In qiskit, doing 2 subsequent measurements of a Hadamard gate on the same qubit always gives 0 on the 2nd one

Question

When I execute the following circuit, I expect that in both classical registers, the content is identical.

q = QuantumRegister(1)
c = ClassicalRegister(2)
circuit = QuantumCircuit(q, c)
circuit.h(q[0])
circuit.measure(q[0], c[0])
circuit.measure(q[0], c[1])

backend = BasicAer.get_backend('qasm_simulator')
job = execute(circuit, backend, shots=100)
result = job.result()
counts = result.get_counts(circuit)

print(counts)

And the results are {'01': 44, '00': 56}, however I expect {'11': 44, '00': 56}

When I run the same circuit in the IBM Quantum Experience with the same simulator, I get the expected results.

What do I miss?

Answer 1

When I run your code on the most recent version of qiskit I get the expected results {'11': 55, '00': 45}. It could be the case therefore that you are running an older version of qiskit and this has been fixed recently. I would suggest updating your version using pip install --upgrade qiskit