I have a custom gate in qiskit defined as follows:

sub_circuit = QuantumCircuit(3, name='toggle_cx')

toggle_cx = sub_circuit.to_instruction()

Say I add this to a QuantumCircuit:

qr = QuantumRegister(4)
new_qc = QuantumCircuit(qr)

new_qc.append(toggle_cx, [qr[1],qr[2],qr[3]])

Now, how do I get information about the qiskit-native gates that were used to make up this custom gate from the final QuantumCircuit object? I tried printing the QuantumCircuit object dictionary; it gave the following output:

{'_ancillas': [],
 '_base_name': 'circuit',
 '_calibrations': defaultdict(<class 'dict'>, {}),
 '_clbit_indices': {},
 '_clbits': [],
 '_control_flow_scopes': [],
 '_data': [(Instruction(name='toggle_cx', num_qubits=3, num_clbits=0, params=[]),
            [Qubit(QuantumRegister(4, 'q0'), 1),
             Qubit(QuantumRegister(4, 'q0'), 2),
             Qubit(QuantumRegister(4, 'q0'), 3)],
 '_global_phase': 0,
 '_layout': None,
 '_metadata': None,
 '_parameter_table': ParameterTable({}),
 '_parameters': [],
 '_qubit_indices': {Qubit(QuantumRegister(4, 'q0'), 2): BitLocations(index=2, registers=[(QuantumRegister(4, 'q0'), 2)]),
                    Qubit(QuantumRegister(4, 'q0'), 3): BitLocations(index=3, registers=[(QuantumRegister(4, 'q0'), 3)]),
                    Qubit(QuantumRegister(4, 'q0'), 1): BitLocations(index=1, registers=[(QuantumRegister(4, 'q0'), 1)]),
                    Qubit(QuantumRegister(4, 'q0'), 0): BitLocations(index=0, registers=[(QuantumRegister(4, 'q0'), 0)])},
 '_qubits': [Qubit(QuantumRegister(4, 'q0'), 0),
             Qubit(QuantumRegister(4, 'q0'), 1),
             Qubit(QuantumRegister(4, 'q0'), 2),
             Qubit(QuantumRegister(4, 'q0'), 3)],
 'cregs': [],
 'duration': None,
 'name': 'circuit-4',
 'qregs': [QuantumRegister(4, 'q0')],
 'unit': 'dt'}

In this output, it labels the corresponding instruction as toggle_cx and not the qiskit-native gates. I tried to use new_qc.decompose(), however, if my circuit had other gates like Hadamard or PauliX; it will decompose those gates too, into even more basic gates. I only want to see what gates is toggle_cx made up of.

Context: I'm trying to make custom qiskit backends, which will have access only to the QuantumCircuit object passed as a parameter.



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