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Quantum computing's flagship chemistry results don't say which state they found

1 points by purestatelabs 18d ago

cole_ilands 18d ago
[flagged]
purestatelabs 18d ago
I've submitted the underlying paper here twice before as a Zenodo link, but it didn't get much discussion. I wrote this new post to be more accessible to non-chemists, plus a couple of things have happened since the last time. First, IBM merged two PRs (364 and 366) to qiskit-addon-sqd on Sept 9 after I reported the issue. The docs for the symmetrize_spin option now clarify that it "does not guarantee that the state is an eigenvector of the total spin operator S^2". That covers one of the options. IBM hasn't commented on the paper itself, which I've recently updated to v2 on ChemRxiv. The short version of the post: IBM's released random-input control actually matches their quantum hardware on the smaller iron-sulfur cluster. Also, IBM's flagship paper, the published critique of it, and the RIKEN-IBM Fugaku follow-up all report energies without stating which spin state those energies belong to. If you rebuild the data for the largest [2Fe-2S] size they published, the lowest state has S^2 = 1.3711. They were aiming for a singlet, which should be 0. You can verify this without relying on my code: Hardware vs random (takes about 10 seconds in a browser, reading IBM's files directly): https://colab.research.google.com/github/PureStateLabs/sqd-spin-referee/blob/main/verify_hardware_vs_random.ipynb https://colab.research.google.com/github/PureStateLabs/sqd-s... Spin check (takes about 35 seconds, running PySCF on IBM's public integrals): https://github.com/PureStateLabs/sqd-spin-referee/blob/main/spin_inversion_is_not_singlet.py https://github.com/PureStateLabs/sqd-spin-referee/blob/main/... The last section of the post outlines exactly what would change my mind. If you try to reproduce a number and it doesn't match, let me know here. Paper: https://doi.org/10.26434/chemrxiv.15006382/v2 https://doi.org/10.26434/chemrxiv.15006382/v2 Data and code: https://doi.org/10.5281/zenodo.21359922 https://doi.org/10.5281/zenodo.21359922
purestatelabs 18d ago
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- gus_massa 16d ago
  Hi again! I like https://github.com/PureStateLabs/sqd-spin-referee/blob/main/SUMMARY.md https://github.com/PureStateLabs/sqd-spin-referee/blob/main/... better, the link at the top looks like standard AI generated stuff. Links to the previous posts: * https://news.ycombinator.com/item?id=49097083 https://news.ycombinator.com/item?id=49097083 (with my old comment) * https://news.ycombinator.com/item?id=49203707 https://news.ycombinator.com/item?id=49203707 (with an interesting comment by alpineidyll3) > [2Fe-2S] is two high-spin Fe(III) centres, each d5 with S = 5/2. I assumed S = 1/2 but a quick google search says that it may be 1/2 or 5/2. So it makes a lot of sense. > I've submitted the underlying paper here twice before as a Zenodo link, but it didn't get much discussion. There has been too much slop recently, I'm using a modified version of https://math.ucr.edu/home/baez/crackpot.html https://math.ucr.edu/home/baez/crackpot.html where you start at +5 instead of -5. Nature and Science adds -1. Zenodo adds +1. As I said before, this post makes sense. I'm still not sure it's correct and I didn't miss any detail, but it's not stupid-AI-slop.
  - purestatelabs 14d ago
    Thanks for digging up the old threads. The 1/2 you found is the reduced cluster: one extra electron turns one iron into Fe(II) with S = 2, and 5/2 coupled antiparallel to 2 leaves 1/2. This model is the oxidized form, two Fe(III), so the two 5/2 spins pair to 0. That's why the target is a singlet. Something I should have said in the first comment: the 35-second script prints S^2 = 3.50, not 1.3711, because it runs on a small test space. The 1.3711 is from the full-size calculation, and re-checking that takes about 11 hours on a 64-core machine. Both are far from 0, but if you ran the quick one expecting 1.3711 it would look like it didn't reproduce. Fair point on the blog post. I'm going to rewrite it now. The summary's the better link until then.

1 points by purestatelabs 18d ago

[flagged]

I've submitted the underlying paper here twice before as a Zenodo link, but it didn't get much discussion. I wrote this new post to be more accessible to non-chemists, plus a couple of things have happened since the last time. First, IBM merged two PRs (364 and 366) to qiskit-addon-sqd on Sept 9 after I reported the issue. The docs for the symmetrize_spin option now clarify that it "does not guarantee that the state is an eigenvector of the total spin operator S^2". That covers one of the options. IBM hasn't commented on the paper itself, which I've recently updated to v2 on ChemRxiv. The short version of the post: IBM's released random-input control actually matches their quantum hardware on the smaller iron-sulfur cluster. Also, IBM's flagship paper, the published critique of it, and the RIKEN-IBM Fugaku follow-up all report energies without stating which spin state those energies belong to. If you rebuild the data for the largest [2Fe-2S] size they published, the lowest state has S^2 = 1.3711. They were aiming for a singlet, which should be 0. You can verify this without relying on my code: Hardware vs random (takes about 10 seconds in a browser, reading IBM's files directly): https://colab.research.google.com/github/PureStateLabs/sqd-spin-referee/blob/main/verify_hardware_vs_random.ipynb https://colab.research.google.com/github/PureStateLabs/sqd-s... Spin check (takes about 35 seconds, running PySCF on IBM's public integrals): https://github.com/PureStateLabs/sqd-spin-referee/blob/main/spin_inversion_is_not_singlet.py https://github.com/PureStateLabs/sqd-spin-referee/blob/main/... The last section of the post outlines exactly what would change my mind. If you try to reproduce a number and it doesn't match, let me know here. Paper: https://doi.org/10.26434/chemrxiv.15006382/v2 https://doi.org/10.26434/chemrxiv.15006382/v2 Data and code: https://doi.org/10.5281/zenodo.21359922 https://doi.org/10.5281/zenodo.21359922

purestatelabs 18d ago

[dead]

gus_massa 16d ago
Hi again! I like https://github.com/PureStateLabs/sqd-spin-referee/blob/main/SUMMARY.md https://github.com/PureStateLabs/sqd-spin-referee/blob/main/... better, the link at the top looks like standard AI generated stuff. Links to the previous posts: * https://news.ycombinator.com/item?id=49097083 https://news.ycombinator.com/item?id=49097083 (with my old comment) * https://news.ycombinator.com/item?id=49203707 https://news.ycombinator.com/item?id=49203707 (with an interesting comment by alpineidyll3) > [2Fe-2S] is two high-spin Fe(III) centres, each d5 with S = 5/2. I assumed S = 1/2 but a quick google search says that it may be 1/2 or 5/2. So it makes a lot of sense. > I've submitted the underlying paper here twice before as a Zenodo link, but it didn't get much discussion. There has been too much slop recently, I'm using a modified version of https://math.ucr.edu/home/baez/crackpot.html https://math.ucr.edu/home/baez/crackpot.html where you start at +5 instead of -5. Nature and Science adds -1. Zenodo adds +1. As I said before, this post makes sense. I'm still not sure it's correct and I didn't miss any detail, but it's not stupid-AI-slop.
- purestatelabs 14d ago
  Thanks for digging up the old threads. The 1/2 you found is the reduced cluster: one extra electron turns one iron into Fe(II) with S = 2, and 5/2 coupled antiparallel to 2 leaves 1/2. This model is the oxidized form, two Fe(III), so the two 5/2 spins pair to 0. That's why the target is a singlet. Something I should have said in the first comment: the 35-second script prints S^2 = 3.50, not 1.3711, because it runs on a small test space. The 1.3711 is from the full-size calculation, and re-checking that takes about 11 hours on a 64-core machine. Both are far from 0, but if you ran the quick one expecting 1.3711 it would look like it didn't reproduce. Fair point on the blog post. I'm going to rewrite it now. The summary's the better link until then.