Implement QFT Section IV.1 simulation by Tatgithub02 · Pull Request #1692 · Classiq/classiq-library

Tatgithub02 · 2026-07-31T17:49:33Z

Issue

Closes #580

What This Does

Implements the QFT simulation from Section IV.1 of the paper
Simulating Quantum Field Theories on Gate-Based Quantum Computers
by Gayathree M. Vinod and Anil Shaji.

Reproduces Fig. 2 — the oscillatory dynamics of a fermion transitioning
into a fermion-plus-boson pair in a 1+1D Yukawa theory on a 12-qubit register.

Implementation Details

Physics Setup:

12 qubits: 3 fermionic modes (Jordan–Wigner), 3 antifermion modes (JW), 3 bosonic modes (2 qubits each)
Hamiltonian: 2257 Pauli strings
Initial state: |f⟩₂ (K=2, Q=1); Tracked state: |f⟩₁⊗|φ⟩₁ (K=2, Q=1)

Simulations:

Exact evolution — SciPy expm_multiply (reference)
Gate-based — Classiq Suzuki–Trotter (order=1, repetitions=10)

Results

✓ Exact evolution reproduces paper Fig. 2:

Peak population: 0.2249 (paper reports ~0.225)
Period: 0.131 m_π⁻¹
P(t=0.2): 0.2238

✓ Closed-form Rabi validation:

Max deviation from exact: 4×10⁻¹⁴ (two-level system is exact)

✓ Conservation laws verified:

[H, K] = 0 (momentum conserved)
[H, Q] = 0 (charge conserved)

✓ Gate-based Trotter simulation:

Circuit: 12 qubits, ~54k gates, ~19k CNOTs
Matches exact within validated window (t ≤ 0.2)

Files Included

qft_simulation.ipynb (46 cells, ~15–20 min runtime)
qft_simulation.qmod (~1.2 MB, compiled model)

Testing

pip install "classiq==1.19.1" numpy scipy matplotlib
jupyter notebook qft_simulation.ipynb
# Kernel → Restart & Run All

Checklist

Notebook runs with classiq==1.19.1
Files in research/qft_simulation/
File names unique and descriptive
Required files included: .ipynb, .qmod
Paper link included
Will run pre-commit before commit

Key Assumptions

α_n renormalization: Uses authors' reference-code convention (required for Fig. 2)
Mode cutoff N_max=3: Matches Section IV.1
Coefficient rounding: 4 decimals (negligible perturbation)

References

G. M. Vinod and A. Shaji, arXiv:2401.04496
Classiq documentation: https://docs.classiq.io/

review-notebook-app · 2026-07-31T17:49:39Z

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github-actions · 2026-07-31T17:49:53Z

🔥 New notebook just dropped!

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

Tatgithub02 · 2026-08-01T10:17:30Z

@NadavClassiq please review the PR

TomerGoldfriend · 2026-08-02T12:06:20Z

Thank you @Tatgithub02 for this contribution. We will review it :-).
There are some test failures:

Could you please rebase your branch on the most updated main? This shall resolve the second test (this is due to a bug in our workflow that we fixed recently)
There are some lint error, could you please run pre-commit and commit again?

pip install pre-commit
pre-commit install

Let us know if you have any questions.

- 12-qubit Hamiltonian: 2257 Pauli strings - Exact evolution reproduces paper Fig. 2 - Classiq Suzuki-Trotter simulation - Validation: conservation laws verified Closes Classiq#580

Tatgithub02 · 2026-08-02T12:23:46Z

Thank you @Tatgithub02 for this contribution. We will review it :-). There are some test failures:

Could you please rebase your branch on the most updated main? This shall resolve the second test (this is due to a bug in our workflow that we fixed recently)

There are some lint error, could you please run pre-commit and commit again?
pip install pre-commit
pre-commit install
Let us know if you have any questions.

Thanks @TomerGoldfriend ! I've rebased onto the latest main and run pre-commit with the lint fixes committed. Let me know if anything else comes up.

…sign choices - Explain why custom Pauli algebra is used instead of SparsePauliTerm for Hamiltonian construction (converted to SparsePauliOp for suzuki_trotter) - Move PAULI_MATRICES dict to module level for reuse - Add forward-reference: sparse matrix powers Section 7 exact evolution - Explain motivation for classical Trotter emulation (isolates algorithmic error from shot noise) and reduce Fig 3 to 3 representative curves - Use synthesize(main) directly instead of create_model + synthesize - Replace ExecutionSession with calculate_state_vector (new Classiq API) - Update all downstream code: population_from_state_vector, batch params - Remove shot-noise error bars (state-vector gives exact probabilities) Co-authored-by: Cursor <cursoragent@cursor.com>

Tatgithub02 · 2026-08-15T15:09:48Z

@TomerGoldfriend I have resolved your queries. For further reviews - please mark the specific parts of code and add comments there. instead of all at top.
Thank you!

TomerGoldfriend · 2026-08-16T16:20:07Z

@TomerGoldfriend I have resolved your queries. For further reviews - please mark the specific parts of code and add comments there. instead of all at top. Thank you!

Thank you @Tatgithub02, we will go over the revised version. As for the comments, we work with ReviewNB, which is currently the most reasonable way to review jupyter notebooks. For markdown cells, it is not possible to comment on a specific line.
For further text review, I will make sure to copy the specific text in the comment, so it will be easy to find.

Co-authored-by: Cursor <cursoragent@cursor.com>

TomerGoldfriend · 2026-08-17T06:46:54Z

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+{


Environment
This notebook was developed and tested with classiq 1.19.1. Execution uses the current calculate_state_vector API (older releases used sampling helpers such as batch_sample / ExecutionSession.sample). The first cell installs dependencies and, on a fresh machine, performs the one-time Classiq authentication.
Run order. Use Restart kernel → Run All before reviewing plots or opening a PR. Section 13 depends on the Classiq time sweep (cell defining populations_trotter) finishing before the comparison and deviation plots - out-of-order execution causes NameError: populations_trotter is not defined. The sweep evaluates 41 time points with calculate_state_vector on the Classiq simulator (state-vector probabilities; no shot sampling).

You can delete this markdown cell (with the title Environment).
Our repo is always aligned with the classiq version. When new features arrive, we will update your notebook. It is always tested with the most updated classiq version.

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TomerGoldfriend · 2026-08-17T06:46:54Z

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+{


%pip install -U "classiq==1.19.1" numpy scipy matplotlib # import classiq # classiq.authenticate() # one-time browser login on a new machine

You can remove this

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TomerGoldfriend · 2026-08-17T06:46:54Z

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+{


but the author's reference implementation (shared with us directly, and against which this notebook was cross-checked term by term) applies the convention

Do you mean that you have the original paper implementation? it will be nice to run resource comparison between the qiskit implementation and the one with classiq herel; for example, comparing the CX count. This is just a suggestion of course, let me know if you want to do it, then probably we will need to put the qiskit implementation in a separate file, not to overload the notebook.

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TomerGoldfriend · 2026-08-17T06:46:54Z

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+{


Line #4. _PAULI_MUL = {
It is still not clear why can't you use Classiq's built-in SparsePauliOp. First, you can work with openfermion classes (FermionOperator and QubitOperator) and functions (jordan_wigner) , and then transform QubitOperator to qmod by the function qubit_op_to_qmod .

But if you do the Jordan Wigner by yourself, then even openfermion is not necessary, since you can do algebra with SparsePauliOp, like Pauli.X(0)*Pauli.Y(0). Please clarify what is missing.

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TomerGoldfriend · 2026-08-17T06:46:54Z

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+{


Line #2. TROTTER_ORDER = 1 # paper's choice: first-order (second order costs 2x depth)
BTW, classiq compiler gives something which is better than twice the depth.

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TomerGoldfriend · 2026-08-17T06:46:54Z

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+{


Line #1. write_qmod(main, "qft_simulation", decimal_precision=4)
You can remove the write_qmod, it is not required anymore.

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TomerGoldfriend · 2026-08-17T06:46:54Z

@@ -0,0 +1,2149 @@
+{


Line #2. pass
Why do you need this?

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TomerGoldfriend · 2026-08-17T06:48:42Z

@Tatgithub02 please move the notebook to the directory community/paper_implementation_project

TomerGoldfriend · 2026-08-17T06:49:07Z

@@ -1 +1 @@
-update_notebooks.sh


what is this change? please do not modify the .internal dir

Co-authored-by: Cursor <cursoragent@cursor.com>

… .internal Relocate the QFT notebook to paper_implementation_project, remove the write_qmod export and placeholder pass cell, qualify Trotter depth wording for Classiq synthesis, and restore .internal/update_outputs/main.sh. Co-authored-by: Cursor <cursoragent@cursor.com>

TomerGoldfriend · 2026-08-31T18:45:33Z

@Tatgithub02 what is the status here? did you complete the revised version according to our review?

Tatgithub02 · 2026-08-31T18:47:29Z

@TomerGoldfriend I recently got a new job, so was moving and packing, would start working on this tomorrow again!

github-actions Bot added the new notebook label Jul 31, 2026

Tatgithub02 added 4 commits August 2, 2026 17:47

Implement QFT Section IV.1 simulation

a01d1ce

- 12-qubit Hamiltonian: 2257 Pauli strings - Exact evolution reproduces paper Fig. 2 - Classiq Suzuki-Trotter simulation - Validation: conservation laws verified Closes Classiq#580

Auto-generate test file for QFT simulation

d4c00c9

Rename notebook to lowercase to match test file name

5450c23

Run pre-commit lint fixes

487fa17

Tatgithub02 force-pushed the implement/qft-section-iv-1 branch from 76f7e60 to 487fa17 Compare August 2, 2026 12:21

roie-d-classiq reviewed Aug 10, 2026

View reviewed changes

roie-d-classiq reviewed Aug 11, 2026

View reviewed changes

Comment thread community/paper_implementation_project/simulating_quantum_field_theories/qft_simulation.ipynb

Tatgithub02 and others added 2 commits August 13, 2026 12:31

Align notebook wording with calculate_state_vector execution

b4f4fe9

Rename metadata file to match lowercase notebook name

0a12ef1

Co-authored-by: Cursor <cursoragent@cursor.com>

TomerGoldfriend reviewed Aug 17, 2026

View reviewed changes

Tatgithub02 and others added 3 commits August 20, 2026 11:21

Build the Hamiltonian with Classiq SparsePauliOp algebra

cca589f

Co-authored-by: Cursor <cursoragent@cursor.com>

Revert .internal/update_outputs/main.sh to match main

d22ae68

		@@ -1 +1 @@
		update_notebooks.sh

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Conversation

Tatgithub02 commented Jul 31, 2026

Issue

What This Does

Implementation Details

Results

Files Included

Testing

Checklist

Key Assumptions

References

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review-notebook-app Bot commented Jul 31, 2026

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github-actions Bot commented Jul 31, 2026

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Tatgithub02 commented Aug 1, 2026

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Tatgithub02 commented Aug 15, 2026

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