Implementing estimator interface

[doichanj]

What should we add?

Qiskit C++ currently only has sampler interface to run circuit to get sampling bitstrings. Estimator interface is also demanding to get estimation on Pauli strings.

Implementing a BackendEstimatorV2 class as well as BackendSamplerV2 class
(https://github.com/Qiskit/qiskit-cpp/blob/main/src/primitives/backend_sampler_v2.hpp)
and implementing estimator.run() function that will accept an EstimatorPub class as well as SamplerPub (https://github.com/Qiskit/qiskit-cpp/blob/main/src/primitives/containers/sampler_pub.hpp)
An EstimatorPub will have ISA circuit and observables (see https://quantum.cloud.ibm.com/docs/en/api/qiskit-ibm-runtime/estimator-v2)

estimator.run() function will return BackendEstimatorJob class as well as BackendSamplerJob class (https://github.com/Qiskit/qiskit-cpp/blob/main/src/primitives/backend_sampler_job.hpp) containing estimation values.

[added 9 June]
Using SparseObservable class for input pubs.

Implement Backend::run function that accepts std::vector<EstimatorPub> (at least for QRMI backend) to run as estimator program id.

[1ucian0]

❗ From June 3rd to 17th, this issue is participating in the 6th edition of unitaryHACK more info...

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Happy hacking!

[rosspeili]

Hey @doichanj opened a PR that addresses the issue, including ripple effects and complementary files, docs, code fixes that short the need for follow up PRs.

[jsaroni]

Hi @1ucian0, @doichanj,
Thank you for the check! I submitted the PR first complete with quickly passing test designs, did precision analyses from hardware runs that are often overlooked, and filing compliance that addressed the needed implementations. Please let me know if you have more feedback, I'm happy to discuss!

[Polarnova]

Opened a PR for #145.

[1ucian0]

Thank you to everyone who has submitted a PR for this issue! We currently have several promising fixes under review, so please hold off on submitting new PRs until the Qiskit team posts a follow-up comment here.

We will review the existing submissions in due course. Thank you for your patience!

[doichanj]

Thank you for submitting PR's for this PR but, I'm very sorry but I missed to add implementation guides in this issue.

I added two instructions:

• using SparseObservable class
• implement backend::run function for a vector of EstimatorPub to run with estimator program id on IQP

[doichanj]

I'm now reviewing #160 this PR well follows the instruction and work on the actual device