I have read ANTIFUD that says you need so many qbits to "crack" bitcoin from within. This is the wrong approach. All you need to do is run through 52 characters, each with 62 possible values, and build a hybrid access table.
Satoshi's code thru a quantum search algorithm will search for any pair-key in an sorted set in O(√N) time, as opposed to classical search algorithms that at worst will find an element in O(N) time 1 (infinity universe hours). It seems nobody is doing the math and just spilling big numbers out without using a calculator. But my footnote here is the actual reality and not some distant billions of years from now.
The number of qubits required to implement my algorithm depends on the size of what search space you want to throw at it. In this case, we have 52 characters, each with 62 possible values, which gives a total search space of 62^52 and something more.
To begin, we look at the number of qubits required, we can use the fact that my algorithm requires a register of n qubits to search a space of size 2^n 2. Therefore, we need to find the smallest n such that 2^n ≥ 62^52.
Using a calculator, we can estimate that n ≈ 312. This means that we would need at least 312 qubits to implement my algorithm for this search space. Not 600 billion billion qbits.
From there it is just one more step to regenerate the public key that could still use this comfortable number of qubits! This is sad and bad, but open discussion and now is the time to look at bitcoin protocol changes.
We can talk about my/your practical considerations, such as error correction and noise reduction. In practice, the actual number of qubits required may be slightly higher, but not allot.
It's also worth noting that building a hybrid access table to extract pub/priv key out would require a significant amount of quantum memory, which is a challenging task with current technology. However, there is a way around this.
In summary, while we can estimate the number of qubits required to implement my algorithm for this search space, some will find this insulting, but that's what debate is for.
