(None, None) == (None, None))
+        self.assertTrue(f((None, None)) == (None, None))
 
     def test_rwa_operators(self):
         """Tests get_rwa_operators using pseudorandom numbers."""