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• The energy difference between the ground and first excited state in the
operating minimum as a function of flux bias: Dividing this number by
will give the expected (angular) operating frequency of the qubit, i.e. the
frequency with which it needs to be driven to perform operations.
• The energy difference between the first and second excited levels in the
operating minimum: The frequency corresponding to this transition will
need to be significantly different from the operating frequency to allow for
operations on the qubit without exciting it into unwanted higher levels.
• The number of states in the right minimum: During measurement, the first
excited state in the operating minimum (here: left minimum) will be selectively
tunneled into the right minimum. There, it will end up in a level of
similar energy to the one it tunneled from, i.e. fairly high up in the minimum.
The rate at which the state will decay in the right minimum, and thus
the rate with which the measurement “latches” the outcome, is determined
by the number of the level that the state tunnels into. Higher states decay
faster with a rate of approximately T 1 /n, where n is the level number. Fast
decay is important to reduce the chance of the state tunneling back to the
left before latching.
For the calculation to yield trustable results, a few things need to be kept in mind:
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