Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Scott’s Supreme Quantum Supremacy FAQ

scottaaronson.com

Post reply on HN
Print view View original

51–60 of 215 posts

Re: Scott’s Supreme Quantum Supremacy FAQ

#51

Post by galaxyLogic »

3PS wrote: post #32
nexuist wrote: post #2

Preface: I know nothing about quantum computing. What exactly is a qubit? I'm not asking what does it mean, because I know there's superpositions and all that jazz, but as in...like, in an electronic circuit, what is a qubit? Is it made out of logic gates? Which ones? If we can make one qubit, can't we just make a bunch of them by copy and pasting circuits similar to how we used vacuum tubes in the 60s and 70s? How c…

Short answer, a qubit is a unit vector in a 2D complex Hilbert space. Now, that doesn't actually say much about why we care or how they're useful. In practical terms, you can think of qubits as complex unit vectors along two axes, with one axis corresponding to |0⟩ (the zero qubit) and one axis corresponding to |1⟩, or the one qubit. So for example, you could have a qubit called |+⟩, which is just shorthand for (|0⟩…

> Schrödinger's cat must be alive or dead once we open the box

I recently had a conversation about this in another thread. It seems to me, and nobody tried to convince me otherwise, that the Cat would be the Observer. Therefore it would be dead, NOT dead AND alive, as soon as it observes the poisonous gas in its box.

Re: Scott’s Supreme Quantum Supremacy FAQ

#52

Post by daxfohl »

What's e.g. China and Russia doing in this space? Or the US Gov't for that matter? I can't imagine that national governments are just waiting for Google and IBM to do the research and publish their results. Is it possible/likely that NSA or some other national equivalent is way beyond these results already?

Re: Scott’s Supreme Quantum Supremacy FAQ

#53

Post by bjornsing »

rsln-s wrote: post #47
bjornsing wrote: post #45

I have the greatest respect for Scott, but I do think he’s being a bit too enthusiastic here in comparison with the D-wave. At the very least I think he should have included this question in his list: Q: Why can the D-wave not be used to illustrate “quantum supremacy” in a similar way? (As I understand it the D-wave can sample from the solutions to ”ising model-like” problems, which I assume would be extremely diffic…

Unfortunately, the same complexity considerations do not hold for Ising problems. While many NP-hard problems can be formulated in Ising form, it is often not hard to get a “pretty good” solutions to these problems. DWave and collaborators have spent a decade trying to come up with exactly the same thing as demonstrated here — namely, a problem specifically designed to demonstrate quantum advantage of any sort — and…

I’m aware of D-wave’s struggles, but my impression was that they had failed at finding a “deterministic” problem where they could show quantum advantage. I’ve never heard a claim that whatever probability distribution the D-wave can sample from a classical computer can also sample from. I’d love to read about it if you have a reference!

Re: Scott’s Supreme Quantum Supremacy FAQ

#54

Post by reilly3000 »

daxfohl wrote: post #52

What's e.g. China and Russia doing in this space? Or the US Gov't for that matter? I can't imagine that national governments are just waiting for Google and IBM to do the research and publish their results. Is it possible/likely that NSA or some other national equivalent is way beyond these results already?

I don't know what the NSA spends on R&D, but I have to imagine they don't have a multi-billion dollar budget for secret R&D facilities and talent. It would seem more likely they are monitoring developments in public and private research and responding opportunistically. I'm just making assumptions here, but also I don't think somebody with clearance could correct me here in public :P

Re: Scott’s Supreme Quantum Supremacy FAQ

#55

Post by itcrowd »

tagrun wrote: post #43
itcrowd wrote: post #25

Earlier quoted context omitted.

Essentially, they use superconducting electronics to create a quantum circuit. It's not the same logic gates as a traditional computer chip and not based on the same physics. The details are difficult & messy. There are several reasons it doesn't scale easily to more qubits, but you can imagine that you don't want the chip to be large (must be cooled to 25mK!) but the qubits should be spaced quite far apart so they d…

We do want the chip to be "large" eventually. The scalability doesn't have anything with those, however. Refrigerators are pretty large and these devices are really really tiny; also qubits shouldn't be spaced "far" apart, this would kill all the (controllable) couplings.

I was a little too fast and loose in my previous post. You are correct that we want a large [number of qubits] on a chip eventually. The chips are tiny and the fridges large enough for now (50 qubits). It's not clear to me that they can handle thousands of qubits as imagined. The cryostat will undoubtedly be able to house the chip, but the extra electronics / cables must run in there as well. With 1000 qubits and 2 cables per qubit this will be a major challenge.

You are correct about the coupling of the qubits, I was simplifying too strongly there.

I do stand by my scaling point (center qubits harder to reach) but I'm open for counter arguments.

Thanks.

Re: Scott’s Supreme Quantum Supremacy FAQ

#56

Post by bjornsing »

bjornsing wrote: post #45

I have the greatest respect for Scott, but I do think he’s being a bit too enthusiastic here in comparison with the D-wave. At the very least I think he should have included this question in his list: Q: Why can the D-wave not be used to illustrate “quantum supremacy” in a similar way? (As I understand it the D-wave can sample from the solutions to ”ising model-like” problems, which I assume would be extremely diffic…

Another reason I feel this is oversold: This quantum “computer” cannot run Shores factorization algorithm. But if it could it would only be able to factor integers up to 2^53. The time required to factor a 2^60 to 2^80 integer on a classical computer is measured in milliseconds [1]...

Quantum supremacy in any reasonable sense of the word supremacy is a long way off.

1. https://hal.inria.fr/file/index/docid/451604/filename/smalli...

Re: Scott’s Supreme Quantum Supremacy FAQ

#57

Post by dcposch »

bjornsing wrote: post #56
bjornsing wrote: post #45

I have the greatest respect for Scott, but I do think he’s being a bit too enthusiastic here in comparison with the D-wave. At the very least I think he should have included this question in his list: Q: Why can the D-wave not be used to illustrate “quantum supremacy” in a similar way? (As I understand it the D-wave can sample from the solutions to ”ising model-like” problems, which I assume would be extremely diffic…

Another reason I feel this is oversold: This quantum “computer” cannot run Shores factorization algorithm. But if it could it would only be able to factor integers up to 2^53. The time required to factor a 2^60 to 2^80 integer on a classical computer is measured in milliseconds [1]... Quantum supremacy in any reasonable sense of the word supremacy is a long way off. 1. https://hal.inria.fr/file/index/docid/451604/fil…

The claim here is that they're about to demonstrate QC on a specific hard sampling problem , where one small quantum computer will produce a result in minutes that takes a months on a big cluster of classical computers.

That is still clearly quantum supremacy, even if Shor's algorithm is not yet implementable.

Re: Scott’s Supreme Quantum Supremacy FAQ

#58

Post by gowld »

whatshisface wrote: post #4

If it goes well, the history of quantum computing will be divided up in to three eras: the era of twisty philosophical arguments that it's working ("the molecule is simulating itself"), the era of academic arguments that it's working ("we can solve this one carefully constructed problem") and the era of practical arguments ("Amazon is selling QC time for $20/kilogate-bit, what do you mean it's not possible?"). Quantu…

What are the theoretical models for the energy cost of computing on a qubit? I'll be excited for QC when there is known way (even with some handwaving and future-tech plans) to compute a non-trivial result for a reasonable sum, such as "crack someone's private RSA key for under $10M of compute cost"

Re: Scott’s Supreme Quantum Supremacy FAQ

#59

Post by dcposch »

calhoun137 wrote: post #49

I think we need to comes to grips with a hard truth about the reality of academic life. Once you invest decades of your life into a research subject, if it turns out the entire thing is never going to work, there are major social and financial pressures to deceive the public about the true nature of the subject. I saw this happen with string theory first hand, and my experience with string theory was a major factor t…

> Once you invest decades of your life into a research subject, if it turns out the entire thing is never going to work, there are major social and financial pressures to deceive the public about the true nature of the subject.

You're implying that Scott Aaronson is being deceptive.

I think that needs better evidence. The story you linked to is two years old and it's about QC skeptic Gil Kalai.

Scott addresses him directly in his post:

> If quantum supremacy was achieved, what would it mean for the QC skeptics?

> I wouldn’t want to be them right now! They could of course retreat to the position that of course quantum supremacy is possible (who ever claimed that it wasn’t??), that the real issue has always been quantum error-correction. And indeed, some of them have consistently maintained that position all along. But others, including my good friend Gil Kalai, are on record, right here on this blog predicting that even quantum supremacy can never be achieved for fundamental reasons. I won’t let them wiggle out of it now.

Re: Scott’s Supreme Quantum Supremacy FAQ

#60

Post by sanxiyn »

bjornsing wrote: post #45

I have the greatest respect for Scott, but I do think he’s being a bit too enthusiastic here in comparison with the D-wave. At the very least I think he should have included this question in his list: Q: Why can the D-wave not be used to illustrate “quantum supremacy” in a similar way? (As I understand it the D-wave can sample from the solutions to ”ising model-like” problems, which I assume would be extremely diffic…

In principle, there is no reason why D-wave also can't achieve quantum supremacy. It is just that D-wave hasn't, so far.

As for Ising model, D-wave didn't outperform classical algorithm after classical algorithm was tuned (it was a new problem, so existing classical algorithm wasn't the best possible), see https://arxiv.org/abs/1401.1084, also there are reasons to suspect why Ising model will not provide any quantum speedup, see https://arxiv.org/abs/1411.5693.

Post reply on HN