GQSP-Based Hamiltonian Simulation for the Hubbard-Holstein Model — Paper Implementation Challenge by achebiyam · Pull Request #1524 · Classiq/classiq-library

achebiyam · 2026-03-16T09:11:16Z

Paper Implementation Challenge Submission

GitHub Issue: #1504
Author: @achebiyam

Summary

First application of Generalized Quantum Signal Processing (GQSP) to an
electron-phonon coupled system (Hubbard-Holstein model) on the Classiq platform.

What's included

GQSP simulation verified on 5-qubit Hubbard-Holstein (overlap 0.9999999917)
Eigenbasis verification on full 8-qubit model (N_max=2, 41 Pauli terms)
Resource comparison: GQSP vs Suzuki-Trotter (orders 1, 2, 4) with depth and CX counts
Time-dependent physical observables (polaron dynamics, CDW order)
VQE comparison showing GQSP's advantage in systematic accuracy
Parameter regime study across coupling g, Hubbard U, phonon frequency ω
Documented Classiq LCU synthesis limitation at ≥16 Pauli terms

Primary reference

D. Motlagh and N. Wiebe, "Generalized Quantum Signal Processing",
PRX Quantum 5, 020368 (2024). arXiv:2308.01501

Notes

The notebook runs end-to-end on Google Colab with pip install "classiq[qsp]"
The .qmod file can be exported from the Classiq platform circuit link included in the notebook
The parameter sweep section uses analytical α estimates to avoid long Pauli decomposition runtimes

review-notebook-app · 2026-03-16T09:11:22Z

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github-actions · 2026-03-16T09:11:29Z

🔥 New notebook just dropped!

@amir-naveh , @TomerGoldfriend — come check out this shiny new addition to our repo.

achebiyam · 2026-03-16T09:44:30Z

Note: The .qmod export fails due to a serialization issue in lcu_pauli (TypeError: 'CParamScalar' object cannot be interpreted as an integer). This appears to be an SDK bug in write_qmod when used with lcu_pauli. The synthesized circuit is viewable on the Classiq platform here: https://platform.classiq.io/circuit/3B1F4EOqyt9Dqwju9Ik37lJQvc4

Happy to add the .qmod file once this serialization issue is resolved, or if the team can suggest a workaround.

TomerGoldfriend · 2026-03-17T09:24:28Z

Note: The .qmod export fails due to a serialization issue in lcu_pauli (TypeError: 'CParamScalar' object cannot be interpreted as an integer). This appears to be an SDK bug in write_qmod when used with lcu_pauli. The synthesized circuit is viewable on the Classiq platform here: https://platform.classiq.io/circuit/3B1F4EOqyt9Dqwju9Ik37lJQvc4

Happy to add the .qmod file once this serialization issue is resolved, or if the team can suggest a workaround.

Thank you @achebiyam , I will go over the PR. I will pass this bug to the team. There is no need to include .qmod anymore, so you can delete it and the write_qmod call.

achebiyam · 2026-03-17T17:23:58Z

Note: The .qmod export fails due to a serialization issue in lcu_pauli (TypeError: 'CParamScalar' object cannot be interpreted as an integer). This appears to be an SDK bug in write_qmod when used with lcu_pauli. The synthesized circuit is viewable on the Classiq platform here: https://platform.classiq.io/circuit/3B1F4EOqyt9Dqwju9Ik37lJQvc4
Happy to add the .qmod file once this serialization issue is resolved, or if the team can suggest a workaround.

Thank you @achebiyam , I will go over the PR. I will pass this bug to the team. There is no need to include .qmod anymore, so you can delete it and the write_qmod call.

Thanks @TomerGoldfriend! The submitted notebook already uses show(qprog_gqsp)
instead of write_qmod, so no changes needed on that front. Happy to address
any other feedback from your review.

orsa-classiq · 2026-03-25T15:48:36Z

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+{


Line #1. !pip install "classiq[qsp]" keyrings.alt pennylane -q
remove any pennylane use from the notebook

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orsa-classiq · 2026-03-25T15:48:36Z

@@ -0,0 +1,1243 @@
+{


Line #3. import keyring
remove all keyring related stuff from the notebook

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orsa-classiq · 2026-03-25T15:48:36Z

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+{


Line #2. classiq.authenticate()
remove authentication from the notebook. It is a pre assumption for the notebook

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…holstein_gqsp.ipynb

achebiyam · 2026-03-26T09:10:23Z

Done. I removed pennylane, keyring, and authenticate. Also removed the VQE section which depended on pennylane. Happy to address any further feedback.

orsa-classiq · 2026-03-29T07:17:40Z

@achebiyam
I'm sorry, it looks like almost the entire thing is generated by AI. Also the sectioning is weird and the explanations are not enough. If you want us to take a serious look at the notebook it needs a serious work from you. Take a look on other notebooks in the repo \ paper implementation project as an example.

achebiyam · 2026-03-29T23:49:51Z

I appreciate the feedback. This notebook represents several weeks of original research, including diagnosing a previously unreported platform limitation at exactly 16 Pauli terms and implementing the first GQSP simulation of an electron-phonon system on Classiq. I used AI tooling for polish and presentation, not for the research or implementation itself.

That said, I do understand the style doesn't match the existing notebooks in the repo. I'll rework the markdown and formatting to better align with your conventions and resubmit. Thanks again.

…holstein_gqsp.ipynb

Rework notebook style per reviewer feedback

achebiyam · 2026-04-20T01:09:38Z

Hi @orsa-classiq, @TomerGoldfriend, just checking in on this PR. I addressed all the feedback from late March (removed pennylane/keyring/authenticate, reworked the markdown style and tone to match the existing notebooks in the repo). Happy to make any additional changes if there's anything else you'd like adjusted. Thanks!

TomerGoldfriend · 2026-04-20T09:01:43Z

Hi @orsa-classiq, @TomerGoldfriend, just checking in on this PR. I addressed all the feedback from late March (removed pennylane/keyring/authenticate, reworked the markdown style and tone to match the existing notebooks in the repo). Happy to make any additional changes if there's anything else you'd like adjusted. Thanks!

OK @achebiyam, I will examine it. Sorry for missing your last commits and thanks for the reminder.

TomerGoldfriend · 2026-04-23T20:19:15Z

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+{


Line #23. GQSP_SCALE = 0.99
Can you explain this? it is typically to avoid numerical instabilities in gqsp_phases . I think you can try to increase it a bit. Anyway, please explain it.

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TomerGoldfriend · 2026-04-23T20:19:15Z

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+{


Please explain in more detail what is this model.
Currently, you have fraction of sentences, please write complete ones.
Explain (can be in one sentence) what is this model, does it have a physical meaning? and give a reference (to a paper or to wikipedia for example).
Many things are not defined here, what is b_i? what is c_{i\sigma}, and n_i? what is N_max?
Also, please specify explicitly which parameters you are going to set. Then, in the code, it will be good to set some hyperparameters clearly.

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TomerGoldfriend · 2026-04-23T20:19:15Z

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+{


For the Fermions, is it possible to work with Classiq's integration with OpenFermion?
You can define the Fermionic operators with openfermion FermionOperator and then use their jordan_wigner transform. Then you can use Classiq's built-in function which transforms QubitOperator to Classiq's SparsePauliOp .
See here for example: https://github.com/Classiq/classiq-library/blob/main/applications/chemistry/second_quantized_hamiltonian/second_quantized_hamiltonian.ipynb

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TomerGoldfriend · 2026-04-23T20:19:15Z

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+{


I did not understood this part, why is it needed?

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TomerGoldfriend

@achebiyam I left several comments.
Some additional general comments:

Please run the notebook, see that it is working, and leave the outputs. We should see the notebook execution cells outputs.
There is a lot of code with little explanations. You should add some concise explanations before very big code blocks, such that it will be clear what is implemented.

achebiyam added 2 commits March 16, 2026 02:04

Create README.md

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github-actions Bot added the new notebook label Mar 16, 2026

orsa-classiq reviewed Mar 25, 2026

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achebiyam added 3 commits March 26, 2026 02:03

Delete community/paper_implementations/hubbard_holstein_gqsp/hubbard_…

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…holstein_gqsp.ipynb

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Update README.md

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achebiyam added 2 commits March 31, 2026 20:19

Delete community/paper_implementations/hubbard_holstein_gqsp/hubbard_…

10e0feb

…holstein_gqsp.ipynb

Add files via upload

77058f9

Rework notebook style per reviewer feedback

TomerGoldfriend reviewed Apr 23, 2026

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TomerGoldfriend requested changes Apr 23, 2026

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Conversation

achebiyam commented Mar 16, 2026

Paper Implementation Challenge Submission

Summary

What's included

Primary reference

Notes

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