https://gilkalai.wordpress.com/2024/12/09/the-case-against-googles-claims-of-quantum-supremacy-a-very-short-introduction/ Combinatorics and more Gil Kalai's blog [cropped-gil-jirka] Skip to content * Home * 'Gina Says' * About + Pages o Conversation with the AI program GPT3 * Classes + Analysis of Boolean Functions (2013, Berkeley) + Game Theory, summer 2023 * ERC * Greatest Hits + Greatest Hits 2008-2015 + Greatest Hits 2016-2018 + Greatest Hits 2019-2022 * yvpyh shl hmtmtyqh - Some mathematical news The Case Against Google's Claims of "Quantum Supremacy": A Very Short Introduction. Posted on December 9, 2024 by Gil Kalai The 2019 paper "Quantum supremacy using a programmable superconducting processor" asserted that Google's Sycamore quantum computer, with 53 qubits and a depth of 20, performed a specific computation in about 200 seconds. According to Google's estimate, a state-of-the-art classical supercomputer would require approximately 10,000 years to complete the same computation. The Google experiment had two major components: 1. The "Fidelity Claims": Assertions regarding the fidelity of the samples produced by the quantum computer. 2. The "Supremacy Claims": Assertions that translated fidelity into a measure of advantage over classical computation. There are valid reasons to question both of these claims in the context of Google's 2019 experiment. In my view, these claims may reflect serious methodological mistakes rather than an objective scientific reality. I do not recommend treating Google's past or future claims as a solid foundation for policy-making decisions. Below is a brief review of the case against Google's 2019 claims of quantum supremacy: A) The "Supremacy" Assertions: Flawed Estimation of Classical Running Time A.1) The claims regarding classical running times were off by 10 orders of magnitude. A.2) Moreover, the Google team was aware that better classical algorithms existed. They had developed more sophisticated classical algorithms for one class of circuits and subsequently changed the type of circuits used for the "supremacy demonstration" just weeks before the final experiment. A.3) The 2019 Google paper states, "Quantum processors have thus reached the regime of quantum supremacy. We expect that their computational power will continue to grow at a double-exponential rate." It is surprising to encounter such an extraordinary claim in a scientific paper. B) The "Fidelity" Assertions: Statistically Unreasonable Predictions Indicating Methodological Flaws The google paper relies on a very simple a priori prediction of the fidelity based on the error-rates of individual components. (Formula (77).) B.1) The agreement between the a priori prediction and the actual estimated fidelity is statistically implausible ("too good to be true"): It is unlikely that the fidelities of samples from hundreds of circuits would agree within 10-20% with a simple formula based on the multiplication of the fidelities of individual components. In my opinion, this suggests a methodologically flawed optimization process, such as the one described in item C. B.2) The Google team provided a statistical explanation for this agreement based on three premises. The first premise is that the fidelities for the individual components are exact up to +-20%. The second premise is that this +-20% instability is unbiased. The third premise is that all these fidelities for individual components are statistically independent. These premises are unreasonable and they contradict various other experimental findings. B.3) As of now, the error rates for individual components have not been released by the Google team. (Most recently, in May 2023, they promised "to push" for this data.) Analysis of the partial data provided for readout errors reinforces these concerns. C) The Calibration Process: Evidence of Undocumented Global Optimization According to the Google paper, calibration was performed prior to running the random circuit experiments and was based on the behavior of 1- and 2-qubit circuits. This process involved modifying the definitions of 1-gates and 2-gates to align with how the quantum computer operates. C.1) Statistical evidence suggests that the calibration process involved a methodologically flawed global optimization process. (This concern applies even to Google's assertions about the fidelity of the smallest 12-qubit circuits.) C.2) Non-statistical evidence also supports this claim. For example, contrary to the description provided by the Google team, it was revealed that they supplied an outdated calibration version (for the experimental circuits) to the Julich Research Center scientists involved in the experiment. This calibration was later further modified after the experiment was conducted. (This discrepancy is also reflected in a video released by Google particularly between 2:13-3:07.) C.3) The Google team has not disclosed their calibration programs, citing them as a commercial secret. For technical reasons, they were also unable to share the inputs for the calibration program, although they promised to do so in future experiments--a promise that has not yet been fulfilled. google-slide13 A slide from my 2019 lecture "The Google quantum supremacy demo" ( post), highlights that the error rates for two-qubit gates e_g have not yet been provided by the Google team as of today (Dec. 2024). D) Comparing Google with IBM As far as we know, there is a significant gap (in favor of Google) between what IBM quantum computers--which are in some ways more advanced than Google's quantum computers--can achieve for random circuit sampling and what Google claims, even for circuits with 7-12 qubits. While one might argue that Google's devices or team are simply better, in my view, this gap more likely reflects methodological issues in Google's experiments. E) (Not) Adopting Suggestions for Better Control In our discussions with the Google team, they endorsed several of our suggestions for future experiments aimed at improving control over the quality of their experiments. However, in practice, later experiments did not implement any of these suggestions. Moreover, the structure of these later experiments makes them even harder to verify compared to the 2019 experiment. Additionally, unlike the 2019 experiment, the data for a subsequent random circuit sampling experiment does not include the amplitudes computed for the experimental circuits, further complicating efforts to scrutinize the results. F) My Personal Conclusion Google Quantum AI's claims (including published ones) should be approached with caution, particularly those of an extraordinary nature. These claims may stem from significant methodological errors and, as such, may reflect the researchers' expectations more than objective scientific reality. I do not recommend treating Google's past or future claims as a solid basis for policy-making decisions. G) Remarks G.1) Google's supremacy claims (from the 2019 paper) have been refuted in a series of papers by several groups. This began with work by IBM researchers Pednault et al. shortly after Google's original paper was published and continued with studies by Pan and Zhang; Pan, Chen, and Zhang; Kalachev, Panteleev, and Yung; Gao et al.; Liu et al.; and several other groups. For further details, see this post and the associated comment section, as well as this post. G.2) Google now acknowledges that using the tensor network contraction method, their 2019 53-qubit result can be computed classically in less than 200 seconds. However, in their more recent 2023/24 paper, "Phase Transitions..." (see Table 1), they claim that with 67 to 70 qubits, classical supercomputers would require many years to generate 1 million such bitstrings, even with tensor network contraction. G.3) Items B) and C) highlights methodological issues with Google's fidelity assertions, even for 12-qubit circuits. These concerns persist independently of the broader question of quantum supremacy for larger circuits, where the fidelity assertions are taken at face value. G.4) For a more comprehensive view of our study of Google's fidelity claims, refer to the following papers: * Y. Rinott, T. Shoham, and G. Kalai, Statistical Aspects of the Quantum Supremacy Demonstration, (2020) Statistical Science (2022) * G. Kalai, Y. Rinott and T. Shoham, Google's 2019 "Quantum Supremacy" Claims: Data, Documentation, & Discussion (2022) (see this post). * G. Kalai, Y. Rinott and T. Shoham, Questions and Concerns About Google's Quantum Supremacy Claim (2023) (see this post). * G. Kalai, Y. Rinott and T. Shoham, Random circuit sampling: Fourier expansion and statistics. (2024) (see this post) These papers describe an ongoing project with Yosi Rinott and Tomer Shoham, supported by Ohad Lev and Carsten Voelkmann. Together with Carsten, we plan to expand our study and apply our tools to other experiments. Additionally, see my earlier paper: * G. Kalai, The argument against quantum computers, the quantum laws of nature, and Google's supremacy claims, (2020) The Intercontinental Academia Laws: Rigidity and Dynamics (M. J. Hannon and E. Z. Rabinovici, eds.), World Scientific, 2024. arXiv:2008.05188. G.5) There is also supporting evidence for Google's 2019 claims, such as a 2020 replication by a group from the University of Science and Technology of China (USTC) and later verifications of some of Google's fidelity estimations. G.6) There are some additional concerns regarding the Google experiment. In particular, there are problematic discrepancies between the experimental data, the Google noise model, and simulations. G.7) In my opinion, the main current challenge for experimental quantum computing is to improve the quality of two-qubit gates and other components, as well as to carefully study the quality of quantum circuits in the 5-20 qubit regime. Experiments on quantum error correction for larger circuits are also important. H) Hype and Bitcoin I usually don't mind "hype" as a reflection of scientists' enthusiasm for their work and the public's excitement about scientific endeavors. However, in the case of Google, some caution is warranted, as the premature claims in 2019 may have had significant consequences. For example, following the 2019 "supremacy" announcement, the value of Bitcoin dropped (around October 24, 2019, after a period of stability) from roughly $9,500 to roughly $8,500 in just a few days, representing a loss for investors of more than ten billion dollars. (The value today is around $100,000.) Additionally, Google's assertions may have imposed unrealistic challenges on other quantum computing efforts and encouraged a culture of undesirable scientific methodologies. BNP5 Sergio Boixo, Hartmut Neven, and John Preskill in a video "Quantum next leap: Ten septillions years beyond-classic" I) Update (Dec. 10): The Wind in the Willow Yesterday, Google Quantum AI announced that their "Willow" quantum computer "performed a standard benchmark computation in under five minutes that would take one of today's fastest supercomputers 10 septillion (that is, 10^25) years." As far as I know there is no paper with the details. Google AI team announced also the appearance in Nature of their recent paper on distance-5 and distance-7 surface codes. It is asserted that the distance-7 codes exhibit an improvement of a factor of 2.4 compared to the physical qubits. The ratio of improvement L from distance-5 to distance-7 is 2.14. (We mentioned it in an August post following a comment by phan ting.) We did not study yet these particular claims by Google Quantum AI, but my general conclusion apply to them "Google Quantum AI's claims (including published ones) should be approached with caution, particularly those of an extraordinary nature. These claims may stem from significant methodological errors and, as such, may reflect the researchers' expectations more than objective scientific reality." (Our specific contention points are relevant to Google's newer supremacy experiments but not directly to the quantum error-correction experiment.) There is a nice very positive blog post over SO about the new developments where Scott wrote: "besides the new and more inarguable Google result, IBM, Quantinuum, QuEra, and USTC have now all also reported Random Circuit Sampling experiments with good results." For me, the gap between Google and IBM for RCS is a serious additional reason not to take the Google assertions seriously (item D) and and if I am wrong I will gladly stand corrected. Share this: * Facebook * Reddit * Twitter * Like Loading... Related This entry was posted in Computer Science and Optimization, Physics, Quantum and tagged Quantum computation, quantum supremacy. Bookmark the permalink. - Some mathematical news 16 Responses to The Case Against Google's Claims of "Quantum Supremacy": A Very Short Introduction. 1. [5b2e] gasarchf90cbc904d says: December 9, 2024 at 6:57 pm what is the connection between Google's hyped claims and Bitcoin falling? How does one cause the other? Reply + [0d9c] Gil Kalai says: December 9, 2024 at 8:46 pm When the 2019 supremacy claims were released (or rather leaked) there were a lot of claims that this means that quantum computers are near and hence that the cryptography needed for bitcoins will be breakable and that bitcoin will loose its value. (Of course, if a major step toward quantum computers is made that suggests that they are expected in the very near future then this could be a reasonable reaction.) It is reasonable to think that the 2019 supremacy excitement caused bitcoin falling around Oct 24, 2019 (and I suppose this was mentioned in the media) but it would be difficult to verify it. It is hard to tell if a much publicized claim tomorrow of "quantum advantage" that asserts that a quantum circuit can do in 100 seconds what would take a classical computer Googol years will have a similar effect. (Googol is 1 with 100 zeroes.) It is worth mentioning that the 2019 advantage argument was based on a careful interpolation argument while the later paper from 2024/2024 (G.2) was based on a much less elaborate argument of basically extrapolating from three disjoint circuits running in parallel to a circuit with connections between these components. As far as I remember, the 2023 paper was not hyped, did not make outrageous claims, and was centered around phase transition phenomena. Reply 2. Pingback: Fan Dui Gu Ge Sheng Cheng "Liang Zi Ba Quan "De Lun Dian - Pian Zhi De Ma Nong 3. [20e2] Tuomas Laakkonen says: December 10, 2024 at 8:24 am Hi, nice post. Do you have a specific reference in mind for your points B1 and B2? I'm interested because I have done some experiments recently running some small Hadamard-test-based quantum algorithms (of course, not trying to claim any advantage) and have seen excellent agreement with these kinds of simplistic error models. Perhaps the difference is in measuring expectation values vs approximating the whole output distribution? Reply + [0d9c] Gil Kalai says: December 10, 2024 at 9:57 am Hi Tuomas, Points B1 abd B2 are discussed in Section 3 of our paper Questions and Concerns About Google's Quantum Supremacy Claim. On which platform did you experiment your quantum algorithms? Reply 4. Pingback: Start Up No.2351: our upturned media landscape, TikTok fails to halt US axe, Bluesky gets spam, seize that plane!, and more | The Overspill: when there's more that I want to say 5. [0d9c] Gil Kalai says: December 10, 2024 at 10:46 am Yesterday, Google Quantum AI announced that their "Willow" quantum computer" performed a standard benchmark computation in under five minutes that would take one of today's fastest supercomputers 10 septillion (that is, 10^25) years", see https:/ /blog.google/technology/research/google-willow-quantum-chip/. As far as I know there is no paper with the details. An earlier peace of news with "septillions" was that Russian state-run broadcasters sue YouTube for $21 septillion. (See also The Impact of Russia's $20 Decillion Fine on Google's Operations and Free Speech.) Reply + [2a81] Gali Weinstein says: December 10, 2024 at 6:10 pm "As far as I know there is no paper with the details". Google refers to a Nature paper from December 9, 2024: https:// www.nature.com/articles/s41586-024-08449-y(preprint of the paper: https://arxiv.org/abs/2408.13687) The above paper demonstrates the implementation of distance-5 and distance-7 surface codes, showing exponential suppression of logical error rates as code distance increases. This confirms below-threshold operation. This system processes error syndromes at a cycle duration of 1.1 us. The above paper reports logical error suppression by a factor of approximately 2.14 for distance-7 codes and logical lifetimes exceeding physical qubit lifetimes by 2.4x, etc. The Nature paper presents the technical achievements attributed to Willow, particularly the quantum error correction and scalability. Thus, from the quantum supremacy point of view, Sycamore's role in the race between classical and quantum computers has largely been eclipsed by Willow, making Sycamore less relevant for demonstrating quantum supremacy. Effectively it is out of the race... Willow re-establishes and dramatically expands the quantum advantage, making Sycamore's supremacy demonstration less relevant in the current competitive landscape. Willow's advancements in error correction and real-world application push the focus away from Sycamore's one-off supremacy task. However, Sycamore remains historically significant. Willy The WillowTree. Reply o [0d9c] Gil Kalai says: December 10, 2024 at 10:32 pm Thanks Gali, I think that there is no paper supporting the "septillion" advantage claim and it was a questionable call to make such a dramatic announcement and hype it without a paper. If my concerns regarding Google's methodology is correct than adding qubits and changing the name is not a cure. These concerns apply to Google's experiments with 12 qubits! I am aware of the quantum error correction paper. (Of course it should also be scrutinized.) o [6356] Frank says: December 11, 2024 at 6:13 am To my understanding Sycamore's demonstration result has been super-seeded by two peer-reviewed real-life experiments with classic computers from labs in China. One may argue Google could/would/should tweak Sycamore to make its supremacy claim last a bit longer, but the truth is Sycamore is only a supremacy claim attempt which had later been outpaced by classic computers. o [e758] Matthew Cory says: December 11, 2024 at 9:19 pm None of the people on these blogs or companies seem to have a deep background in quantum field theory. Sorry, but we are dealing with infinite-dimensional fields, and there is no evidence for any ability to do analog error correction on them. Nowhere in field theory do we assume a constant error rate assumed by the threshold theorem. Everything we know theoretically and experimentally points against the idea. Digital quantum computing was mostly founded by computer scientists without a strong theoretical background in physics. Huge amounts of misunderstanding swirl about even the most basic problems, such as renormalization. The Wightman axioms have overly strong linearity assumptions, and this has confused people for decades about the measurement problem. Few seem to understand that you can use nonlinear functionals of source functions to construct quantum field operators. As Bill Unruh rightly said, Feynman's path integrals set physics back for decades. Superposition, nonlocality, etc. are trivial when dealing with an ontology of fields. Even GR follows easily from Deser's use of the Palatini formalism. With QCs, we are dealing with analog chaos. Google is getting desperate and ginning up systems with extremely small numbers of qubits to prove nothing but an ability to do some careful calibration. Gil is right. 6. [7433] Yuri Gurevich says: December 10, 2024 at 5:57 pm A great post. Thank you for your effort to make the story comprehensible. I am waiting though for a comprehensible exposition of your principle arguments about natural limitations of quantum computing. Reply + [0d9c] Gil Kalai says: December 10, 2024 at 10:27 pm Dear Yuri, many thanks "I am waiting though for a comprehensible exposition of your principle arguments about natural limitations of quantum computing." (As you know) I am trying to make my argument clear and to write and rewrite it to make it comprehensible. On this matter I think that my argument is not ironclad, that the debate is serious, and that experimental efforts (which are methodologically sound) are crucial. Here is one of my attempts to introduce my argument. The Argument Against Quantum Computers - A Very Short Introduction Reply 7. Pingback: Shtetl-Optimized >> Blog Archive >> The Google Willow thing 8. Pingback: Shtetl-Optimized >> Weblog Archive >> The Google Willow factor - Aiquantumtools.com 9. 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