The Venn diagram of "useful" and "not possible on a classical computer" has demonstrations on both disjoint ends but is currently empty in the intersection. For now. I fully sympathize with the hype-fatigue though.
That's on the useful end but I don't think any QC has gone beyond being able to factor 14 or something in that neighborhood. Realistically we'd need a few thousand qubits to factor anything that's reasonable and current QCs have a dozen or so qubits that work.
The "factorization" done with quantum computers involved cherry picking special numbers so that a special "compiled" circuit (knowledge of the answer is required in order to do this) can be used instead of the full thing. That makes the semantics of the executed program "slightly" different.
This effort is likely aimed at industrial/academic entities and not "you" as in a single person. But anyway, it needs to be emphasized that the phrase "quantum computer" is today used to mean anything ranging from
-a useless machine that produces a signal indistinguishable from noise
TO
-a highly sophisticated marvel of science and engineering that performs otherwise impossible calculations
Many industrial quantum computers today fall closer to the the former category than the latter. A single person or small team with minimal funding has basically no hope of building anything meaningful.
I don't know of any other device that has such a broad range of quality represented under one name. Maybe like calling ELIZA and Opus 4.6 both "AI".
This, for sure - if there were any risk of quantum computers with 64 or 128 functional qubits, expansion would be a matter of engineering - the development of real, actual, functional quantum computing is on the order of nuclear weapons development. The US government would make it secret, take it over, and scale it up to 1024 bits for immediate and near total cyber dominance; something like pre-emptive strikes on bank accounts, total pwning of adversaries' secure systems, planting command and control malware everywhere, grabbing intelligence from anywhere the administration saw as valuable. There are a ton of dead drop encryptions. They could move btc from Satoshis wallets and wreck crypto value.
Quantum computing research you hear about is "neat lab experiment" fluff, or a demonstration of corporate technical acumen and research capabilities. You won't hear about real quantum computing until well after it's been used in geopolitical conflicts.
Is there a QC out there that can perform a commercially useful computation? No, not yet. And yes snake oil is abound. But the reality is not two categories, it's a spectrum. Some are more useless than others.
No, it's not a spectrum in any meaningful sense. There are scam companies (some with semi-respectable research departments attached to them) and there are research projects. Anyone selling devices with the promise that those devices will do anything useful for their customers are simply lying.
It's like fusion energy: there are legitimate companies working on the problem, and they may even succeed at some point, but anyone willing to deliver a 1MW fusion plant tomorrow is scamming you, because the technology doesn't work yet.
The first QC that decrypts previously undecipherable text will have incalculable value to the government that surrounds it. QC companies are bullshit because they will take whatever free non-gov money they can, why not? They exist to absorb government money, rightly so, but their public profile is simply to get money from private sector sources
