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A Reality Check on Quantum Computers

wsj.com

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Re: A Reality Check on Quantum Computers

#21

Post by ahelwer »

The_rationalist wrote: post #19
Tyr42 wrote: post #17

Earlier quoted context omitted.

There's a lot of research at the "P = BQP?", "NP I can tell you that Shor's algorithm for factoring takes O((log n)^2 (log log n)(log log log n)) (we can round that up to O((log n)^4) if you want) to a the best known classical algorithm of O(exp(1.9 * (log n)^(1/3) (log log n)^(2/3))) But unless I tell you how fast each gate is, that tells you nothing about the constant time factors. Also, all these quantum algorithm…

But could quantum computing accelerate AI workloads such as graph traversal/rewriting? Iff quantum computing is only useful at breaking encryption, I don't see the point in funding quantum computing research.

Getting an exponential speedup on simulating quantum-mechanical systems (protein folding/binding, material design) is the killer app of quantum computing. Nobody is funding quantum computers because they want to break public-key crypto; that's just a somewhat unfortunate (though interesting) side-effect bringing a bunch of costs with cryptographic R&D plus transitioning systems to post-quantum crypto.

Quantum computing is not expected to have large impacts on machine learning at this time after Ewin Tang's paper. There's an especially large amount of fluff in this area, though.

Re: A Reality Check on Quantum Computers

#22

Post by l33tman »

abdullahkhalids wrote: post #8

> The most profound issue, however, concerns the meaning of quantum supremacy. After all, it doesn’t take qubits to solve important quantitative problems faster than any classical computer. Any carbon atom can “calculate” the solution of a very important practical problem—how does carbon behave?—simply by doing its thing. The author [1] is trivializes the notion of computational machine. Calculating using a classical…

There are a lot of interesting applications that doesn't require a "computational machine".. While the carbon atom example seems excessively specific, there are other setups like D-Waves quantum computer that works in a sort of in-between way, with programmable links between "atoms" so you can setup a custom Hamiltonian that should be minimized by the computer.

That way you get sort of the best by both worlds, you get a (limited) programmability and you get easier observations than you would have access to just by for example designing a molecule encapsulating the problem you want to solve, as you would have to observe it "doing its stuff" somehow.

Just because it can't crack crypto doesn't mean a large-scale version of a setup like this can't be valuable. The field of quantum chemistry needs to use huge supercomputer clusters to simulate stuff like this.

Re: A Reality Check on Quantum Computers

#23

Post by fixf »

false-mirror wrote: post #14

I'm disappointed that this article doesn't answer my only real question about quantum computers: What does a reasonable expectation look like? What is the range of potential performance gains? I understand that this is the frontier and no one has any definite answers, but I hear everything from "trivial" improvements to "insta-crack AES-256" (thousands of trillion trillion trillion trillions times faster). Does anyon…

There's multiple bounds. The mounting evidence for BPP=BQP unfortunately falls aside P=BPP for evidence without proof. The weak interpretation is that BQP is vulnerable, and the strong interpretation is that BQP is broken. It's in the air, but for certain applications people can't afford to guess wrong. It's reasonable to remove it as a dependency in those fields.

Re: A Reality Check on Quantum Computers

#25

Post by nestorD »

ahelwer wrote: post #20
false-mirror wrote: post #14

I'm disappointed that this article doesn't answer my only real question about quantum computers: What does a reasonable expectation look like? What is the range of potential performance gains? I understand that this is the frontier and no one has any definite answers, but I hear everything from "trivial" improvements to "insta-crack AES-256" (thousands of trillion trillion trillion trillions times faster). Does anyon…

Quantum computers won't insta-crack AES. They only give a square-root speedup for symmetric crypto (so you can double the key length for equivalent security) with Grover's algorithm. It's public-key crypto algorithms based on prime factorization or the descrete log problem which will be broken by Shor's. However, running Shor's algorithm on production key sizes requires a huge quantum computer (with millions of qbits…

This.

Quantum computing have be designed to solve a single problem : the simulation of quantum systems on a classical computer is very slow, lets build a quantum computer so that it will be fast.

It might seem like a fringe use case but it matters (a lot) to industrials and researchers in a wide variety of topics.

Re: A Reality Check on Quantum Computers

#26

Post by deusofnull »

barbecue_sauce wrote: post #24
mathattack wrote: post #18

I’ve noticed that the MBA crowd (including some friends!) who jumped into the Bitcoing bandwagon at 10K are now hawking Quantum Computing.

How does one hawk Quantum Computing?

I very much want to make a stephen hawkings pun but i guess technically he wasnt a quantum computing guy, but damn close

Re: A Reality Check on Quantum Computers

#27

Post by PeterisP »

abdullahkhalids wrote: post #8

> The most profound issue, however, concerns the meaning of quantum supremacy. After all, it doesn’t take qubits to solve important quantitative problems faster than any classical computer. Any carbon atom can “calculate” the solution of a very important practical problem—how does carbon behave?—simply by doing its thing. The author [1] is trivializes the notion of computational machine. Calculating using a classical…

The first aspect that you mention is actually not a disagreement but the whole point of his message - the recently popularized demonstrations of "quantum supremacy" did not allow for universal programmability, but instead were more comparable to an experimental setup for a particular problem of how do atoms behave in that setup.

Having a proper quantum computer with enough fully programmable bits to demonstrate quantum supremacy would be valuable, but (as the author states) the meaning of quantum supremacy is tricky, and we currently have achieved "quantum supremacy" only if we use a very limited, "cheating" definition of quantum supremacy.

Re: A Reality Check on Quantum Computers

#28

Post by LeftHandPath »

barbecue_sauce wrote: post #24
mathattack wrote: post #18

I’ve noticed that the MBA crowd (including some friends!) who jumped into the Bitcoing bandwagon at 10K are now hawking Quantum Computing.

How does one hawk Quantum Computing?

People riding the bandwagon and generally talking about it like they're in on it when they don't know what a qubit or bell state is (or how to read braket notation).

It's a similar line to AI - if the people talk about it like it has the potential to (and eventually will) destroy the world, they probably don't know much about it (in that case they're conflating sentience with intelligence, and ignoring the word "artificial).

The people who are working on it right now will - like with AI - tell you that it's in its infancy, that its current applications are more limited than they are made to appear in pop-culture, and that (generally) things are harder and take longer than people pretend.

Which is exactly what the author of the WSJ article is getting at (because he's not a hawker - he knows):

> "There’s little doubt that, in the long run, computers that exploit quantum features of matter will dramatically enhance our ability to address useful problems. But we’re not there yet, nor is success guaranteed. For the foreseeable future we will have, at best, a “quantum advantage” in well-chosen applications, not “quantum supremacy” along a broad front."

Re: A Reality Check on Quantum Computers

#29

Post by PeterisP »

false-mirror wrote: post #14

I'm disappointed that this article doesn't answer my only real question about quantum computers: What does a reasonable expectation look like? What is the range of potential performance gains? I understand that this is the frontier and no one has any definite answers, but I hear everything from "trivial" improvements to "insta-crack AES-256" (thousands of trillion trillion trillion trillions times faster). Does anyon…

For most problems, no performance gains whatsoever. There's no expection for quantum computers to replace or improve general computing.

You can get immense speedups for a very particular set of problems, turning them from "can't possibly complete ever" to solvable; so it would be like an assistive device for these niche tasks, but it would be very important for them because otherwise they're not really practical to solve.

Re: A Reality Check on Quantum Computers

#30

Post by mathattack »

barbecue_sauce wrote: post #24
mathattack wrote: post #18

I’ve noticed that the MBA crowd (including some friends!) who jumped into the Bitcoing bandwagon at 10K are now hawking Quantum Computing.

How does one hawk Quantum Computing?

Starting a consulting company to help companies “leverage this transformational game changing innovation opportunity.”
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