https://scottaaronson.blog/?p=8669 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. --------------------------------------------------------------------- << Toward a non-constant cancellation function FAQ on Microsoft's topological qubit thing Q1. Did you see Microsoft's announcement? A. Yes, thanks, you can stop emailing to ask! Microsoft's Chetan Nayak was even kind enough to give me a personal briefing a few weeks ago. Yesterday I did a brief interview on this for the BBC's World Business Report, and I also commented for MIT Technology Review. Q2. What is a topological qubit? A. It's a special kind of qubit built using nonabelian anyons, which are excitations that can exist in a two-dimensional medium, behaving neither as fermions nor as bosons. The idea grew out of seminal work by Alexei Kitaev, Michael Freedman, and others starting in the late 1990s. Topological qubits have proved harder to create and control than ordinary qubits. Q3. Then why do people care about topological qubits? A. The dream is that they could eventually be more resilient to decoherence than regular qubits, since an error, in order to matter, needs to change the topology of how the nonabelian anyons are braided around each other. So you'd have some robustness built in to the physics of your system, rather than having to engineer it laboriously at the software level (via quantum fault-tolerance). Q4. Did Microsoft create the first topological qubit? A. Well, they say they did! [Update: Commenters point out to me that buried in Nature's review materials is the following striking passage: "The editorial team wishes to point out that the results in this manuscript do not represent evidence for the presence of Majorana zero modes in the reported devices. The work is published for introducing a device architecture that might enable fusion experiments using future Majorana zero modes." So, the situation is that Microsoft is unambiguously claiming to have created a topological qubit, and they just published a relevant paper in Nature , but their claim to have created a topological qubit has not yet been accepted by Nature's peer review.] Q5. Didn't Microsoft claim the experimental creation of Majorana zero modes--a building block of topological qubits--back in 2018, and didn't they then need to retract their claim? A. Yep. Certainly that history is making some experts cautious about the new claim. When I asked Chetan Nayak how confident I should be, his response was basically "look, we now have a topological qubit that's behaving fully as a qubit; how much more do people want?" Q6. Is this a big deal? A. If the claim stands, I'd say it would be a scientific milestone for the field of topological quantum computing and physics beyond. The number of topological qubits manipulated in a single experiment would then have finally increased from 0 to 1, and depending on how you define things, arguably a "new state of matter" would even have been created, one that doesn't appear in nature (but only in Nature). Q7. Is this useful? A. Not yet! If anyone claims that a single qubit, or even 30 qubits, are already useful for speeding up computation, you can ignore anything else that person says. (Certainly Microsoft makes no such claim.) On the question of what we believe quantum computers will or won't eventually be useful for, see like half the archives of this blog over the past twenty years. Q8. Does this announcement vindicate topological qubits as the way forward for quantum computing? A. Think of it this way. If Microsoft's claim stands, then topological qubits have finally reached some sort of parity with where more traditional qubits were 20-30 years ago. I.e., the non-topological approaches like superconducting, trapped-ion, and neutral-atom have an absolutely massive head start: there, Google, IBM, Quantinuum, QuEra, and other companies now routinely do experiments with dozens or even hundreds of entangled qubits, and thousands of two-qubit gates. Topological qubits can win if, and only if, they turn out to be so much more reliable that they leapfrog the earlier approaches--sort of like the transistor did to the vacuum tube and electromechanical relay. Whether that will happen is still an open question, to put it extremely mildly. Q9. Are there other major experimental efforts to build topological qubits? A. No, it's pretty much just Microsoft [added: apparently Nokia Bell Labs also has a smaller, quieter effort]. Purely as a scientist who likes to see things tried, I'm grateful that at least one player stuck with the topological approach even when it ended up being a long, painful slog. Q10. Is Microsoft now on track to scale to a million topological qubits in the next few years? A. In the world of corporate PR and pop-science headlines, sure, why not? As Bender from Futurama says, "I can guarantee anything you want!" In the world of reality, a "few years" certainly feels overly aggressive to me, but good luck to Microsoft and good luck to its competitors! I foresee exciting times ahead, provided we still have a functioning civilization in which to enjoy them. Email, RSS Follow This entry was posted on Thursday, February 20th, 2025 at 12:34 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. 20 Responses to "FAQ on Microsoft's topological qubit thing" 1. Ilyas Says: Comment #1 February 20th, 2025 at 4:43 am Scott - great post. Thanks. Just a small reminder - we published our work on non abelian Anyons in 2023. Exact same outcome in the sense of a topological qubit. Think of our gate fidelities as MSFT energy gap more to come on this from Quantinuum this year. This work sits alongside our more established QCCD architecture and our QEC work 2. Simon Burton Says: Comment #2 February 20th, 2025 at 5:00 am > one that doesn't appear in nature that we know of. 3. Mikael Johansson Says: Comment #3 February 20th, 2025 at 5:48 am Informative as always, many thanks! Regarding Q9, also Nokia Bell Labs is developing topological qubits, although from a somewhat different angle. https:// www.nokia.com/bell-labs/research/air-lab/data-and-devices/ topological-quantum-computing/ 4. Prasanna Says: Comment #4 February 20th, 2025 at 5:50 am Scott, Are there any in principle advantages for Topological qubits vs other approaches that give them a fundamental edge ? Yes, engineering them would be different story, however if we are sure they are better in a way that transistors were for vacuum tubes, then it would involve only redirecting engineering resources towards that approach ? 5. Danylo Yakymenko Says: Comment #5 February 20th, 2025 at 5:54 am Q11: How much resilience can they show with that single topological qubit? 6. Philip Reinhold Says: Comment #6 February 20th, 2025 at 6:25 am Seems to me that in order to claim that a qubit exists, you should have coherence times and some gates with fidelities. All I see in the paper is observed switching rates between two states under measurement. 7. Martin Says: Comment #7 February 20th, 2025 at 8:44 am Hello, first of all, I am not an expert and still learning QC. So please read me with the appropriate caution. I found someone online raising an interesting question: https:// www.reddit.com/r/QuantumComputing/comments/1ite220/ majorana_1_did_anyone_read_the_fine_print/ He quotes the editorial team: "The editorial team sought additional input from Reviewers #2 and #3 after the second round of review to establish this manuscript's technical correctness. Their responses proved satisfactory enough to proceed to publication. The editorial team wishes to point out that the results in this manuscript do not represent evidence for the presence of Majorana zero modes in the reported devices. The work is published for introducing a device architecture that might enable fusion experiments using future Majorana zero modes." It seems to me from reading the reports that the referees do not agree on the demonstration of a qubit's presence. From ref#1 (on first review): https://static-content.springer.com/esm/ art%3A10.1038%2Fs41586-024-08445-2/MediaObjects/ 41586_2024_8445_MOESM2_ESM.pdf "Here the authors seem to imply that in this manuscript a qubit (and its parity readout) is demonstrated, which is not true." And from the Nature publication (I add the link just to save you some time): https://www.nature.com/articles/s41586-024-08445-2 "1DTSs2,3,4 are a promising platform for building topological qubits." All these elements confuse me: On the one hand, I found online that their new chip had 8 qubits: https://www.techtarget.com/searchdatacenter/news/366619479/ Microsoft-unveils-quantum-chip-Majorana-1-for-future-advances #:~:text= Today%2C%20Majorana%201%20has%20only,said%20in%20a%20blog%20post. On the other hand, some referees from the peer review do not seem to acknowledge the presence of a qubit nor the proof of the existence of Majoranas. The majority of the referees still seem to recognize this work as being worthy of publication. My main confusion is that they seem to claim to have an 8-qubit chip while still discussing if even one has been made. Disclaimers: I mostly do not understand the physics involved. I have been a silent reader for the past few months and only have ~1 year of QC background. I have a simplified view of what is happening, and I am only asking for clarifications on things that appear to me as contradictory statements. I am not saying anything posted is wrong or sensationalist, I am just confused. Feel free to get rid of the disclaimer parts to keep the conversation structured on the blog 8. Vladimir Says: Comment #8 February 20th, 2025 at 8:54 am Philip Reinhold #6 > Seems to me that in order to claim that a qubit exists, you should have coherence times and some gates with fidelities ... and in order to claim that the qubit is based on topological Majorana modes, the coherence time should increase exponentially when temperature is decreased and when the length of the wire is increased. Interestingly, the paper itself makes a much more modest claim: "These measurements do not, by themselves, determine whether the low-energy states detected by interferometry are topological", and even Nature's editorial team isn't fully aboard the hype train this time: "The editorial team wishes to point out that the results in this manuscript do not represent evidence for the presence of Majorana zero modes in the reported devices" (though this sentence is hidden away in the peer review file). 9. Michael Vassar Says: Comment #9 February 20th, 2025 at 10:00 am If the claim holds up it sure sounds like a breakthrough to me. This sort of resilience was always the unachievable holy grail for QC so it seems a lot more likely to me that we get useful QC in a decade than it did a few days ago. 10. Curious Says: Comment #10 February 20th, 2025 at 10:15 am Hi Scott, I was surprised to hear that they were claiming they had a topological qubit... I thought this was some misinterpretation in the conversion from scientific result to science writing. But here the scientists are indeed claiming "yes, we have a topological qubit." That would be amazing, but it seems like not what's claimed in Nature? What do you make of this disclaimer in the peer review file (available here https:// static-content.springer.com/esm/ art%3A10.1038%2Fs41586-024-08445-2/MediaObjects/ 41586_2024_8445_MOESM2_ESM.pdf): "The editorial team wishes to point out that the results in this manuscript do not represent evidence for the presence of Majorana zero modes in the reported devices. The work is published for introducing a device architecture that might enable fusion experiments using future Majorana zero modes." So I guess my question is, if the qubit thing is not in the Nature paper, is it a claim we should be waiting on more results for? Seems like there's a disconnect somewhere. 11. Davide Castelvecchi Says: Comment #11 February 20th, 2025 at 10:30 am Hi Scott, I am a bit surprised that your post seems to have missed an opportunity to clarify what seems to be the most crucial point: Microsoft's claim to have created a topological qubit using two nanowires does not appear in their Nature paper, only in their press release. As far as I can tell (and despite how the news was reported by the New York Times, the Financial Times and probably countless other outlets), there are no qubits in the paper. 12. Nina Says: Comment #12 February 20th, 2025 at 10:34 am So did they do it or did they not? Did they find the Majoran particle or did they not? 13. Jim Sturtevant Says: Comment #13 February 20th, 2025 at 10:34 am @Mikael Johansson - to be run on a 5110 I hope 14. Esteban Riquelme Says: Comment #14 February 20th, 2025 at 10:52 am Why are topological qubits so difficult to create? Why does Microsoft continue to bet on topological qubits if other quantum computing technologies already exist? How likely is it that topological qubits will become the dominant technology in quantum computing? What does 'creating a new state of matter' with topological qubits imply? What impact would the creation of a single topological qubit have on quantum computing? 15. fernando Says: Comment #15 February 20th, 2025 at 11:28 am Hi Scott, did Chetan mention when/where they will report the data on their "topological qubit that's behaving fully as a qubit"? It's not in the Nature paper.... 16. Scott Says: Comment #16 February 20th, 2025 at 12:12 pm Ilyas #1: Thanks. I do want to maintain the distinction between creating nonabelian anyons "in software"--what Quantinuum did in 2023, by simulating the anyons in a system of trapped-ion qubits--and creating them "in hardware," which is what Microsoft claims to have done. 17. Scott Says: Comment #17 February 20th, 2025 at 12:15 pm Martin #7: Thanks!! I've added a note about that to the post. It's clear that Microsoft is claiming to have created both majorana zero modes and topological qubits. It's also clear that, if they once again haven't, they'll have egg all over their faces; I don't know if their topological QC effort could recover from two high-profile retracted claims. Beyond that, I certainly don't know any more than the device physicists do, and people should feel free to debate it here! 18. Olivier Ezratty Says: Comment #18 February 20th, 2025 at 12:15 pm Microsoft is not the only commercial player working on Majorana fermions. Nokia is also working in that field, although quietly. In Murray Hill, New Jersey. 19. Anyonimous Says: Comment #19 February 20th, 2025 at 1:53 pm So they created something and packaged it in a chip in 20 years that professional physicists working on particle colliders only identified experimental evidence of in recent years (https:// en.wikipedia.org/wiki/Anyon#Experiment)? Is this possible? 20. Ted Says: Comment #20 February 20th, 2025 at 3:04 pm How good are topological qubits at performing non-Clifford gate operations? Their device roadmap paper seems to focus almost entirely on implementing Clifford gates, but it says in passing that the T gate "is not a topologically-protected operation in Majorana-based qubits. However, a noisy implementation of the T gate together with low-noise Clifford operations can be used to distill low noise resource states from which fault-tolerant T gates can be implemented ... Going beyond Clifford operations to obtain a computationally universal gate set requires additional, non-topologically-protected operations, [which] are not the focus of this paper." Are they sweeping a potentially big issue under the rug here? Or are they correct in their implication that protecting non-Clifford gate operations isn't that big of a deal? Does the additional overhead required for protecting non-Clifford gates risk negating most of the advantage of the topological protection of the Clifford gates? 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. 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