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Comment by Aardwolf | Hacker News Reader

Once quantum computers are possible, is there actually anything else, any other real world applications, besides breaking crypto and number theory problems that they can do, and do much better than regular computers?

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Yes, in fact they might be useful for chemistry simulation long before they are useful for cryptography. Simulations of quantum systems inherently scale better on quantum hardware.

https://en.wikipedia.org/wiki/Quantum_computational_chemistr...

More recently it's turned out that quantum computers are less useful for molecular simulation than previously thought. See: https://www.youtube.com/watch?v=pDj1QhPOVBo

The video is essentially an argument from the software side (ironically she thinks the hardware side is going pretty well). Even if the hardware wasn't so hard to build or scale, there are surprisingly few problems where quantum algorithms have turned out to be useful.

It is tough to beat classical computers. They work really well, and a huge amount of time (including some of mine) has gone into developing fast algorithms for them to do things they're not naturally fast at, such as quantum chemistry.

At 15:00, she says "quantum computers are surprisingly good at [...] quantum simulations [of electron behavior]", which would seem to contradict you.

One theoretical use case is “Harvest Now, Decrypt Later” (HNDL) attacks, or “Store Now, Decrypt Later” (SNDL). If an oppressive regime saves encrypted messages now, they can decrypt later when QCs can break RSA and ECC.

It's a good reason to implement post-quantum cryptography.

Wasn't sure if you meant crypto (btc) or cryptography :)

I will never get used to ECC meaning "Error Correcting Code" or "Elliptic Curve Cryptography." That said, this isn't unique to quantum expectations. Faster classical computers or better classical techniques could make various problems easier in the future.

What do you want it to mean?

I think he meant Error Correcting Code (just this, not this "or" ECCrypto)

From TFA: ‘One more time for those in the back: the main known applications of quantum computers remain (1) the simulation of quantum physics and chemistry themselves, (2) breaking a lot of currently deployed cryptography, and (3) eventually, achieving some modest benefits for optimization, machine learning, and other areas (but it will probably be a while before those modest benefits win out in practice). To be sure, the detailed list of quantum speedups expands over time (as new quantum algorithms get discovered) and also contracts over time (as some of the quantum algorithms get dequantized). But the list of known applications “from 30,000 feet” remains fairly close to what it was a quarter century ago, after you hack away the dense thickets of obfuscation and hype.’

It turns out they're not so useful for chemistry. https://www.youtube.com/watch?v=pDj1QhPOVBo

I believe the primary most practical use would be compression. Devices could have quantum decoder chips that give us massive compression gains which could also massively expand storage capacity. Even modest chips far before the realization of the scale necessary for cryptography breaking could give compression gains on the order of 100 to 1000x. IMO that's the real game changer. The theoretical modeling and cryptography breaking that you see papers being published on is much further out. The real work that isn't being publicized because of the importance of trade secrets is on storage / compression.

> compression gains on the order of 100 to 1000x.

This feels like woo-woo to me.

Suppose you're compressing the text of a book: How would a quantum processor let you get a much better compression ratio, even in theory?

If you're mistakenly describing the density of information on some kind of physical object, that's not data compression, that's just a different storage medium.

Pretty sure quantum algorithms can't be used for compression.

Someone just has to figure out how to actually implement middle out compression on a quantum computer.

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