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point where the measurement happens simultaneously. This dataset can therefore
be seen as strong evidence against a problem introduced by the early measurement.
11.5.3 Microwave and Measurement Crosstalk
The most important step in the verification of the claim is the analysis of
known mechanisms that introduce artificial correlations into the result during the
measurement.
The experimental setup at hand is susceptible to two of these:
Microwave and measurment crosstalk.
Microwave crosstalk results from insufficient electrical isolation of the two
qubits that allows a microwave drive applied to one qubit to be seen by the other.
Earlier investigations have shown this microwave crosstalk to be suppressed by
about 20 dB, i.e. the second qubit sees about 1% of the drive applied to the first
qubit. Since, in this experiment, the qubits are placed off-resonance from each
other by at least 100 MHz, even these leaked microwaves are not able to have any
effect on the “wrong” qubit. Therefore, microwave crosstalk does not constitute
a problem for this experiment.
Measurement crosstalk, on the other hand, is still present despite the bandpass
filtering provided by the resonator coupling. Figure 11.5 shows the result of
experiments that quantify this crosstalk. In the experiment, a Rabi oscillation is
driven on one of the qubits to cause it to be alternatingly measured as | 1 〉 or | 0 〉.
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