[Cryptography] Why full-fledged quantum computers might always be five years away

[Jon Callas]

> On Aug 3, 2026, at 19:25, Peter Gutmann <pgut001 at cs.auckland.ac.nz> wrote:
> 
> Jon Callas <jon at callas.org> writes:
> 
>> What is a quantum computer? The question feels deceptively simple. It is a
>> computer that uses quantum effects to run calculations
> 
> Which is what current physics experiments (misleadingly labelled as computers)
> are not:
> 
>  computer, n: a programmable electronic device designed to accept data,
>  perform prescribed mathematical and logical operations at high speed, and
>  display the results of these operations
> 
>  experiment, n: A scientific procedure undertaken to make a discovery, test a
>  hypothesis, or demonstrate a known fact
> 
> With a "quantum computer" you take a known fact, the product of two primes,
> set up a physics experiment to demonstrate it and, if the experiment succeeds,
> issue a press release about your new factorisation record.
> 
> These are not "computers" no matter how much you bend the definition.  They're
> physics experiments, an exact match for the dictionary definition of an
> experiment, "a scientific procedure undertaken to demonstrate a known fact".

Note that I sent an article written by a journalist, and I both respect New Scientist and often roll my eyes at them. It's a legit opinion by a knowledgeable person, and relevant to our discussions.

Remember the D-Wave quantum computers? They're not the same architecture as others, can't run Shor or something else, but they might actually still be useful.

And analog computers were a thing ages ago, there's no reason they can't be again. Flight computers and other things were also just physics experiments, rather than computation.

And of course, as you note many times, they typically cheat. Is there even a single case of someone running the *proper* physics experiment as described by Shor? I don't think so, and await some actual real thing, too.

	Jon