that's the thing. so, the big quantum bogeyman is that elliptic curve public key derivation functions can be reversed with these hypothetical machines. if only they have a million qubits or something.

brute forcing a secret key is literally just making random keys and deriving the public key out of them. it requires an average of 2^128 iterations - 3.402823669×10³⁸ a number 38 decimal places long. if it takes a microsecond (1/1000000th of a second) to derive a key, which i think is somewhere in the range of real, my key generator does about 450,000 keys per second using bitcoin core's secp256k1 library) then:

1.078289752×10²⁵

1,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 years