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It is a simple 5 bit circuit, but it has 20,000 lines of QASM code. I try to put it in the composer, but the "Saving..." beside the file name will stay there for hours. I never saw its completion.
"Saving..." usually transition to "Saved" in a few seconds if the file has 100 lines of code.
Has anybody succeeded in running a large file? How long do you have to wait to see the "Saved"?
Indeed, the composer does not support such a deep circuit. While, the error is counterintuitive (I reported that to the the composer developers already) it kind of makes sense that you are unable to load a circuit with ~20K gates. The composer is useful for toy examples and to simulate the circuit "live" in the browser. As you noticed, simulating the situation you are describing is impractical.
More generally, the situation you are describing is not practical on real hardware neither. As explained, 20K gates is a lot for the current state of the art of quantum hardware.
In any case, I suggest you to use IBM Quantum Lab for non-toy situations.
Here is how to load a QASM file and run it in real hardware using the IBM Quantum Lab:
Upload your QASM file (long.qasm in my case) to the environment:
In the notebook (the default has many useful imports already), load the file:
circuit = QuantumCircuit.from_qasm_file('long.qasm') # Creates a circuit from the QASM file
sum(circuit.count_ops().values()) # Total amount of gates to be sure that's your big circuit
from qiskit.providers.ibmq import least_busy
least_busy_device = least_busy(provider.backends(
simulator=False, filters=lambda b: b.configuration().n_qubits >= 5))
job = execute(circuit, least_busy_device)
counts = job.result().get_counts() # This might take some time, since your job will be in the queue.
plot_histogram(counts)
