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esonator. The latter calibration is preferred as it simultaneously ensures that the
excitation indeed was swapped into the resonator rather than a two-level state.
For this, a second bias pulse is added to the sequence to sweep one of the other
qubits onto resonance with the resonator. The amplitude and length of this second
pulse can then be swept to maximize the excitation of the respective qubit. The
data looks like Figure 9.9b.
9.3.4 Timing Calibration
Due to the absence of measurement crosstalk, it is now no longer as straightforward
to calibrate the timing of the bias channels for the different qubits. Instead,
the coupling of the excitation through the resonator needs to be used. If the second
pulse on the receiving qubit is placed progressively earlier, it will eventually
happen before the excitation is fully swapped into the resonator. At this point,
the measured final amplitude will decrease as more and more of the excitation
remains in the resonator after the swap is over. Since the swaps take a finite time,
though, this reduction in the final amplitude happens gradually and might show
features resulting from complicated dynamics while both qubits are on resonance
with the resonator. Therefore, this method only gives a rough calibration of the
timing delay. If the final sequence only requires a single coupling operation in one
direction, though, it does not matter too much if the excitation remains in the
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