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Figure 11.4: Behavior of S: Examining the behavior of S versus sequence parameters
can verify a trustworthy implementation – a) S versus phase b, b ′ : As the
phase of the rotation pulses on the second qubit is varied, S shows the expected
sinusoidal response. b) S versus measurement delay: The fact that S shows only
the expected T 1 and T 2 decay, but no other features indicating a dependence on
the relative timing of the measurements, is strong evidence that the qubits are
truly decoupled during measurement.
the early measurement of one qubit might still prompt criticism as it opens the
locality loophole even wider by giving the qubits even more time to interact via the
unknown processes postulated by the loophole. To counter this criticism, it can be
shown that the relative timing of the measurement does not influence the resulting
S-value in a way that suggests the existence of an additional interaction allowed
by the time difference. Figure 11.4b shows the dependence of S on the delay of
the Bell rotations and measurement on the second qubit. As expected from the
additional qubit decoherence, S decreases as the measurement is delayed. But the
plot shows no features that correlate with the relative timing of the measurements
on the two qubits. Specifically, there is no reduction in S around t = −1 ns, the
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