Check again that performing experiments in parallel does not significantly impact the results

[nelimee]

As this package is targeted towards 1-qubit state tomography, the idea of performing the different tomography experiments in parallel across the different qubits of a chip was raised.

As far as I remember, this has been checked successfully at the beginning of the sqt implementation. But there is no trace/documentation of it, and this check happened a few years ago.

In particular, it would be nice to have a complete script that could check that automatically. Here is how I see the process:

1. perform the parallel experiment, exactly what is done by default in sqt right now,
2. perform single-qubit experiment(s) (or multi-qubit experiments with non-adjacent qubits?),
3. post-process both experiments and check if the difference between the two results is within the sample-error or not.

There are two effects that might impact this experiment and prove the above assumption wrong:

1. cross-talk, i.e., error happening on nearby qubits when a quantum gate is applied. This type of error seems to be predominant when 2-qubit gates are used, but I did not see a lot of studies about potential cross-talk using single-qubit gates. Simultaneous single-qubit driving of semiconductor spin qubits at the fault-tolerant threshold might be an interesting read for this.
2. correlated measurements, that can be seen as a special case of cross-talk for measurements. Mitigating Coupling Map Constrained Correlated Measurement Errors on Quantum Devices might be interesting here.