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Figure 8.10: T 1 – a) Bias sequence: The qubit is excited into the | 1 〉 state with
a π-pulse and measured after an increasing delay t Delay . b) T 1 : After the π-pulse,
the qubit decays exponentially from the | 1 〉 state back to the | 0 〉 state.
from Section 8.5. The 5% point used in the initial calibration of the measurement
pulse was chosen since, from experience (and from the math describing the
tunneling of the two states) the maximum visibility usually lies around the point
where the ground-state tunnels about 5% of the time. All parameters describing
the measure pulse can now be adjusted to maximize the visibility.
8.9 T 1
Now that we have a calibrated way to prepare the qubit in the excited state
and to measure its state as accurately as possible, we can start determining the
qubit’s intrinsic quality measures. The easiest quantity to measure is the qubit’s
energy relaxation time T 1 . To determine it, all one needs to do is prepare the qubit
in the excited state with a π-pulse and then measure its excited state population
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