[HN Gopher] Two-qubit silicon quantum processor with operation f...
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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
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