[twtw]

... and couldn't get the correct answers for LiH. Interesting that the article didn't mention this.

From the paper:

> For lithium hydride, LiH, we were not able to reproduce closely the ground state energy with the currently available hardware. When accounting for 3 orbitals and using a scaling factor of r = 4, we already had to use 1558 qubits, which is a large fraction of available qubits. To summarize: the investigated method in general works, but it might be difficult to apply it to larger systems.

[jf-]

Presumably because that’s just a matter of scale. The calculation didn’t turn out wrong, the machine just isn’t powerful enough to calculate it. All of this work is proof of concept for more powerful devices down the road, the point isn’t that it’s better than a classical computer right now.

[twtw]

Right, and the paper itself is very upfront about that. I don't have any objection to the research, which is likely very valuable, but I do find it strange that the article claims they solved two problems without mentioning that only one of the solutions was correct.

It would be great if the article said they solved one and made good progress on techniques for the second that will likely work on next generation hardware, but the article didn't say that. I don't see how it being a matter of scale makes this acceptable. It's like the U.S. national labs unveiling the world's first exaflop supercomputer, with a footnote indicating that in fact the computer is only 100 petaflops at the moment.

[KKKKkkkk1]

> It's like the U.S. national labs unveiling the world's first exaflop supercomputer, with a footnote indicating that in fact the computer is only 100 petaflops at the moment.

Can you add context?

[jcranmer]

This is referring to the Summit supercomputer announcement a few months ago.

Measuring the speed of a supercomputer is difficult because there are several factors that control performance that affect benchmarks very differently. The most common benchmark in use is LINPACK, which measures how long it takes the computer to solve an appropriately large matrix equation Ax = b and then computes how many floating-point operations such an equation notionally takes. This has been criticized for various reasons, but it's what TOP500 measures.

Summit scored 143 PFLOPS on this metric. However, the press release called it a exascale supercomputer because it can issue 1 quadrillion instructions per second, so 1 exaop. To most people in the industry, the goal of exascale meant 1 EFLOP on LINPACK, so it really does come across as saying "We built a 1 EFLOP computer (footnote: only 143 PFLOPS)."

[williamscales]

Is there any evidence it will ever be better than a classical computer?

[krastanov]

There is no evidence that quantum annealing (what D-Wave does) is any better than classical computers.

There is a lot of evidence that quantum computers (the gate model) or, equivalently, quantum adiabatic computing is better than classical computing. All of it is based on a family of conjectures about the complexity classes P, BQP, and NP.

Scott Aaronson's blog is one of my go-to suggestions for rigorous introduction to the topic.

[FeepingCreature]

For the record, the concept is called Quantum Supremacy [1]. So far, there is no demonstration of quantum supremacy, but it seems like it may just be a matter of time.

[1] https://en.wikipedia.org/wiki/Quantum_supremacy

[throwawaymath]

Quantum supremacy is not merely about quantum computers performing tasks better than classical computers. It's about quantum computers achieving a superpolynomial speedup over classical computers, such that classical computers can't feasibly perform the task in a reasonable amount of time for all inputs.

That's an important distinction because it's significantly more difficult to achieve a fundamental asymptotic improvement instead of an iterative speedup for the same factor. If a quantum computer completes a task with complexity O(2n) that a classical computer requires O(10n) to complete, you don't have quantum supremacy. If your quantum computer can accomplish a task in O(2n) that your classical computer needs O(2^n) to perform, you've got supremacy.

Given that nuance, I wouldn't say it may be a matter of time before we demonstrate quantum supremacy. There is still an undercurrent of skepticism in the research community.

[stochastic_monk]

It’s related, but quantum supremacy is about asymptotic speedups rather than actual speed differences.

Additionally, it’s worth keeping in mind that D-Wave machines aren’t true quantum computers in the sense that they can’t perform Grover’s or Shor’s algorithms.

[garmaine]

It’s not clear what “true quantum computer” means. There are many different types of quantum computers, and quantum annealing, what D-wave does, is one. It’s just the least interesting of the bunch...

[steve_musk]

Well scaling is the problem when dealing with quantum chemistry.