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the cosine forms a local minimum along one of the sidewalls of the parabola as
shown in Figure 2.4c rather than two equally sized ones in the center. This will
lead to quantum states that correspond to a very well quantified phase difference
across the tunnel junction. This type of qubit is therefore called “Phase Qubit”
[Martinis et al., 2002]. Historically the phase qubit has trailed behind the flux
and charge qubits in terms of the best reported energy relaxation times. But it
makes up for its lower T 1 with much higher visibility single-shot readout, ease of
coupling, and frequency tuneability. This makes it currently the best candidate
for implementing an experiment to violate Bell’s inequality in superconducting
circuits.
2.3 Superconducting Qubit Operation
2.3.1 Initialization
Due to the relatively short energy relaxation times, all three types of qubits
automatically initialize into their ground state once cooled to their operating
temperature.
Since the states in the phase qubit are localized in any one of possibly many
stable minima in the potential, the qubit must be biased with a proper sequence to
“guide” the relaxation into the desired minimum. This can be achieved either with
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