https://scottaaronson.blog/?p=8525 Shtetl-Optimized The Blog of Scott Aaronson If you take nothing else from this blog: quantum computers won't solve hard problems instantly by just trying all solutions in parallel. --------------------------------------------------------------------- << Podcasts! The Google Willow thing Yesterday I arrived in Santa Clara for the Q2B (Quantum 2 Business) conference, which starts this morning, and where I'll be speaking Thursday on "Quantum Algorithms in 2024: How Should We Feel?" and also closing the conference via an Ask-Us-Anything session with John Preskill. (If you're at Q2B, reader, come and say hi!) And to coincide with Q2B, yesterday Google's Quantum group officially announced "Willow," its new 105-qubit superconducting chip with which it's demonstrated an error-corrected surface code qubit as well as a new, bigger quantum supremacy experiment based on Random Circuit Sampling. I was lucky to be able to attend Google's announcement ceremony yesterday afternoon at the Computer History Museum in Mountain View, where friend-of-the-blog-for-decades Dave Bacon and other Google quantum people explained exactly what was done and took questions (the technical level was surprisingly high for this sort of event). I was also lucky to get a personal briefing last week from Google's Sergio Boixo on what happened. Meanwhile, yesterday Sundar Pichai tweeted about Willow, and Elon Musk replied "Wow." It cannot be denied that those are both things that happened. Anyway, all yesterday, I then read comments on Twitter, Hacker News, etc. complaining that, since there wasn't yet a post on Shtetl-Optimized, how could anyone possibly know what to think of this?? For 20 years I've been trying to teach the world how to fish in Hilbert space, but (sigh) I suppose I'll just hand out some more fish. So, here are my comments: 1. Yes, this is great. Yes, it's a real milestone for the field. To be clear: for anyone who's been following experimental quantum computing these past five years (say, since Google's original quantum supremacy milestone in 2019), there's no particular shock here. Since 2019, Google has roughly doubled the number of qubits on its chip and, more importantly, increased the qubits' coherence time by a factor of 5. Meanwhile, their 2-qubit gate fidelity is now roughly 99.7% (for controlled-Z gates) or 99.85% (for "iswap" gates), compared to ~99.5% in 2019. They then did the more impressive demonstrations that predictably become possible with more and better qubits. And yet, even if the progress is broadly in line with what most of us expected, it's still of course immensely gratifying to see everything actually work! Huge congratulations to everyone on the Google team for a well-deserved success. 2. I already blogged about this!!! Specifically, I blogged about Google's fault-tolerance milestone when its preprint appeared on the arXiv back in August. To clarify, what we're all talking about now is the same basic technical advance that Google already reported in August, except now with the PR blitz from Sundar Pichai on down, a Nature paper, an official name for the chip ("Willow"), and a bunch of additional details about it. 3. Scientifically, the headline result is that, as they increase the size of their surface code, from 3x3 to 5x5 to 7x7, Google finds that their encoded logical qubit stays alive for longer rather than shorter. So, this is a very important threshold that's now been crossed. As Dave Bacon put it to me, "eddies are now forming"--or, to switch metaphors, after 30 years we're now finally tickling the tail of the dragon of quantum fault-tolerance, the dragon that (once fully awoken) will let logical qubits be preserved and acted on for basically arbitrary amounts of time, allowing scalable quantum computation. 4. Having said that, Sergio Boixo tells me that Google will only consider itself to have created a "true" fault-tolerant qubit, once it can do fault-tolerant two-qubit gates with an error of ~10^-6 (and thus, on the order of a million fault-tolerant operations before suffering a single error). We're still some ways from that milestone: after all, in this experiment Google created only a single encoded qubit, and didn't even try to do encoded operations on it, let alone on multiple encoded qubits. But all in good time. Please don't ask me to predict how long, though empirically, the time from one major experimental QC milestone to the next now seems to be measured in years, which are longer than weeks but shorter than decades. 5. Google has also announced a new quantum supremacy experiment on its 105-qubit chip, based on Random Circuit Sampling with 40 layers of gates. Notably, they say that, if you use the best currently-known simulation algorithms (based on Johnnie Gray's optimized tensor network contraction), as well as an exascale supercomputer, their new experiment would take ~300 million years to simulate classically if memory is not an issue, or ~10^25 years if memory is an issue (note that a mere ~10^10 years have elapsed since the Big Bang). Probably some people have come here expecting me to debunk those numbers, but as far as I know they're entirely correct, with the caveats stated. Naturally it's possible that better classical simulation methods will be discovered, but meanwhile the experiments themselves will also rapidly improve. 6. Having said that, the biggest caveat to the "10^25 years" result is one to which I fear Google drew insufficient attention. Namely, for the exact same reason why (as far as anyone knows) this quantum computation would take ~10^25 years for a classical computer to simulate, it would also take ~10^25 years for a classical computer to directly verify the quantum computer's results!! (For example, by computing the "Linear Cross-Entropy" score of the outputs.) For this reason, all validation of Google's new supremacy experiment is indirect, based on extrapolations from smaller circuits, ones for which a classical computer can feasibly check the results. To be clear, I personally see no reason to doubt those extrapolations. But for anyone who wonders why I've been obsessing for years about the need to design efficiently verifiable near-term quantum supremacy experiments: well, this is why! We're now deeply into the unverifiable regime that I warned about. 7. In his remarks yesterday, Google Quantum AI leader Hartmut Neven talked about David Deutsch's argument, way back in the 1990s, that quantum computers should force us to accept the reality of the Everettian multiverse, since "where else could the computation have happened, if it wasn't being farmed out to parallel universes?" And naturally there was lots of debate about that on Hacker News and so forth. Let me confine myself here to saying that, in my view, the new experiment doesn't add anything new to this old debate. It's yet another confirmation of the predictions of quantum mechanics. What those predictions mean for our understanding of reality can continue to be argued as it's been since the 1920s. 8. Cade Metz did a piece about Google's announcement for the New York Times. Alas, when Cade reached out to me for comment, I decided that it would be too awkward, after what Cade did to my friend Scott Alexander almost four years ago. I talked to several other journalists, such as Adrian Cho for Science. 9. No doubt people will ask me what this means for superconducting qubits versus trapped-ion or neutral-atom or photonic qubits, or for Google versus its many competitors in experimental QC. And, I mean, it's not bad for Google or for superconducting QC! These past couple years I'd sometimes commented that, since Google's 2019 announcement of quantum supremacy via superconducting qubits, the trapped-ion and neutral-atom approaches had seemed to be pulling ahead, with spectacular results from Quantinuum (trapped-ion) and QuEra (neutral atoms) among others. One could think of Willow as Google's reply, putting the ball in competitors' courts likewise to demonstrate better logical qubit lifetime with increasing code size (or, better yet, full operations on logical qubits exceeding that threshold, without resorting to postselection). The great advantage of trapped-ion qubits continues to be that you can move the qubits around (and also, the two-qubit gate fidelities seem somewhat ahead of superconducting). But to compensate, superconducting qubits have the advantage that the gates are a thousand times faster, which makes feasible to do experiments that require collecting millions of samples. 10. Of course the big question, the one on everyone's lips, was always how quantum computing skeptic Gil Kalai was going to respond. But we need not wonder! On his blog, Gil writes: "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.' " Most of Gil's post is devoted to re-analyzing data from Google's 2019 quantum supremacy experiment, which Gil continues to believe can't possibly have done what was claimed. Gil's problem is that the 2019 experiment was long ago superseded anyway: 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. I predict that Gil, and others who take it as axiomatic that scalable quantum computing is impossible, will continue to have their work cut out for them in this new world. Update: Here's Sabine Hossenfelder's take. I don't think she and I disagree about any of the actual facts; she just decided to frame things much more negatively. Ironically, I guess 20 years of covering hyped, dishonestly-presented non-milestones in quantum computing has inclined me to be pretty positive when a group puts in this much work, demonstrates a real milestone, and talks about it without obvious falsehoods. Email, RSS Follow This entry was posted on Tuesday, December 10th, 2024 at 10:10 am and is filed under Quantum. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site. 25 Responses to "The Google Willow thing" 1. David Murphy Says: Comment #1 December 10th, 2024 at 10:53 am For a non Quantum guy, thanks for the explanation and references. We are living through great change but humanity through our acts of violence confounds me. Keep up the excellent work. 2. Checking our forecast for quantum computing in 2024 - foreXiv Says: Comment #2 December 10th, 2024 at 10:55 am [...] what it's worth, Google has decided to equate "fault-tolerance" with a logical error rate below 1e-6. It's all a bit [...] 3. Cyrus Says: Comment #3 December 10th, 2024 at 11:12 am Hi Scott, Sorry that this is off-topic, but I couldn't resist asking your opinion about dramatic recent global events. The Assad regime in Syria collapsed suddenly, in only a span of fourteen days or so, after a civil war that lasted fourteen *years.* I don't think anyone expected this, even the rebels themselves--especially because the conflict was frozen since 2020! So I have two questions for you about this--one straightforward, and one hypothetical. 1. How do you feel about Assad? Do you think the collapse of his regime is a good thing for Syria? Do you think he was truly a brutal ruthless dictator, or was he somewhat misunderstood, the atrocities exaggerated? Do you think the rebels are better for Syria? 2. I recently learned that Bashar's son, Hafez, recently got his PhD in algebraic number theory in Moscow. By all accounts he's a smart mathematician. This evokes an interesting hypothetical: if Hafez al-Assad was pursuing a PhD at UT Austin in theoretical computer science or quantum information, would you work with him? Would you treat him differently than other students? What does your moral compass say about working with a student whose father is a ruthless dictator? 4. Scott Says: Comment #4 December 10th, 2024 at 11:43 am Cyrus #3: Here's what I wrote on Facebook: Good riddance to Syria's murderous dictator, and best wishes to its new, possibly slightly more reform-minded murderous dictators Assad was a monster. I'm cautiously hopeful that the Syrian people finally have the chance to choose a better path, but of course I'm acutely aware of the long history of revolutions in the Middle East (and elsewhere) that replaced despotisms by even worse ones. In any case, I'm of course gratified that Iran's terror axis has been weakened by the regime change in Syria. If Hafez al-Assad disavowed the murderous ideology of his father (as, for example, the "Son of Hamas" famously did), then there'd be no issue whatsoever about doing math with him; it would even be a privilege. Collaborating with someone who believes you deserve to die as a Zionist infidel would of course present some practical safety problems. I guess I'm lucky that that issue hasn't arisen even once in 27 years of research, including with at least four Iranians. 5. Some physicist Says: Comment #5 December 10th, 2024 at 11:48 am Do you know why did Google perform the random circuit sampling with only 67 qubits when the chip has 105 qubits? (I'm getting the 67 figure from https://www.nature.com/articles/ s41586-024-07998-6, which is what Google's blog post links to) Did they attempt RCS with 105 qubits and failed ? I still have in mind my threshold number of qubits at 76, because Avogadro's constant is 10^23 =2^76, and if you exceed this threshold then it means that it's impossible for the quantum state to be encoded classically in some magical way by the particles in the system, and that the quantum system really does use an exponential Hilbert space from nature instead of encoding all the possible states of the Hilbert space in some classical way. I'd also be more convinced if they did some test such as running some unitary and then its inverse and testing the error rate of that, because XEB can't be verified and can only be extrapolated. 6. Gil Kalai Says: Comment #6 December 10th, 2024 at 11:56 am Hi Scott, You 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." Scott, are you sure about IBM? One of my reasons (beside the "skeptillions" ) not to take the Google claims too seriously is that the largest IBM's random circuit sampling experiment I am aware of is for 7 qubits and I am not aware of IBM's RCS experiments with good results. (This is item "D" in my post and if I am wrong I will gladly stand corrected.) 7. Cyrus Says: Comment #7 December 10th, 2024 at 12:07 pm Thanks for your reply. I really disagree about one thing, though. I highly doubt that Hafez (or Bashar, for that matter) would view you as a Zionist infidel. Bashar is not an idealogue and not particularly religious. Before 2011, most Western leaders saw him as a pro-Western secular dictator. He briefly flirted with normalizing relations with Israel before 2011. Of course he's come to rely on Iranian military support--but not because he's particularly sympathetic to Iranian islamist ideology, but just because nobody else would support him. Wikileaks released a trove of Assad emails during the revolution. It's clear that he's not particularly religious (possible even an athetist), nor is he ideological. He very likely doesn't give a shit about Israel and Palestine one way or the other. What he cares about most is keeping his family wealthy and in power--and in particular, preserving his family's lavish lifestyle--the palaces, the fancy cars, and especially funding his wife's extravagant spending habits (jewelry and art and designer clothes etc). To be honest, a secular autocrat who mostly cares about his family's power and lifestyle would be much safer for Israel than a failed state ruled by Islamist jihadists. You're aware that al-Jolani used to be leader of al Qaeda in Iraq? That he still has a 10 million dollar state department bounty on his head for terrorism? 8. Christopher Greene Says: Comment #8 December 10th, 2024 at 12:19 pm IBM's heron chip has been out for about year, with ostensibly similar error rates and more qubits (but a different topology). What are the main advantages of Willow that allowed them to run error correction codes on this chip? Could heron have run error correction and achieved this? Can the error correction code implemented on Willow be ported to Heron? When a logical gate gets applied to a logical qubit does it essentially just get "mixed in" to be the error correction step? Are there topological requirements when you want to operate a two logical qubit gate? 9. Scott Says: Comment #9 December 10th, 2024 at 12:20 pm Some physicist #5: Sorry, I don't know the answer to that, nor do I know if they did the inversion test (but note that doubling the circuit depth would square their signal-to-noise ratio). I guess we'll wait for the paper on their new RCS experiment (or I can try asking them at Q2B). 10. Scott Says: Comment #10 December 10th, 2024 at 12:23 pm Gil Kalai #6: IBM never uses the term "quantum supremacy." Instead they talk about the "quantum volume" of their current device. But if you look at the definition of their "quantum volume" metric, it's directly based on Random Circuit Sampling. 11. Scott Says: Comment #11 December 10th, 2024 at 12:25 pm Christopher Greene #8: Excellent question! I hope someone from IBM and/or Google will chime in about why IBM didn't demonstrate the same benchmark. 12. The Case Against Google's Claims of "Quantum Supremacy": A Very Short Introduction. | Combinatorics and more Says: Comment #12 December 10th, 2024 at 12:38 pm [...] is a nice very positive blog post over SO about the new developments where Scott wrote: "besides the new and more inarguable Google result, [...] 13. Gil Kalai Says: Comment #13 December 10th, 2024 at 1:07 pm Scott, IBM do use the term "random circuit sampling" and have a paper where they run an RCS experiment with six qubits. In addition, indeed, "quantum volume" is a closely related notion and IBM's record for quantum volume is 2**9. Both these results are considerably weaker compared to Google's assertions from 2019 (not to speak about newer papers). As I said in my post, from what I know, there is a large gap between IBM's and Google's RCS abilities (and if you have some more information I will correct myself if needed), and, in the context of other concerns about Google's methodology and Google's very fantastic claims, this gives, in my opinion, a reason to doubt the Google's assertions. Also, are you sure that QuEra have reported Random Circuit Sampling experiments with good results? Can you give a link or a reference? 14. Alexis Morvan Says: Comment #14 December 10th, 2024 at 1:30 pm Some physicist#5: the manuscript you quote was run on a sycamore device, not a willow device. Hence why we only used a smaller number of qubits in this experiment. The announcement made yesterday was about a new RCS experiment run on the willow device. For your question about inverting the unitary, we actually do it in figure 4b of the manuscript you quote. We called it Loschmidt experiment in the figure/texts. 15. Scott Says: Comment #15 December 10th, 2024 at 2:01 pm Gil Kalai #13: Yes, IBM talks about RCS, but never about "quantum supremacy." QuEra did a 48-qubit IQP circuit. That was then classically simulated, but if you just want to see that the circuit fidelity degrades like the gate fidelity to the power of the number of gates--which of course has always been your central point of contention--then that already suffices. For that statement, my point stands: you're no longer arguing against one experiment, but against a half-dozen separate experiments. 16. triceratops Says: Comment #16 December 10th, 2024 at 2:07 pm Pop media is buzzing about a revolutionary new quantum machine from Google that runs a gazillion times faster than a regular desktop by executing programs in parallel universes. The truth appears to be substantially more subtle. As far as I can tell (and I might be way off-base here), RCS is a demonstration that your quantum computer runs test case quantum circuits the way you'd expect a quantum computer to run them, to a level of detail that would be infeasible to fake with a classical computer. It's a specialized problem without any direct utility outside of the benchmark. To frame it as a car analogy: we've proved the engine is running, but that doesn't demonstrate that the vehicle will get us anywhere. Something about the narrow, contrived nature of the RCS problem makes "supremacy" feel like a stretch, despite technically fitting the definition. Am I wrong to want a more bombastic result out of a QC experiment before I'm ready to declare the age of quantum computing is upon us? 17. Scott Says: Comment #17 December 10th, 2024 at 2:20 pm triceratops #16: I've pretty much given up on trying to calibrate a single message. Different people need different messages depending on what misconception they have. If someone thinks we're about to get personal QCs that will speed up everything we do, they need to be told that "the age of QC" is not upon us (and indeed, might never be). If, on the other hand, someone thinks QC is all a scam or a misconception, and quantum error-correction can never work in the real world, they need to be told that "the age of QC" is now upon us. 18. Cyrus Says: Comment #18 December 10th, 2024 at 2:29 pm One thing I like about Assad is that he defies popular expectations of who a dictator should be. What's a Middle Eastern dictator in the popular imagination? He's tall and strong, square-jawed and handsome. He's had experience as a soldier. He's a fighter. He's socially intelligent and charismatic. Assad is none of those things. Only a couple years before assuming power, he was a mild-mannered opthamologist in London. His brother was the strong, charismatic one--and his brother's death paved the way for him to become dictator. People who knew Bashar in his London days remembered him as a quiet, socially awkward, "geeky I.T. guy"--a nerd. He's gawky and chinless and awkward. He's soft-spoken. He's not charismatic or conventionally attractive. He spent his formative years studying. He can't fight, he doesn't even play sports. So yes, he's a "geek"--and a fearsome dictator. Surely it's good to show young male geeks an example of someone who achieved fearsome power despite all those impediments?Isn't it good for representation etc. that he showed the world that you don't have to be good looking or charismatic to be a powerful ruler? That you can even be a nerd and do all those things? 19. RubeRad Says: Comment #19 December 10th, 2024 at 2:43 pm noob question: how many qubits would it take to implement Shor's factorization for browser-standard 2048-bit keys? 20. Gabe Durazo Says: Comment #20 December 10th, 2024 at 3:31 pm Okay, so if this is officially Shtetl-Optimized-Approved, then I can be excited. As someone who's only watched from afar for awhile now, and who remembers your skepticism to D-Wave back in the day, I'm curious about D-Wave's role in all this, since they were acquired by Google. Does this mean they actually had something back then after all? Or did it end up being more of an "acquihire" and this is from a different tech tree, so to speak? 21. Scott Says: Comment #21 December 10th, 2024 at 4:07 pm Cyrus #18: I know you're trolling me, but I feel like you kind of turn in your geek card at the point when you're slaughtering 500,000 people because they challenged your absolute rule. 22. Scott Says: Comment #22 December 10th, 2024 at 4:10 pm RubeRad #19: noob question: how many qubits would it take to implement Shor's factorization for browser-standard 2048-bit keys? At least 4000 logical qubits. With known error-correcting codes, that means easily more than a million physical qubits (more or less depending on the gate fidelity). 23. Gil Kalai Says: Comment #23 December 10th, 2024 at 4:12 pm Scott, The two central points of contention presented in my post regarding the Google 2019 paper are the following: 1) The calibration process appears to exhibit an undocumented and methodologically flawed global optimization process. 2) The circuit fidelity degrades like the gate fidelity to the power of the number of gates *in a statistically unreasonable way*. The first point may well be relevant for Google's 2023/2024 advantage paper and to the new septillion paper. (These specific contention points do not seem to be directly relevant to the Google error correcting claims and not to the QuEra IQP experiment.) You missed the point about IBM. I don't mind if they use the term quantum supremacy or not. From what I know the quality of RCS samples produced by IBM is considerably lower than that produced by Google and in my opinion this likely follows from methodologically flawed methods that Google uses related to contentions 1) and 2). 24. Scott Says: Comment #24 December 10th, 2024 at 4:13 pm Gabe Durazo #20: D-Wave was not acquired by Google. I have no idea where you heard that. (Are you confusing it with Google having bought a D-Wave machine, years ago?) D-Wave is still around but had no role whatsoever in Willow as far as I know. 25. KP Says: Comment #25 December 10th, 2024 at 4:18 pm Link for Random Circuit Sampling does not work for me. Leave a Reply You can use rich HTML in comments! You can also use basic TeX, by enclosing it within $$ $$ for displayed equations or \( \) for inline equations. Comment Policies: After two decades of mostly-open comments, in July 2024 Shtetl-Optimized transitioned to the following policy: All comments are treated, by default, as personal missives to me, Scott Aaronson---with no expectation either that they'll appear on the blog or that I'll reply to them. At my leisure and discretion, and in consultation with the Shtetl-Optimized Committee of Guardians, I'll put on the blog a curated selection of comments that I judge to be particularly interesting or to move the topic forward, and I'll do my best to answer those. But it will be more like Letters to the Editor. Anyone who feels unjustly censored is welcome to the rest of the Internet. To the many who've asked me for this over the years, you're welcome! 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