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Figure 9.6: Capacitive Coupling Phase Calibration – a) Sequence: Both qubits
are hit with a π 2 -pulse (X π/2, Θ π/2 ) to generate the state | 00 〉 + | 10 〉 + e i θ | 01 〉 +
e i θ | 11 〉. The qubits are allowed to interact for a time t Delay before they are
measured (M). b) Time trace: An X-pulse on both qubits results in an eigenstate of
the coupling that simply decays, while a pulse of different phase on the two qubits
results in a state that will undergo a swap operation. This swap is maximized
at t Swap (dashed line). c) Phase trace: If t Delay is set to t Swap , the phase θ of
the pulse on the second qubit can be swept to find the phase offset between the
qubits. The point where the curves cross (dashed line) gives this offset. Which of
the crossings is the right one depends on the definition of the coordinate system
used in the Bloch sphere.
in Figure 9.4) for slightly different operating bias values for the qubit that was
initialized in the | 0 〉-state (here: Qubit B). The data will look like Figure 9.5b,
showing a maximized swap at the bias that places the qubits exactly on resonance.
If t Delay was not picked exactly right, the maximal swap in this dataset might be
less than the maximum achievable swap, but it should still give the right bias
calibration.
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