Combine RB and XEB to compute inferred errors

[NoureldinYosri]

This PR:

• Adds the option to specify the qubits to the XEB workflow
• Adds pauli error computation for 2q XEB
• Adds InferredXEBResult class which
  • computes inferred errors: pauli, XEB, and decay constant
  • has a convenience method to plot heatmap for each of the errors
  • has a convenience method to plot histogram of each of the erros.

[eliottrosenberg]

LGTM, but it would be good if we could add a few things, either in this PR or the next one.

Maybe we could have a single function that the user calls which runs both 2Q XEB and 1Q RB and returns a CombinedXEBRBResult. The CombinedXEBRBResult would then need methods for returning and visualizing the 1Q error rates too. For the histogram method, we could plot 1Q and 2Q errors on the same axes (maybe something like result.histogram(single_qubit=True, two_qubit=True)).

Thanks!

[NoureldinYosri]

@eliottrosenberg I added the ability to plot both single and two qubit pauli errors

---

The issue with a single function that runs both 2Q XEB and 1Q RB is the number of arguments which is not the best thing to have. That method will have 10+ arguments. alternatively I could group them into an RBOptions and XEBOptions classes, what do you think?

[codecov]

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[eliottrosenberg]

@eliottrosenberg I added the ability to plot both single and two qubit pauli errors

The issue with a single function that runs both 2Q XEB and 1Q RB is the number of arguments which is not the best thing to have. That method will have 10+ arguments. alternatively I could group them into an RBOptions and XEBOptions classes, what do you think?

I'm thinking that most of the parameters would be shared. It could be something like this:

Shared parameters:

• sampler
• qubits
• repetitions
• num_circuits
• random_state (seed for rng)

RB:

• num_clifford_range (call this depths_rb or something)

XEB:

• entangling gate
• cycle_depths (call this depths_xeb or something)

We can get rid of the use_xy_basis option for RB here, since we will always want that to be its default value, I think. So that's 8 parameters, and all of them will have default values except sampler, so it will be easy to use.

[NoureldinYosri]

@eliottrosenberg sg, I will add that method in a followup PR

[pavoljuhas]

LGTM with some minor suggestions.

[pavoljuhas]

LGTM with a final nit.