diff --git a/mrmustard/lab_dev/circuit_components.py b/mrmustard/lab_dev/circuit_components.py
index cf5e8fa13..d6067f397 100644
--- a/mrmustard/lab_dev/circuit_components.py
+++ b/mrmustard/lab_dev/circuit_components.py
@@ -698,6 +698,8 @@ def _apply_btops_for_change_of_rep(self, indices: Sequence[int]) -> CircuitCompo
         ret = copy.deepcopy(self)
 
         for i in indices:
+            if len(self._index_representation[i]) > 2:
+                continue
             name, arg = self._index_representation[i]
 
             if name == "PS":
@@ -732,6 +734,8 @@ def _apply_btoq_for_change_of_rep(self, indices: Sequence[int]) -> CircuitCompon
 
         ret = copy.deepcopy(self)
         for i in indices:
+            if len(self._index_representation[i]) > 2:
+                continue
             name, arg = self._index_representation[i]
             if name == "Q":
                 ret._index_representation[i] = ("B", None)  # perhaps not needed -- can be removed
@@ -868,20 +872,20 @@ def __matmul__(self, other: CircuitComponent | Scalar) -> CircuitComponent:
         for m in other.wires.output.bra.modes:
             i = result.wires.index_dicts[0][m]
             j = other.wires.index_dicts[0][m]
-            result._index_representation[i] = other._index_representation[j]
+            result._index_representation[i] = other._index_representation[j][:2]
         for m in other.wires.output.ket.modes:
             i = result.wires.index_dicts[2][m]
             j = other.wires.index_dicts[2][m]
-            result._index_representation[i] = other._index_representation[j]
+            result._index_representation[i] = other._index_representation[j][:2]
 
         for m in self.wires.input.bra.modes:
             i = result.wires.index_dicts[1][m]
             j = self.wires.index_dicts[1][m]
-            result._index_representation[i] = self._index_representation[j]
+            result._index_representation[i] = self._index_representation[j][:2]
         for m in self.wires.input.ket.modes:
             i = result.wires.index_dicts[3][m]
             j = self.wires.index_dicts[3][m]
-            result._index_representation[i] = self._index_representation[j]
+            result._index_representation[i] = self._index_representation[j][:2]
 
         # now we check for indices that might have been contracted:
         idx_1, idx_2 = self.wires.contracted_indices(other.wires)
@@ -890,25 +894,29 @@ def __matmul__(self, other: CircuitComponent | Scalar) -> CircuitComponent:
             j = other.wires.index_dicts[1][m]
             if j not in idx_2:
                 i = result.wires.index_dicts[1][m]
-                result._index_representation[i] = other._index_representation[j]
+                result._index_representation[i] = other._index_representation[j][:2]
         for m in other.wires.input.ket.modes:
 
             j = other.wires.index_dicts[3][m]
             if j not in idx_2:
                 i = result.wires.index_dicts[3][m]
-                result._index_representation[i] = other._index_representation[j]
+                result._index_representation[i] = other._index_representation[j][:2]
 
         for m in self.wires.output.bra.modes:
             j = self.wires.index_dicts[0][m]
             if j not in idx_1:
                 i = result.wires.index_dicts[0][m]
-                result._index_representation[i] = self._index_representation[j]
+                result._index_representation[i] = self._index_representation[j][:2]
 
         for m in self.wires.output.ket.modes:
             j = self.wires.index_dicts[2][m]
             if j not in idx_1:
                 i = result.wires.index_dicts[2][m]
-                result._index_representation[i] = self._index_representation[j]
+                result._index_representation[i] = self._index_representation[j][:2]
+
+        if ((isinstance(self, BtoQ) or isinstance(self, BtoPS) )and (isinstance(other, BtoQ) or isinstance(other,BtoPS))):
+            for i in result.wires.indices:
+                result._index_representation[i] = result._index_representation[i] + (None,)
 
         return result