The threat estimate for a quantum computer that breaks cryptography shall be based on currently available data and the understanding that only the Schor algorithm is known to provide exponential speedup for factorisation.
Let’s give IBM credit for attempting to factor in the number 35 in 2022, although they failed there [1]. Before that, the successful factorisation happened for the number 21 in 2012 [2] and the first factorisation of 15 in 2001 [3].
Now we have three points. There is a trend that the factorised number grows by a number of 10 for every ten years. Thus, to get a quantum computer that facilitates RSA-2048, we shall wait for 2^2048 years.
Let’s give IBM credit for attempting to factor in the number 35 in 2022, although they failed there [1]. Before that, the successful factorisation happened for the number 21 in 2012 [2] and the first factorisation of 15 in 2001 [3].
Now we have three points. There is a trend that the factorised number grows by a number of 10 for every ten years. Thus, to get a quantum computer that facilitates RSA-2048, we shall wait for 2^2048 years.
[1]: https://arxiv.org/pdf/2103.13855v1.pdf
[2]: https://www.nature.com/articles/nphoton.2012.259
[3]: https://www.nature.com/articles/414883a