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At this point, the squid ramp can be executed and the switching time t Switch
will indicate whether the qubit state remained in the operating branch during the
tunneling measurement (here: t Switch ≈ 12.4 µs) or whether it tunneled to the
neighboring branch (here: t Switch ≈ 16.2 µs). This completes the DC part of the
biasing sequence as shown in Figure 8.4a.
If the qubit’s ciritical current is too high and the qubit potential always has
many stable minima, i.e. three or more overlaps, the qubit can not be reset into
the operating branch as described above.
In that case, the qubit is reset by
alternatingly biasing it to the points where the operating branch is the left-most
or right-most stable branch. This will dynamically destabilize all branches other
than the operating branch and leads to a probability for finding the qubit in the
target branch that increases with the number of reset cycles. Usually 3 to 5 cycles
are sufficient to bring this probability to above 99.99%.
8.3 Step Edge
To maximize the non-linearity and thus the speed at which operations can be
performed on the qubit without driving unwanted transitions, it is desirable to
bias the qubit such that the operating minimum is as shallow as possible. We
call the point at which the qubit ground-state (| 0 〉) in the operating minimum
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