[HN Gopher] Two-qubit silicon quantum processor with operation f... ___________________________________________________________________ Two-qubit silicon quantum processor with operation fidelity exceeding 99% Author : sizzle Score : 71 points Date : 2022-04-15 18:53 UTC (4 hours ago) (HTM) web link (www.science.org) (TXT) w3m dump (www.science.org) | tines wrote: | 99% doesn't seem very high. Does that mean that if you do 100 | operations, 1 of them will fail? | klodolph wrote: | The "Quantum threshold theorem" is what you care about here: | | https://en.wikipedia.org/wiki/Quantum_threshold_theorem | | Basically, if the error rate on an individual gate is low | enough, you can use the gate to construct larger (less | efficient) gates with arbitrarily low amounts of error. 99%, as | you say, is a bit low and you'd need impractically large | circuits to use these gates. | | You want error correction with classical computers too, it just | works differently. | fsh wrote: | Regular CPUs don't have error correction. The logic gates | simply don't make mistakes, even after trillions of | operations. The reason is that the gates are digital. | Manufacturing imperfections and noise don't matter, as long | as the signal levels stay within their bounds. | | On the other hand, current quantum computers are analog. Each | quantum gate will get the coefficients of its output states a | little bit wrong, and after a few tens of operations only | noise is left in the qubits. In principle, quantum error | correction could be used to measure and compensate for these | errors. But none of the technologies demonstrated so far are | anywhere near good enough for this. | version_five wrote: | Not my area but you hear about but flips due to cosmic | rays, and I've heard of mainframes that run everything on | two cpus as a form or error correction. I think your point | stands, just pointing out that there are occasional errors | in cpus | anonymousiam wrote: | SEUs are more of a problem in space. CPUs used for space | missions mitigate the errors in a few different ways. In | the past, the feature size on the CPU substrate was large | enough to absorb most cosmic radiation without incident. As | the feature sizes have shrunk and the old foundries are no | longer producing the old chips, many missions have adopted | "multiple voting" architectures. Satellites often use | "triple voted" processors. The Space Shuttle had a system | with five votes. | | I'm not a quantum computing expert, but I wonder if a SEU | would even matter in some parts of a quantum system. The | bits are in an undefined state during operation anyway. | klodolph wrote: | > The logic gates simply don't make mistakes, even after | trillions of operations. | | The error rates are _not zero._ Low, but not zero. | Trillions of operations is what, a split-second of runtime | on a five-year-old GPU? | | "High-reliability" systems invariably use some form of | error correction or error detection. You can do this at | different levels of abstraction. At a low level, you can | build redundant gates. At a company I used to work for, | this was a product we sold--it would synthesize ICs from an | HDL and incorporate error correction. (This particular | feature forced the company to get ITAR export licenses.) At | a different company I worked for, we did our error | correction at a high level using software. We encountered | hardware errors on a regular basis. I'm not even talking | about ECC--I'm talking about CPU errors. | | The only reason why you can think that imperfections and | noise don't matter is because there isn't much noise in | your environment and you aren't dealing with enough data | that you'll notice any errors. | | Deal with a large enough amount of data, enough CPUs, | enough RAM, and error becomes a certainty. | | The "quantum computers are analog" line is at best | profoundly misleading. If your definition of "analog" | extends to quantum computers, then I'd say that digital | computers are _also_ analog. Which is not an incorrect | thing to say. | sva_ wrote: | Consider your 2-bit RSA keys to be 99% compromised. | rafale wrote: | If you could reduce the search space by 99%, it will still be | too large. | zauguin wrote: | If you reduce the search space of 2 bit keys by 99% then | there there are only 0.04 keys left. That's too small to find | a single key, not too large. | alpineidyll3 wrote: | Assuming the logic is gate free lol. For real to call two | qubits a 'processor' has to be a new low. These reviewers | should be in science prison. | [deleted] | DebtDeflation wrote: | Is it able to factor 21 without precompilation and other tricks? | upofadown wrote: | Those are physical bits. It is nowhere close to even a single | logical bit that could do stuff like that. They are showing us | what they can do. Now someone has to figure out how to turn it | into something practical. | | I think the current goal is the factorization of 15. There is | no reason to suggest insane levels of challenge like 21. | metadat wrote: | I can't tell if parent is serious or joking. | fsh wrote: | Only if they figure out how to encode 21 with two bits. | messe wrote: | That's trivial[1]: 11 = 21 10 = 7 | 01 = 3 00 = FileNotFound | | [1]: https://thedailywtf.com/articles/What_Is_Truth_0x3f_ | bdamm wrote: | I know you're joking, but, this is not how Shor's algorithm | works. | awillen wrote: | Third on the front page and no comments about how this is a total | misrepresentation and/or a huge leap? C'mon folks - this is where | I come for due diligence on these kinds of things. | [deleted] | nh23423fefe wrote: | Spam, for want of content, is no virtue. | awillen wrote: | This begs the age-old question - whose content is less | valuable: the person who posts the substanceless comment or | the person who replies to it with an equally substanceless | comment pointing out that it's a substanceless comment? | Ethicists may never come to a consensus (at least not until | they can agree on who's worse between the person who ccs a | huge number of people who should be bcced or the person who | replies all saying that they should have bcced everyone and | asking everyone not to reply all). | lcnPylGDnU4H9OF wrote: | Maybe they're both undesirable. | moralestapia wrote: | Good leap forward but much more than 99% is needed, at least | 5-6 nines. | | Thing is that, as you add more qubits, "operation fidelity" (as | they call it) goes down exponentially, maybe even | superexponentially (?), so it's very hard to keep it within an | acceptable range on larger systems. | pyinstallwoes wrote: | So is quantum uncertainty a feature or a bug? | ryneandal wrote: | Yes. | pyinstallwoes wrote: | Neither a feature or a bug, nor not a feature or a bug. | ct520 wrote: | gave me a chuckle. Thank you for the summary and | commentary. | awillen wrote: | That is a helpful summary - thanks! | grungegun wrote: | False, except for a naive implementation, see: | https://en.wikipedia.org/wiki/Quantum_threshold_theorem | | If you look at the theorem, it is definitely sub-exponential | in the number of qubits needed to correct for error. | moralestapia wrote: | Sure, _in theory_ , in practice there's all sort of | physical constraints on the hardware that add/depend on | each other and whose complexity "grows" (I'm abusing the | term, I know) much faster than linear, hence why I used the | term exponential. | | _" Quantum mechanical states are extremely fragile and | require near absolute isolation from the environment. Such | conditions are hard to create and typically require | temperatures near absolute zero and shielding from | radiation. Thus, building quantum computers is expensive | and difficult. The challenge increases dramatically with | increasing size (number of qubits and the length of time | they must be coherent) and thus only small to medium scale | computers have been built so far."_, from [1]. Also, I | recommend reading out the whole article as it gives a nice, | broad, overview of the challenges in place, it's not as | easy as putting 1 qubit + 1 qubit together. | | 1: Quantum Computing: An Overview Across the System Stack, | https://arxiv.org/pdf/1905.07240.pdf ___________________________________________________________________ (page generated 2022-04-15 23:00 UTC)