Error Model on id gate, is not giving any error

Question

I am trying to play with NoiseModel of qiskit, and I noticed that error on id gate is not giving any error results, while error on the measurement (or other gates) does give an error:

def get_noise_model(p_err):
    error_gate1 = pauli_error([("X", p_err / 2), ("Z", p_err / 2), ("I", 1 - p_err)])
    noise_model = NoiseModel()
    noise_model.add_all_qubit_quantum_error(error_gate1, "id")
    print(error_gate1)
    return noise_model

qc = QuantumCircuit(2, 2)
qc.id(0)
qc.measure([0, 1], [0, 1])

results = (execute(qc,Aer.get_backend("aer_simulator"),noise_model=get_noise_model(0.2),shots=2048).result().get_counts())

plot_histogram(results)

Histogram:

And changing to :

noise_model.add_all_qubit_quantum_error(error_gate1, "measure")

gives that:

Why is that happening? If I perform noisy id gate

imports needed:

from qiskit.visualization import plot_histogram
from qiskit.providers.aer.noise import NoiseModel
from qiskit.providers.aer.noise.errors import pauli_error
from qiskit import QuantumCircuit, execute , Aer

Answer 1

By default execute function sets optimization_level value to $1$ which leads to some optimizations such as removing ID gates.

Just set optimization_level to $0$ to override this behavior:

results = (execute(qc,Aer.get_backend("aer_simulator"),noise_model=get_noise_model(0.2),optimization_level=0,shots=2048).result().get_counts())

The result should look like: