updating spin-chain-vqe tutorial to use SPSA

[nathanearnestnoble]

Work done by Aryaman Manish Kolhe (@Chasmiccoder) and Ritajit Majumdar (@ritajitmajumdar1). Would like to update tutorial with this SPSA implementation.

Fixes #3632

[review-notebook-app]

Check out this pull request on 

See visual diffs & provide feedback on Jupyter Notebooks.

---

Powered by ReviewNB

[qiskit-bot]

One or more of the following people are relevant to this code:

• @MeltemTolunay
• @miamico

[nathanearnestnoble]

Resolves issue 3632 (#3632)

[kaelynj]

Looks like this needs the title and metadata tags at the very top of the file. You should be able to replace this cell with the following:

---
title: Ground-state energy estimation of the Heisenberg chain with VQE
description: Build, deploy, and run a Qiskit pattern for simulating a Heisenberg chain and estimating its ground state energy.
---  

*Usage estimate: 37 minutes on a Heron processor (NOTE: This is an estimate only. Your runtime might vary.)*

Reply via ReviewNB

[kaelynj]

Suggested change

"description": "Build, deploy, and run a Qiskit pattern for simulating a Heisenberg chain and estimating its ground state energy.",

[kaelynj]

The title and metadata tags now need to go at the top of the file (though I'm not totally sure when that changed 😅 )

[kaelynj]

Suggested change

"title": "Ground state energy estimation of the Heisenberg chain with VQE"

[abbycross]

@kaelynj @nathanearnestnoble I fixed the metadata but am getting an error regarding an unused variable session, stemming from

    # Evaluate the problem using a QPU via Qiskit IBM Runtime
    with Session(backend=backend) as session:
        estimator = EstimatorV2()
        estimator.skip_transpilation = True
        x_opt = spsa(
            cost_func,
            x0=x0,
            args=(isa_ansatz, isa_observable, estimator, cost_history_dict),
            maxiter=maxiter,
        )

can you help clear the error? I can then clear the rest of the checks, like converting the output to images.

[Chasmiccoder]

Hi @abbycross and everyone. Thank you for helping merge this work.

I believe from the code snippet you have shared, the error can be fixed as follows:

with Session(backend=backend) as _:

The problem might be that if you write

with Session(backend=backend) as session:

then the variable session is being created but not used in the code block, which is being flagged by the compiler.

[ritajitmajumdar1]

Rather just do

estimator = EstimatorV2(mode=session)

This ensures the entire block runs as a single session. Unless the Estimator is initiated with session, I presume it would run in a job mode.

[abbycross]

Thanks!

[abbycross]

FYI - In my last commit I needed to revert the change that introduced the pip install for visualization - we intentionally no longer list it out because the exact syntax to install it varies depending on your OS (so instead we just point to the API docs).