Adjust QuantumError.to_dict() to handle lack of Instruction.condition (#2301)

* Adjust QuantumError.to_dict() to handle lack of Instruction.condition

In Qiskit 2.0 the Instruction.condition attribute will be removed
following it's deprecation in 1.3.0. This attribute has been superseded
by the IfElseOp which covers the use case but offers more functionality.
The removal is pending in Qiskit/qiskit#13506 and the use of qiskit-aer
in Qiskit's tests is blocking progress on that PR. This commit makes the
usage of .condition optional to maintain compatibility with Qiskit<2.0
but also work in >=2.0 with the attribute removed.

* Handle condition for AerJump as a custom attribute

With the removal of .condition from the base instruction data model the
.c_if() method was also removed. To handle the conditional jump that
AerJump was used for a custom attribute .condition is added to the
instruction. This enables retaining the functionality, but doesn't rely
on the base data model to provide the attribute or method.

Author: mtreinish

qiskit_aer/library/control_flow_instructions/jump.py

@@ -29,6 +29,7 @@ class AerJump(Instruction):
     def __init__(self, jump_to, num_qubits, num_clbits=0):
         super().__init__("jump", num_qubits, num_clbits, [jump_to])
         self.condition_expr = None
+        self.condition = None
 
     def set_conditional(self, cond):
         """Set condition to perform this jump instruction.
@@ -42,5 +43,5 @@ def set_conditional(self, cond):
         if isinstance(cond, Expr):
             self.condition_expr = cond
         else:
-            self.c_if(*cond)
+            self.condition = cond
         return self

qiskit_aer/noise/errors/quantum_error.py

@@ -319,8 +319,9 @@ def to_dict(self):
                     inst_dict["params"] = inst.operation.params
                 if inst.operation.label:
                     inst_dict["label"] = inst.operation.label
-                if inst.operation.condition:
-                    inst_dict["condition"] = inst.operation.condition
+                condition = getattr(inst.operation, "condition", None)
+                if condition:
+                    inst_dict["condition"] = condition
                 circ_inst.append(inst_dict)
             instructions.append(circ_inst)
         # Construct error dict