We estimate that these circuits can be executed on a superconducting qubit CRQC with fewer than 500,000 physical qubits in a few minutes, given standard assumptions about hardware capabilities that are consistent with some of Google’s flagship quantum processors.
Google's current flagship Willow processor has something like 105 qubits.
I'm not knowledgeable enough to tell your brother when quantum computers will pose a real threat to bitcoin keys, but I don't think it's something that needs to cause him sleepless nights.
Additionally, Bitcoiners have a number of good options for mitigating quantum risks. Casey Rodarmor actually proposed a pretty cool solution (#1445101). But there's lots of others, including BIP 360. Some of these are getting close to being ready to implement (if people want to do it).
The Google paper says:
Google's current flagship Willow processor has something like 105 qubits.
I'm not knowledgeable enough to tell your brother when quantum computers will pose a real threat to bitcoin keys, but I don't think it's something that needs to cause him sleepless nights.
Put more bluntly:
source
Additionally, Bitcoiners have a number of good options for mitigating quantum risks. Casey Rodarmor actually proposed a pretty cool solution (#1445101). But there's lots of others, including BIP 360. Some of these are getting close to being ready to implement (if people want to do it).