Environment

• Qiskit version: 1.0.2
• Python version: 3.11.0
• Operating system: Linux

What is happening?

After a qasm2 round-trip, a XXPlusYYGate's to_matrix() method no longer works.

This problem seems somewhat special to XXPlusYYGate; it does not exist for most other two-qubit gates we have tried.

I've been able to reproduce this problem as well for CSGate, but not CXGate or CZGate.

How can we reproduce the issue?

from qiskit import qasm2, QuantumCircuit
from qiskit.circuit.library import XXPlusYYGate

# Build a circuit with a single XXPlusYYGate
qc = QuantumCircuit(2)
qc.append(XXPlusYYGate(0.1), [0, 1])

# Perform a qasm2 round trip
program = qasm2.dumps(qc)
qc2 = QuantumCircuit.from_qasm_str(program)

# Call to_matrix on original circuit instructions (works)
for inst in qc.data:
    inst.operation.to_matrix()

# Call to_matrix on circuit instructions after serialization (fails)
for inst in qc2.data:
    inst.operation.to_matrix()

throws the exception

File ~/serverless/.direnv/python-3.11.0/lib/python3.11/site-packages/qiskit/circuit/gate.py:63, in Gate.to_matrix(self)
     61 if hasattr(self, "__array__"):
     62     return self.__array__(dtype=complex)
---> 63 raise CircuitError(f"to_matrix not defined for this {type(self)}")

CircuitError: "to_matrix not defined for this <class 'qiskit.qasm2.parse._DefinedGate'>"

What should happen?

it should work the same as the circuit that did not undergo a round trip.

Any suggestions?

No response