I have a 2 qubits system, maximally entangled, and I performed measurement on one of the qubit.

q = QuantumRegister(2)
c = ClassicalRegister(1)
qc = QuantumCircuit(q, c)
###create Bell State Qubit########
### Perform Measurement ##########
job = execute(qc,simulator,shots = 1000)
result = job.result()
counts = result.get_counts(qc)
print("\nTotal count for 0 and 1 are:",counts)

Before measurement, the state of the 2 qubit is $|00\rangle+|11\rangle/\sqrt{2}$. After obtaining the measurement result, I measured another qubit. I expected the 2nd qubit to collapse to either 1 of the 2 states($|0\rangle$ or $|1\rangle$) after measurement, but the result shows it is still in the superposition state. How do I renormalise the qubit state after measurement?

job = execute(qc,simulator,shots=1000)
result = job.result()
counts = result.get_counts(qc)
print("\n Total count for 0 and 1 are:,counts")

1 Answer 1


It looks like you are using the simulator, so adding a reset on the qubit you want to renormalize would work. The reset operation sets a qubit back to the ground state, $|0\rangle$. You would call this like any other operation: circuit.reset(<qubits>). Note: This will not work on the real devices.

If you think it is still in superposition after the measurement, applying another H-Gate would fix that as well.

However, if you plan to continue using the simulator, applying the reset might be the better option as you will always be sure, no matter what, that that qubit is back in the $|0\rangle$ state.


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