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Is there a generally accepted crossover point where quantum computers will start outperforming classical computers on the same tasks? I was under the impression

Is there a generally accepted crossover point where quantum computers will start outperforming classical computers on the same tasks? I was under the impression it was somewhere around 100 qubits, but I'm sure there are caveats around noise and stability as well, not just number of qubits.

LeonM 7y ago
This threshold is commonly referred to as quantum supremacy. It could be that IBM just passed that threshold, but I'm by no means an expert on this. https://en.wikipedia.org/wiki/Quantum_supremacy https://en.wikipedia.org/wiki/Quantum_supremacy
- zamalek 7y ago
  > It could be that IBM just passed that threshold I don't think they have just yet. There is a simulated QC on conventional hardware with around 50 qbits. We are close, though, it might still happen this year.
  - reikonomusha 7y ago
    But even with 50 qubits, the amount of time per operation—if simulated classically—is at least a million+ times slower than what it would be for a quantum computer. This is like comparing disk to L1 cache. Does that count for supremacy? Mathematically, no. Does it count for some kind of advantage? Yes.
LanceH 7y ago
That point in time is, "tomorrow".
- just_one_time_ 7y ago
  Better to be safe, I always say 6-9 months away, at MOST.
The_rationalist 7y ago
It should be at least more like 10000 according to this paper https://arxiv.org/abs/1805.05224 https://arxiv.org/abs/1805.05224 But this is in an utopian world where we neglect quantum error correction and stability and the fact that quantum computers are mostly non programmable (there's not even one qubit logic gate..) TLDR quantum computing is going nowhere (excluding the low probability of a breakthrough in the field)
- q_eng_anon 7y ago
  'non-programmable'... um what?
WhitneyLand 7y ago
Here's why IBM says quantum supremacy is not relevant https://www.quantamagazine.org/quantum-supremacy-is-coming-heres-what-you-should-know-20190718 https://www.quantamagazine.org/quantum-supremacy-is-coming-h... From the article Quantum supremacy, we don’t use [the term] at all, said Robert Sutor, the executive in charge of IBM’s quantum computing strategy. We don’t care about it at all. The article also mentions practical considerations such as "quantum advantage", fault tolerance, and other initiatives competing with IbM. Relevant https://wikipedia.org/wiki/Quantum_supremacy https://wikipedia.org/wiki/Quantum_supremacy https://medium.com/@jackkrupansky/what-is-quantum-advantage-and-what-is-quantum-supremacy-3e63d7c18f5b https://medium.com/@jackkrupansky/what-is-quantum-advantage-...
- The_rationalist 7y ago
  The only real usefulness of quantum computers would be the supposed quantum supremacy. IBM not caring about Q supremacy is pure nonsense.
  - _red 7y ago
    >would be the supposed quantum supremacy True. Another way he could have responded is: We don't care if quantum computers actually do anything useful, only that we can use the PR to get positive stock price movement.
    - jeffdavis 7y ago
      They could also say "We are scientists doing cool stuff, discovering things, and having fun. Maybe it will be useful someday but we aren't really focusing on that." Why are you attributing some kind of cynical motive?
      - pessimizer 7y ago
        Because it is a job, not a hobby, and is essentially about money. It's not cynical to ascribe venal motivations to employment, and to imply it is is a cheap shot.
WilliamEdward 7y ago
Quantum supremacy is usually misunderstood, and it's likely quantum computers will not surpass transistor computers in every way; they will be much better at a subset of tasks only.
- quotemstr 7y ago
  Right. And the "quantum computer" won't ever really exist anyway: we'll just end up with quantum functional units on regular computers. We attach GPUs and TPUs to regular CPUs, but we don't call the resulting machines "graphics computers" or "tensor computers".
  - ineedasername 7y ago
    Actually, the term "graphics workstation" isn't uncommon, and "gaming rig" is a very common term for machines with great big GPUs attached.

LeonM 7y ago

This threshold is commonly referred to as quantum supremacy. It could be that IBM just passed that threshold, but I'm by no means an expert on this. https://en.wikipedia.org/wiki/Quantum_supremacy https://en.wikipedia.org/wiki/Quantum_supremacy

zamalek 7y ago
> It could be that IBM just passed that threshold I don't think they have just yet. There is a simulated QC on conventional hardware with around 50 qbits. We are close, though, it might still happen this year.
- reikonomusha 7y ago
  But even with 50 qubits, the amount of time per operation—if simulated classically—is at least a million+ times slower than what it would be for a quantum computer. This is like comparing disk to L1 cache. Does that count for supremacy? Mathematically, no. Does it count for some kind of advantage? Yes.

LanceH 7y ago

That point in time is, "tomorrow".

just_one_time_ 7y ago
Better to be safe, I always say 6-9 months away, at MOST.

The_rationalist 7y ago

It should be at least more like 10000 according to this paper https://arxiv.org/abs/1805.05224 https://arxiv.org/abs/1805.05224 But this is in an utopian world where we neglect quantum error correction and stability and the fact that quantum computers are mostly non programmable (there's not even one qubit logic gate..) TLDR quantum computing is going nowhere (excluding the low probability of a breakthrough in the field)

q_eng_anon 7y ago
'non-programmable'... um what?

WhitneyLand 7y ago

Here's why IBM says quantum supremacy is not relevant https://www.quantamagazine.org/quantum-supremacy-is-coming-heres-what-you-should-know-20190718 https://www.quantamagazine.org/quantum-supremacy-is-coming-h... From the article Quantum supremacy, we don’t use [the term] at all, said Robert Sutor, the executive in charge of IBM’s quantum computing strategy. We don’t care about it at all. The article also mentions practical considerations such as "quantum advantage", fault tolerance, and other initiatives competing with IbM. Relevant https://wikipedia.org/wiki/Quantum_supremacy https://wikipedia.org/wiki/Quantum_supremacy https://medium.com/@jackkrupansky/what-is-quantum-advantage-and-what-is-quantum-supremacy-3e63d7c18f5b https://medium.com/@jackkrupansky/what-is-quantum-advantage-...

The_rationalist 7y ago
The only real usefulness of quantum computers would be the supposed quantum supremacy. IBM not caring about Q supremacy is pure nonsense.
- _red 7y ago
  >would be the supposed quantum supremacy True. Another way he could have responded is: We don't care if quantum computers actually do anything useful, only that we can use the PR to get positive stock price movement.
  - jeffdavis 7y ago
    They could also say "We are scientists doing cool stuff, discovering things, and having fun. Maybe it will be useful someday but we aren't really focusing on that." Why are you attributing some kind of cynical motive?
    - pessimizer 7y ago
      Because it is a job, not a hobby, and is essentially about money. It's not cynical to ascribe venal motivations to employment, and to imply it is is a cheap shot.

WilliamEdward 7y ago

Quantum supremacy is usually misunderstood, and it's likely quantum computers will not surpass transistor computers in every way; they will be much better at a subset of tasks only.

quotemstr 7y ago
Right. And the "quantum computer" won't ever really exist anyway: we'll just end up with quantum functional units on regular computers. We attach GPUs and TPUs to regular CPUs, but we don't call the resulting machines "graphics computers" or "tensor computers".
- ineedasername 7y ago
  Actually, the term "graphics workstation" isn't uncommon, and "gaming rig" is a very common term for machines with great big GPUs attached.